A century-old food movement in the United States is making a come-back during the COVID-19 pandemic. This movement, known by some formerly as Liberty Gardens, can be traced all the way back to World War I. Today they are called Victory Gardens, and interest for them is growing fast.
Victory Gardens are home/public gardens introduced typically during times of national turmoil. There are multiple reasons people plant Victory Gardens during difficult times, but among the end results of these gardens are educating people, young and old, about a connection to agriculture, and bringing them together.
Dr. Rose Hayden-Smith, Emeritus, UC ANR, is an expert on Victory Gardens and authored Sowing the Seeds of Victory: American Gardening Programs of WWI about the history of home gardens in war-time America. Hayden-Smith is enthusiastic about the history and idea of Victory Gardens, and believes they can “lead us places.”
“What most people don’t realize about victory gardens is we all think about them about being the iconic home front mobilization program of World War II; they actually came first in World War I,” Hayden-Smith said. “There was one program part of this larger movement called the US War Garden Army. There was a large group of people in this movement that were concerned that their kids weren’t aware of the connection between agriculture and the public.”
Gardening was introduced as part of a rich curriculum to educate children and was viewed as an essential effort for national security,” Hayden-Smith continued. “There were concerns about morale during this time, and people thought gardening would give the country a national purpose.”
Public and government agencies came together for this movement in a way that is not seen as much today. With the success of these programs, people placed great meaning in the gardens, according to Hayden-Smith, pushing public message support in immense ways such as creating “poster art”.
“I think Instagram is the sort of poster art today that was prevalent during World War I and World War II, and has been a huge drive for interest in Victory Gardens today,” Hayden-Smith said. “I don’t think we’re going to see a decline in interest.”
Similar to today, there was a widespread pandemic during World War I when Victory Gardens made their first documented appearance. During this time, certain access to food was limited due to mandates from the pandemic as well as the effect it had on businesses. This caused concerns about food security, disruptions in food supply, civil unrest and concerns about being disconnected from the source of food.
The most beneficial aspect of Victory Gardens is their ability to give people a sense of food security and promote the important idea of food sovereignty. Since Victory Gardens enable virtually anyone to grow their own food in a sustainable fashion and have easier access to food during difficult times, many are starting to take to the idea of these gardens being a permanent staple after the pandemic.
“I think it’s going to take off like a rocket,” Hayden-Smith said. “While this pandemic is the worst, it’s helping people prioritize what’s important going forward. I think that people get it about the food now and why there’s been a crisis for a while. If you’d told me a year ago that food sovereignty issues would have been leading national news right now, I wouldn’t believe you, and I think that says something.”
Another beneficial aspect of Victory Gardens is the feeling of community they can create. During difficult times, bringing people together is important, especially when it comes to food choices and sources. Many that participate in Victory Garden movements do it for food security, but others do it for the sense of community and to help spread education about sustainable farming and agriculture.
“Our relationship between people and the landforms an alliance, and I think people don’t think about that enough,” Hayden-Smith said. “Community is one of the most important aspects of Victory Gardens. I think the conversion of prime public space to service the nation with these gardens is amazing. Prioritizing this is important, and people learn from each other.”
Now v. Then
Physically, the makeup of Victory Gardens is a bit different than how they were last century. Today, they consist more of container gardening with root vegetables and seasonal planting, according to Hayden-Smith. In terms of their purpose, though, they are more or less the same.
Having a close or direct connection to food sources and information is a driving factor for establishing Victory Gardens. Other reasons for gardening during today’s pandemic, Hayden Smith said, include wanting variety in diets (fresher and healthier ingredients), being closer to the land and becoming informed about sustainable agriculture. As was mentioned above, this reasoning is similar to the reasoning during the World Wars if not the same.
Victory Gardens are ultimately an under-researched topic in the world of organic farming and sustainable agriculture, but they have still proved to be widely beneficial over the last century. People like Hayden-Smith have been working diligently to prove this, helping people learn about the land and agriculture and integrate food sovereignty practices into their lives.
In recent decades, as California’s organic agriculture industry has grown, education and research on specific practices for organic agriculture has in some cases lagged behind that growth in acreage. The University of California (UC) now has a specific institute dedicated to organic farming in the newly created UC Organic Agriculture Institute (OAI). The OAI is housed within the UC Division of Agriculture and Natural Resources (UC ANR) and was established with endowments from Clif Bar and UC President Janet Napolitano. These endowments will provide the initial annual funds to support the efforts of the OAI, which will be focused on the development of research and extension programs for organic production of tree nuts, tree fruit, raisins and rice.
These efforts will be led by newly appointed Director Houston Wilson, a UC Riverside agricultural entomologist and Cooperative Extension Specialist based at the UC Kearney Agricultural Research and Extension Center in Parlier.
Resource for Organic Agriculture
One of the first steps for Wilson and the OAI will be to conduct a statewide needs assessment to determine the most critical research areas to focus their efforts on.
“Through a series of surveys, focus groups, cost studies and analysis of existing data on organic crop production, we will characterize the current status and needs of organic agriculture in California,” Wilson said.
This assessment, Wilson said, will also help the OAI identify relevant expertise within the UC system to develop multi-disciplinary research teams to address specific problems in organic agriculture. The OAI will also organize and facilitate regional crop-specific extension meetings, as well as an annual organic agriculture conference, to bring together growers, researchers, extension personnel and other industry stakeholders focused on tree nuts, tree fruit, raisins and rice.
“Some other potential activities include a small-grants program to help launch new projects and research fellowships for undergraduate students to gain experience in organic agriculture science,” Wilson said.
Wilson is looking to quickly establish the OAI as a center point of the organic agriculture industry, and networking for the purpose of collaboration and activity development.
“We are currently reaching out to build relationships with the many organizations and stakeholders in the organic agriculture community across California, as well as with growers, commodity boards and relevant programs within the UC and CSU system,” Wilson said. “As we design the OAI, we are building in multiple ways for these stakeholders to interact with and provide input on our programmatic activities (such as establishing an Advisory Committee.)”
Experience in Organics
While Wilson was only recently appointed as the OAI’s new Director, he is no stranger to organic farming practices. As Principal Investigator (PI) of the Wilson Lab at the Kearney Ag. Center, much of Wilson’s vineyard and orchard research has applications in organic agriculture.
“Many of the pest management practices we focus on do fall under the National Organic Program, such as crop sanitation, biological control, mating disruption, cover crops, improved trapping methods and sterile insect technique—but many of these practices are equally important for conventional and organic growers alike,” Wilson said.
While the goals of Wilson’s research and extension program are often relevant to the OAI, he considers these focused entomology activities separate from his role within the OAI, which will encompass many additional disciplines and target crops. As Director of the OAI, Wilson said, his primary role is not as a researcher, but rather to facilitate the development of a multi-disciplinary research and extension program for organic agriculture.
“Research and extension needs across our focal crops will likely encompass multiple disciplines, including pathology, weed management, crop nutrition, soils, irrigation and entomology,” Wilson said. “In this way, as Director, my job is to bring together the most relevant experts to address issues in these different areas.”
Even though Wilson has come into contact with many organic growers over the course of his career, he has never done so in such a targeted manner as he is now as Director of the OAI, he said. Nonetheless, he is still looking forward to entering an organic setting.
“I’m looking forward to meeting and working with new growers, organizations and other stakeholders,” Wilson said. “I previously never had a mandate to focus on organic, but now have the opportunity to fully delve into this sector of agriculture.
“California has always been a leader in organic agriculture, and as such there is a rich history here that involves a lot of great people who have worked for decades to develop, define and promote organic agriculture,” Wilson continued. “In this way, it is an honor to have been selected for the inaugural Directorship of the OAI and to now have the opportunity to interact with and learn from all of these different folks.”
Organic Agriculture Will Prosper
While California is already a prospering organic powerhouse, with 3,000 certified organic farms growing crops on 21% of all U.S. certified organic land, there is much more room for growth. Certified organic products are in demand and the UC OAI will provide guidance not only to currently certified organic growers, but also to farmers looking to make the switch from conventional to organic agriculture.
“We will likely organize annual and/or regional extension meetings for our focal crops,” Wilson said. “These will provide a training opportunity for growers that are currently certified, as well as those that are interested in transitioning to organic.
“We may even schedule events that specifically target growers that are looking to transition,” Wilson continued. “There is some grant funding available for projects that target transitioning growers, so that might be a good place to find financial support for these efforts.”
Among both organic and traditional producers, an increasing number of farmers are seeking greener alternatives for weed and pest management. Heat treatment technologies like propane-powered flame weeding systems and Thermaculture provide a unique alternative and solution, offering many benefits over conventional herbicides and mechanical weed removal advantages.
Propane flame weeding offers a highly efficient and organic alternative to herbicides or tedious manual labor. According to field studies funded by the Propane Education and Research Council, flame weeding is up to 90% effective against weeds by using intense heat to rupture plant cells, causing the weeds to wither and die. Approved for certified organic farming operations, propane flame weeding also avoids the disruption of essential soil nutrients, which commonly occurs with cultivation and tillage weed control methods.
The flame weeding system is available as a handheld torch or as torches and burners connected to a tool bar with the propane tank mounted onto the back of a tractor. Either way, the process is quick and easy, leading to improved efficiency for farmers.
Additionally, flame weed control is a flexible solution that can be used in a variety of weather conditions. Flame weeding can be used to weed fields early before seedlings have started to come up or late (after harvest) to prepare for the next spring. Farmers know that timeliness is critical for a successful operation and, fortunately, propane systems can help them stay on track, even when field conditions aren’t ideal or during seasons of wet or erratic weather.
In 2010, Certified Organic Farmer Larry Stanislav participated in a research study with farming partner Elizabeth Sarno, who was an extension educator and organic research project coordinator for the University of Nebraska. The Propane Council worked with university researchers to fund a study aimed at increasing the efficiency of propane flame weeding systems in organic cropping systems.
Results from this study showed that a hooded propane system increased heat concentration on weeds while reducing fuel use, which improved the effectiveness and efficiency of propane flame weeding. Study participants reported weed control levels as high as 95%. The research led to the development of a training manual for the practice in corn and soybeans and the commercialization of a four-row banded/full propane flame weed control system marketed under the name Agricultural Flaming Innovations. Since this study, there have been several advancements to the technology, making propane flame weeding systems even more efficient and beneficial than ever before.
For Certified Organic Farmers like Stanislav, flame weeding systems have become an essential tool for weed control. He estimates that for his 50-acre plot of organic corn, it saves him at least 30 hours of labor time compared to traditional weed control techniques.
“Using a propane flame unit to control weeds also eliminates disturbance of the soil,” said Stanislav. “You might spend more on the equipment at the outset, but in the long run, soil health and increased yield are big benefits.”
While propane flame weeding has been around for years, new innovative models make the use of heat treatments for weed removal more effective than ever. Research supported by the Propane Education & Research Council has shown that weed flaming provides approximately 95% effectiveness in weed control for a variety of crops. Propane is a clean, non-toxic, non-poisonous fuel that won’t contaminate nearby crops, soil or groundwater. Plus, it’s an approved clean fuel under the Clean Air Act of 1990 and produces fewer greenhouse gas emissions than other fuels such as diesel and gasoline.
A new technology that initially delivered dividends in the highly scrutinized world of wine making is now available for a whole new segment of growers that want a sustainable, chemical-free alternative to controlling insect and fungal infestations and weeds. This emerging practice is called Thermaculture, a propane powered heat application pioneered by Agrothermal Systems.
“We thought to ourselves, ‘what if we could give growers heat on demand, which is basically the sun on demand’,” said Drew Sanders, CEO of Agrothermal Systems. “We’ve been finding niche areas where too much heat, too little heat or too much moisture is a problem, and coming in to help growers.”
Thermaculture heat protocols work with Mother Nature to raise the natural defense system of plants, interrupting most insect and fungal development. It also helps fight disease and crop damage by drying out crops after it rains. When applied in vineyards, it’s proven to increase fruit set and yield. The heat raises the plant temperature to the levels needed for optimal fruit set and growth, even in cold, wet weather. Users on average see a 24% increase in fruit set and 20% improvement in yields, according to Agrothermal.
In studies conducted in 2017, Agrothermal Systems saw fungicide use reduced by at least 50% during several wine grape trials. Since then, this heat technology has expanded to show its benefits for general produce and specialty row crops, too. When used for produce and specialty row crops, this method helps to fight disease and crop damage by drying out crops after rainfall.
According to a study by Caltec Ag of Modesto, Calif., Thermaculture heat treatments provided several benefits including cost. The propane used per acre to produce the heat was about six gallons per acre, for a price of roughly $10.
Michael Newland is director of agriculture business development for the Propane Education & Research Council. He can be reached at email@example.com.
Trace elements, including zinc and several other micronutrients, have become a topic receiving much greater emphasis over the last few decades. These nutrients, though needed in much smaller amounts than the primary elements like nitrogen, phosphorous and potassium, are nevertheless essential for crop growth, soil and plant health, and for the production of nutrient-dense food and feedstuff.
One comparison that farmers and growers can appreciate is that trace elements in the soil function somewhat like spark plugs in a motor. Though only needed in small amounts, they are essential as catalysts or activators for many plant processes. They are necessary for top performance from any soil or plants being grown there.
The list of micronutrients considered as essential may vary depending on the crop and/or soil being considered. Those most generally included on soil tests are boron, iron, manganese, copper and zinc. Molybdenum (especially for legumes) and cobalt (especially for livestock and soil microorganisms) should also be considered where they could be deficient enough to cause problems, but the costs are such that for many growers, only key areas are initially tested and treated accordingly. Chlorides can also be tested for growers who may have a problem with salty water or salt deposits on their land. Some also test for silicon and selenium, but the levels and needs are not as well understood and defined for these elements as for those aforementioned above.
Zinc in Soil
Zinc is likely the most accepted and most often applied of all the trace elements. It is perhaps the least controversial micronutrient of all those mentioned above. Zinc is widely applied and considered as most necessary on crops like corn, rice and pecans. For example, adequate zinc is needed to determine the size of the ear (i.e. the number of kernels) of corn during the early growth stages (V4 and V5). But all crops respond well to zinc when it is correctly supplied.
The weight of the total amount of elemental zinc per acre found in the aerobic zone of the soil (which is the depth to which a wooden fence post rots, generally 6.5 to 7 inches deep) can be from 20 pounds to 600 pounds per acre. But most of that zinc is not in a form the plants growing can take up and utilize. Most of the zinc in the soil is “tied up” or “locked up” and unavailable to be taken up and used by the growing crop.
What needs to be determined is how much zinc is present in each soil in a form that is available for plant uptake and use. The total amount of zinc in all forms, whether available for plant use or not, can be determined by a soil test. But the determination most needed is the amount of zinc in the proper form for plants to take up and use which is considered as the amount of plant-available zinc in each soil. Of the total zinc contained in each soil, a minimum of 12 pounds per acre is needed to avoid zinc deficiency in a growing crop.
There are those who grow organically that may dismiss any need for adding zinc or other trace elements to the soil as they expect such materials will be provided by the use of compost or other natural methods. Zinc from compost and manures is useful, but that amount is seldom if ever enough to increase measurable levels in a zinc-deficient soil. Perhaps this is due to the bio-availability of zinc from composted materials which allows more immediate uptake by plants.
Using bone meal can increase measurable zinc levels in the soil over time. Growers who have applied large amounts of bone meal may have sufficient, or even excessive, levels of zinc in the soil. In fact, it can build the zinc levels too high when used in excess which then affects phosphate availability and, if high enough, it can hurt availability of other nutrients such as magnesium, manganese and copper as well.
But what happens when such is not the case and zinc levels are actually deficient in the soil? What difference does it make? And even if it does matter, how can growers know when the soil has too little, too much or just the right amount?
Deficiencies and Availability
Using soil tests is one method that can help evaluate whether zinc levels in the soil are adequate, but far too many who grow organically are just not sure whether to place their trust in such methods or not.
There is an old saying with which many organic growers can identify – “Study nature, not books!” So, perhaps looking at what happens in the field can provide some initial directions that can then be correlated back to what a detailed soil analysis can or perhaps cannot actually show in such cases. A better understanding about zinc and how to use it can help growers determine when whatever methods being used should be considered as sufficient or insufficient for supplying the needs of crops grown on that soil.
Zinc is one of the easiest trace elements to build. Even in soils that are extremely deficient it can be sufficiently applied to adequately reach required minimum levels for the very next crop. It is generally the most economical to correct and maintain of all those trace elements.
It is well-known that zinc is commonly lacking in plants grown in soils that have excessive phosphate levels. This is one of the first big hurdles that organic growers who use large amounts of compost must eventually face. Use of too much compost will at some time in the future ultimately result in too much available phosphate in the soil. Once that happens, zinc availability suffers. This can still be the case in soils with adequate to high or even excessive levels of zinc.
Too much phosphate in the soil can affect zinc availability to the point of reducing water uptake needed by the plants growing there. Zinc is essential for moisture absorption by plants. When soils have enough zinc for correct moisture absorption, they generally have enough zinc for performing the other needed functions in the crop as well.
Deficiencies tend to be greater in lower exchange capacity soils such as sands or very coarse clays. Deficiency symptoms are expected most in new growth. Smaller leaves or leaves that wilt very soon after watering for example indicate a possible serious need for zinc. An accurate soil test can be used to determine when zinc is needed and in what amounts.
Soil Needs and Testing
What level of zinc is needed in the soil? Always keep in mind that there are several different ways to test for, measure and report zinc levels for the soil, and most tests will read far lower than the figures from the testing that actually reflects the need for zinc on a pound for pound basis. So, do not try to universally apply the test numbers from one laboratory to other soil tests to determine if zinc is deficient or not. If so, you could wind up applying far more zinc than is needed to the soil.
On the other hand, there are soil tests that some soil laboratories use that consider zinc as adequate when tests that measure zinc needs on a pound for pound basis show as still too deficient. How do growers know which one is right? How can that be best determined? First judge by how crops respond and then by measuring what levels are needed in the soil to provide the proper response.
For best results, match phosphate and zinc needs for each different soil. On soils with very low phosphate levels, plant-available zinc measured as needed on a pound for pound basis should be at the minimum requirement of 12 pounds per acre or 6 ppm. When phosphate reaches excellent, zinc should be 20 pounds per acre or 10 ppm, and if excessive, then 40 pounds per acre or 20 ppm. Just remember, when phosphate is excessive enough so as to affect zinc availability, it will require more water to produce the same potential crop yield.
On the other hand, extremely excessive zinc can reduce phosphate availability and can cause other problems that may not always be as obvious as the actual example being shown here.
Figure 1 shows an example. The weed growing there is generally not that common in fields in the area. It is field pennycress that appears to have been planted right in the row where the corn was planted last year. The same weed is growing in the middles, but notice in the photo titled Figure 2 picture that it is not nearly as mature and vigorous as those growing in the old cornrows.
Samples of both the soil and the plants were taken in the rows and the middles. The plants growing in the row had extremely high concentrations of zinc. The same extreme zinc levels were also shown to be true for that soil. In fact, the rows had extremely excessive zinc levels right where the weeds were growing best, but out in the middles, the soil test showed zinc levels were quite deficient. The type of zinc used had built it up to excessive levels right under the row where it was applied but had no influence on levels even inches away.
This helps to illustrate what can happen when too much of any nutrient is applied to a soil directly under the seed. How much does it require before the availability of other nutrients (namely phosphate in regard to excessive zinc) starts to be reduced? Plants send their roots directly to the richest source of nutrients as fast as they can do so. This has been shown to be true not only for banded fertilizers but even for small clumps of manure or compost as well. These sources will quickly attract plant roots. Could this be why some farmers who band their zinc believe they need to add more phosphate when the soil test levels show to be far more than adequate for growing the crop?
Building up the availability of zinc in a soil can be accomplished with one broadcast application. The proper forms of zinc (some forms are soil feeders while others are only plant feeders) are quickly available and easy to build in a soil when those needs are correctly measured and the correct form is applied. Even in severe cases of deficiency, provided there is sufficient calcium there to get the zinc into the plant (a minimum of 60% base saturation on the test we use), zinc that has been taken up in sufficient amounts for the crop, even grass and trees, can make a difference in the plants growing there in three days.
One client who was growing turf grass reported that the grass just could not get enough water. Even though the soil was still wet from the previous irrigation, the grass would begin to wilt and only applying additional irrigation water would solve the problem. They had a severe zinc deficiency.
Based on the need shown by doing a soil test, the required amount of the correct form of zinc was applied as a broadcast application to sufficiently build up the level in the soil. The problem was solved in just three days! After that, normal irrigation was sufficient to grow excellent grass. The soil had everything else it needed, but the lack of supplying enough zinc was the problem.
The effectiveness of the various forms of zinc can be determined when the testing being done reflects the amount that is applied to the soil on a pound for pound basis. When this is the case, growers can soon see which products are most effective for use on the crops they are growing.
But too many forget that it takes two years to measure the full effects of a zinc application on any soil. The efficiency of zinc also depends on an adequate supply of calcium which is not accurately determined by the pH of the soil. Many soils have a “good” pH but lack calcium in sufficient amounts to take up zinc and other trace elements properly. The true determination of calcium needed is whether the soil in question has a base saturation of 60% calcium or higher. The lower the calcium saturation drops below 60%, the harder it is for plants to adequately respond, even when zinc levels are sufficient.
There are several different sources of zinc available for use by organic farmers. Those materials should first be divided into one of two classifications. Is the zinc being applied as a soil feeder or a plant feeder? If the form of zinc is a plant feeder, applying what should normally be considered as sufficient amounts to build up soil levels will not be successful. On the other hand, those forms of zinc that work as soil feeders should show zinc levels are being built on a pound for pound basis at the end of two years.
Rice is an excellent crop to use as a test to show the accuracy of a soil test and whether the zinc being used is a good soil feeder or only a plant feeder. When there is less than 12 pounds (6 ppm) per acre of zinc in a soil used for growing rice, the tips of the rice blades will begin to die. The problem is called “bronzing of the tip”, and on zinc-deficient fields it generally shows up by the time the first top-dress of nitrogen is needed by the rice crop.
If the soil test shows the soil has 6 pounds (3 ppm) of actual zinc, then it needs another 6 pounds to reach the minimum required 12 pounds per acre. This means the soil needs the equivalent of almost 17 pounds per acre of a standard 36% zinc sulfate to correct the problem via the soil.
There are other forms of zinc that cost less that can be applied and still eliminate this same problem in a rice crop. Farmers can apply the same amount of zinc using 36% zinc oxysulfate which costs less and solves the problem. An equivalent amount of foliar zinc chelate or even a plant extracted foliar zinc will do the same.
But all of these products that substitute for zinc sulfate are designed to be used as plant feeders. They supply just enough zinc to solve the problem, but the next time you grow rice there or if you grow rice there again the next year, you have to use the same amount again to solve the same old problem – year, after year, after year.
But a true zinc sulfate is a soil feeder. Supplying a sufficient amount of zinc to reach 12 pounds per acre just once when using it will solve the problem with only that one application for five to seven years before needing another maintenance application – generally about another 10 pounds per acre of 36% zinc sulfate. All soils need to at least maintain the 12 pounds of zinc per acre which is the actual minimum amount needed for all crops. Provided the soil has the minimum amount of needed phosphate and adequate calcium, the proper form of zinc will work there very well.
Just how important is it to maintain this minimum 12 pounds per acre level of zinc? Perhaps the response of soybeans to adequate zinc will prove to be a good example. When sufficient amounts of all the other nutrients are provided and zinc levels show to be 10 pounds (5 ppm) per acre rather than the required 12 (6 ppm), then supplying 10 pounds per acre of a true 36% zinc sulfate will increase the soybean yield by 10 bushels per acre. And if you use a true zinc sulfate (a soil feeder, not a plant feeder), that benefit will last about 5 to 7 years or even longer if you are using sufficient amounts of compost.
Once out of the aerobic zone, available zinc tends to decrease more and more as you probe deeper into that soil. Zinc, like phosphate, will always be most available in the aerobic zone. This is true unless the top soil in the field has been eroded away by wind or water, or when it has been removed and not put back where land has been graded or scraped for leveling. Another example is when the top soil is removed with the crop such as in harvesting turf grass.
All materials should be applied as a broadcast application that tend to help build up nutrient levels in the soil. For example, 36% zinc sulfate will increase zinc levels pound for pound when applied on the soil. Once applied it will remain there in the soil in an available form until utilized by the crop or the biological activity that supports crop growth. Such products are considered as soil feeders. They do not tie up easily once applied to the soil where proper treatment of the soil is practiced.
On the other hand, 36% zinc oxysulfate tends to be a plant feeder. When it is applied at the same rate as 36% zinc sulfate, much of the time the zinc level in the soil does not change at all. It is made by predominantly using a cheaper form of zinc, zinc oxide, in combination with a proportionately smaller amount of zinc sulfate. Some of these products do serve as soil feeders. It appears that when the zinc oxide is completely pulverized and then combined with zinc sulfate, it will help build zinc levels in the soil. If the product will build available zinc levels as measured by a reliable soil test on a pound for pound basis, then it is considered as a true soil feeder for building and maintaining needed zinc levels for soil and crop needs.
Effects of pH
There are far too many false concerns about the effects of high pH on zinc availability. It is true that as the pH of a soil goes up, the available zinc levels in that soil will be reduced accordingly. But the effects of the pH increase are only a concern for the zinc that is already there.
For example, on soils with a pH of 8.0, if the plant-available zinc is below the needed minimum of 12 pounds per acre, then applying an appropriate amount of 36% zinc sulfate will build the level of plant-available zinc right back to the prescribed amount. With a soil test that truly measures plant-available zinc and the use of a true zinc soil feeder fertilizer product such as 36% zinc sulfate, the levels will come right back to where they need to be in two years’ time. On high pH soils, it happens all the time.
If this does not work on a particular soil, there is generally a good common-sense reason as to why. First, was it truly a soil feeder form of zinc, or could it possibly have been a plant feeder form instead? Second, did the soil test used truly measure and express the zinc level on a pound for pound basis or is some other test being substituted to help make it “quicker and cheaper” to perform?
In addition, keep in mind that an excessive amount of phosphate can tie up available zinc in the soil. So can using extremely high rates of nitrogen or applying excessive amounts of manure or compost. The only way to know for sure is to find a test you can count on to measure what is actually there in the form needed to supply the crop.
On soils that receive limestone applications, the availability of micronutrients will be reduced. This is of greatest concern when the soil has borderline or deficient trace element levels. This includes zinc levels that do not remain above 12 pounds of plant-available zinc per acre once enough time has passed and the lime has had time to completely react with the other nutrients in that soil. This can require as much as three years to see the full effects on the nutrient levels in that soil, including plant-available zinc. If the field has borderline zinc levels and none is added, it may be the first, second or third crop before the zinc drops to a deficient level. The only way to know for sure is to monitor the plant-available zinc before each crop is grown.
This then should bring up one more consideration when it comes to assuring the soil in each field has enough zinc. Once you have a test that can measure and report what the zinc level should be, how often should you test that field to assure the zinc and everything that can affect it is still in order? Some will advise testing the soil every three or four years to “save money” – REALLY?
As one farmer stated after learning the value of using soil tests to maximize nutrient content and encourage better yields, “A soil test costs less than one small bale of hay per acre, and I can lose a lot more than that if just one nutrient is not properly supplied for growing the next crop.”
Start small, but prove it for yourself – you must, as most soil tests are used to sell you something, not teach you something.
For those who may be interested, boron is the next micronutrient to be discussed in this series of articles on trace elements and their usefulness for organic growth.
Neal Kinsey is the owner and President of Kinsey Agricultural Services. Please call 573 683-3880 or see www.kinseyag.com for more information.
One of the few things people can agree on about biostimulants is that they are difficult to define. The Biological Products Industry Alliance (BPIA) suggests:
“Plant biostimulants contain substance(s) and/or micro-organisms whose function when applied to plants or the rhizosphere is to stimulate natural processes to enhance/benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress and crop quality.”
What is a Biostimulant?
Biostimulants are hard to define as there are many different substances and microorganismal inoculants used in their production. It is also difficult to quantify the mechanisms for how biostimulants work and ultimately provide benefits to crop health and quality.
Commercial products may have several different ingredients such as amino acids, micronutrients and beneficial microbes. Biostimulant research has focused on many different products, tested on different crop species, in different environments. Some studies have shown evidence for biostimulants reducing the impact of stressors on plants, but this has not been universal.
A review paper by Povero et al. shows examples of reported biostimulant effects including enhanced fruit set, size, quality, root development, plant growth, water and nutrient uptake, stress mitigation and soil improvements. Another review discussed 26 different biostimulant studies conducted on fruit trees (Tanou et al. 2017). The categories of products (used individually or sometimes in combination) included protein hydrolysates, seaweed extracts, humic substances, leaf/pollen/yeast extracts, amino acid chelate and Leonardite extract. This broad range of products and effects can make it difficult to decide whether anyone biostimulant will be helpful for a particular situation.
Biostimulants are not currently regulated in the United States as they are classified differently from fertilizers and pesticides. However, it is possible that they will be regulated in the future. In spring 2019, the EPA released for public comment a “Draft Guidance for Plant Regulators, Including Plant Biostimulants”. There has not been a new update since then, but it is possible that some biostimulants, which have the properties of plant growth regulators, will become subject to the Federal Insecticide, Fungicide and Rodenticide Act, which will require registration and labeling. If this happens, it may change what products will be available, but will also provide some oversight to the industry.
How Biostimulants Function
Biostimulants have a different function than fertilizers. Fertilizers are used to add macro- and micro-nutrients to the crop, which improves crop growth. Like fertilizers, biostimulants can be applied either foliarly or through the irrigation system and may contain some low levels of nutrients. However, the addition of nutrients is not their main purpose. They are more likely to be used to add biological products such as microbial, acids, and hormones to the plant and soil to aid in specific functions such as stress tolerance or fruit quality.
To date, most of the studies that have been done on biostimulants have been on vegetable crops, possibly because they can be completed more quickly than permanent crops. Also, permanent crops contain reserves of nutrients in their woody structures, which could become a confounding factor in their evaluation (Soppelsa et al. 2018). Even when all applied substances have been controlled, permanent plant tissue can release nutrients to assist in plant growth in ways that are difficult to account for. This makes it more challenging to determine if an observed effect is due to the applied biostimulant or not.
As mentioned earlier, many biostimulant products contain multiple components, which can make identifying the causal agent difficult. For example, in a potted almond trial, Saa et al. applied two different products to two-year-old trees. One product was from seaweed extracts, and one was from the microbial fermentation of a proprietary mix of organic cereal grains. The seaweed extract product also contained amino acids, glycosides, betaines and vitamins. This study was especially interested in potassium, and it compared both biostimulant treatments to a foliar potassium treatment and a control. All four treatments were applied to trees that had been fertilized with either adequate or low levels of potassium, with all other nutrients controlled for. The results showed that both biostimulant treatments increased the shoot length and biomass when potassium levels were adequate, but only the seaweed-based treatment was also effective in the low potassium treatment. That would seem to indicate that potassium was a limiting factor and that the seaweed-based product was able to resolve that, but the microbial fermentation product contained even higher levels of potassium, so the actual mechanism is still unclear (Saa et al. 2015).
Another biostimulant trial done on young almond trees in Spain compared the combined application of two biostimulants to control treatment in three almond cultivars with two irrigation treatments (Gordillo et al. 2019). Each of the biostimulants had multiple components. One had a combination of aerobic and anaerobic bacteria. The other was extracted from shrimp meal through a microbial fermentation process and contained amino acids, nitrogen and trace levels of other nutrients. Each of the three cultivars had a slightly different response to the treatments. In biostimulant-treated ‘Guara’ trees, there was a higher leaf water potential (less stress) than in the control under both irrigation regimes. The treated trees also had higher yields in both irrigation regimes. Biostimulant-treated ‘Lauranne’ and ‘Marta’ trees had higher stomatal conductance than control during vegetative stages, and ‘Lauranne’ trees’ stomatal conductance was also higher during kernel fill. This study shows that even within a particular species, biostimulants may have different effects. However, this study only had one season of data collection, so it is unclear whether the results can be replicated.
Seaweeds are one category of biostimulants that have shown a lot of promise. In a review article on seaweed biostimulants, Battacharyya et al. referenced over 50 seaweed studies that have been conducted on vegetable and fruit crops as well as ornamental crops and turf grasses. The reported effects included increased germination, increased yield and increased uptake of various nutrients. In a different study of brown seaweed, Ascophyllum nodosum, researchers found that skin total anthocyanins at harvest were significantly higher in wine grapes treated with the biostimulant than in the untreated control (Frioni et al. 2018). The first year of the study was conducted in Italy with two different concentrations of the seaweed extract on Sangiovese grapes. The second year of the study was conducted in Michigan with one concentration of the biostimulant applied to two grape cultivars: Pinot Noir and Cabernet Franc. The goal was to test out the seaweed extract in different climates and in different cultivars. The anthocyanin level was the one factor that increased in all seaweed biostimulant treatments in all cultivars in both locations, indicating some consistency.
Although there is anecdotal support for the use of some biostimulants, more replicated research trials are needed to demonstrate which products are effective for which crops in which situations. If the mechanism for how the products work can be defined, it will make it easier to decide when and how they should be used. There are many different products on the market, and if growers are interested in trying them out, they should contact their local farm advisors, PCAs or CCAs to help them set up a demonstration trial. Products should be chosen based on the needs of the crop, and compared to an untreated control. For best results, conduct trials over multiple seasons.
Battacharyya, D., Babgohari, M.Z., Rathor, P. and Prithiviraj, B., 2015. Seaweed extracts as biostimulants in horticulture. Scientia Horticulturae, 196, 39-48.
Frioni, T., Sabbatini, P., Tombesi, S., Norrie, J., Poni, S., Gatti, M. and Palliotti, A., 2018. Effects of a biostimulant derived from the brown seaweed Ascophyllum nodosum on ripening dynamics and fruit quality of grapevines. Scientia Horticulturae, 232, 97-106.
Gutiérrez-Gordillo, S., García-Tejero, I.F., García-Escalera, A., Galindo, P., Arco, M.C., Durán Zuazo, V.H., 2019. Approach to Yield Response of Young Almond Trees to Deficit Irrigation and Biostimulant Applications. Horticulturae, 5, 38.
Povero, G., Mejia, J.F., Di Tommaso, D., Piaggesi, A. and Warrior, P., 2016. A systematic approach to discover and characterize natural plant biostimulants. Frontiers in plant science, 7, 435.
Saa, S., Olivos-Del Rio, A., Castro, S., Brown, P.H. 2015. Foliar application of microbial and plant based biostimulants increases growth and potassium uptake in almond (Prunus dulcis [Mill.] D. A. Webb). Frontiers in Plant Science. 6, 87.
Soppelsa, S., Kelderer, M., Casera, C., Bassi, M., Robatscher, P. and Andreotti, C., 2018. Use of biostimulants for organic apple production: effects on tree growth, yield, and fruit quality at harvest and during storage. Frontiers in plant science, 9, 1342.
Tanou, G., Ziogas, V. and Molassiotis, A., 2017. Foliar nutrition, biostimulants and prime-like dynamics in fruit tree physiology: new insights on an old topic. Frontiers in Plant Science, 8, 75.
Effective organic farming begins below ground in just a few inches of high-quality topsoil. Intuitively, we recognize healthy soil in the spongy give beneath our feet. We can scoop it up, see the dark color and smell the distinctive, rich aroma of organic matter and active microbiology. Bacteria, fungi, archaea, nematodes and nameless other organisms quietly feed and defend our crops against pests and pathogens.
Crop protection challenges every grower, but in organic production, controlling pests and pathogens proves especially difficult. Without synthetic pesticides, root and foliar diseases often take a greater toll, and insect pressure can become overwhelming. While organic crop protection materials provide indispensable support, integrating preventative measures may greatly improve crop quality and yield.
Countless microscopic soil organisms orchestrate dynamic defense strategies against a small fraction of pathogens. By feeding, coaxing and fostering the soil’s beneficial life, organic farmers can turn on ancient defense mechanisms to suppress soil borne diseases and herbaceous insects. Healthy rhizosphere ecosystems evolved over millennia to cope with biotic and abiotic stress. Organic growers can improve crop protection by stewarding healthy soil microbiology. In return, the microbes will diminish disease symptoms by increasing nutrient availability, improving soil quality and inducing plant systemic resistance against pests and pathogens.
Nutrition as Pest Defense
Crop nutrition directly impacts crop protection. Plants rely on essential macro and micronutrients throughout their life cycle not only to support growth, but also to defend against invading pests and pathogens. In conventional farming, growers can apply precise quantities of macro and micronutrients in plant available form. Organic growers must rely on soil microorganisms to break down complex organic matter into simple, plant available nutrients.
Nitrogen, phosphorus, potassium and micronutrient availability depends on how quickly and effectively the soil microbes can metabolize and release nutrients. Microbial activity depends on soil moisture, temperature, carbon to nitrogen ratio and many other factors. Growers can create a soil environment conducive to microbial nutrient cycling by feeding microbes plenty of carbon, keeping the carbon to nitrogen ratio around 20:1 and keeping the soil moist but not saturated. Organic growers feed the microbes and the microbes feed the crops. Supplying frequent, moderate doses of liquid organic fertilizer can also stabilize nutrient availability, preventing spikes and crashes caused by high rates of manure or pre-plant fertilizer.
Nitrogen is the most limiting nutrient to crop growth and, without an adequate supply, development slows, and plants often suffer increased damage from disease and pests. Providing enough N to meet demand at critical growth stages will help seedlings mature quickly and develop strong root systems resilient against disease. Too much nitrogen can be equally damaging. Excessive N increases vegetative growth, and pests and pathogens are drawn to the crop to feed on succulent, tender young tissue2. Frequent leaf and soil tests can help determine N availability and fertilizer requirement.
Phosphorus availability also affects disease suppression. P is critical to root development, so supplying adequate available P will help plants develop mature root systems as quickly as possible to evade infection during their vulnerable infancy2. P availability greatly depends on pH, so adjusting the soil pH to around 6.5 with sulfur, lime or lots of organic matter can help support healthy root development. Adding too much P can harm crop growth and disease suppression, limiting the growth of some beneficial fungi that can outcompete or inhibit pathogens. Beneficial fungi also aid nutrient and water uptake, indirectly proving disease management by facilitating vigorous growth. Excessive P also decreases zinc availability, potentially causing deficiency symptoms that increase pest and pathogen damage.
Potassium, calcium and micronutrients play critical roles in cell wall stability and plant defense. Deficiencies lead to cracks and damage in cell walls and membranes, giving pathogens entry points into the plant. Fertilizing with adequate K, Ca and micronutrients builds thick, protective cell walls rich in lignin and suberin that resist breakdown by enzymes released by attacking pathogens. Nutrient deficiencies also cause sugars and amino acids to build up in cells because the plant does not have the nutrients needed to transform simple building blocks into complex carbohydrates and proteins. Sugars and amino acids leak out of weak cell walls, attracting and feeding pests and pathogens.
Microbial activity and organic matter influence disease suppression by improving many aspects of soil quality including structure, pH, cation exchange capacity and water holding capacity. Good soil structure with stable aggregates and plenty of pore space favor healthy root growth and beneficial microbial colonization. Fusarium wilt often occurs in acidic, saturated soils when pathogenic fungi prey on oxygen-starved roots. Without adequate porosity, crops either get too much or too little moisture, making them weak, inhospitable to beneficial microorganisms and susceptible to pathogenic attack. Maintaining structured, well-aerated soils gives roots the best opportunity to grow and develop strong beneficial microbial associations. The good fungi and bacteria will occupy space on the roots and adjacent soil, competitively inhibiting pathogens and parasites.
Soil microorganisms are ecosystem engineers that modify their surroundings to suit their needs. Fungi and bacteria excrete sticky substances that bind soil particles together, creating aggregates and pore spaces that facilitate water, nutrient and air flow. By cover cropping and applying compost and carbon-rich organic fertilizers, growers provide a food source to fuel microbial growth and soil structure development. Over time, fungal and bacterial colonies will change the soil’s physical and chemical characteristics, creating an environment suppressive to pathogens.
Organic matter also contributes to disease management by increasing water holding capacity and cation exchange capacity. Organic matter has a very high water holding capacity compared to the mineral fraction of soil. Organic matter soaks up water like a sponge, slowly releasing moisture without suffocating plant roots. Organic matter also has very high cation exchange capacity, meaning it can attract and hold positively charged plant nutrients such as ammonium, potassium and calcium. Improved nutrient and water holding capacity provide plants with plenty of nutrients needed for vigorous growth and defense against stress.
Increasing soil microbial activity also helps fight biotic stress by activating the plants’ “induced resistance” against attacking organisms. Researchers describe two main types of induced resistance – Systemic Acquired Resistance (SAR) and Induced Systemic Resistance (ISR). Both forms activate plant defense genes and enhance protective mechanisms. SAR increases salicylic acid levels and is associated with accumulation of pathogenesis-related (PR) proteins.
Many different microorganisms and some abiotic chemical compounds can activate SAR. ISR relies on activation by plant-growth promoting rhizobacteria (PGPR) such as some types of Pseudomonas living symbiotically in the root system5. ISR also differs from SAR in defense mechanism. ISR is associated with the plant hormones jasmonic acid and ethylene and does not cause an accumulation of PR proteins. Both types of resistance prime the plant to recognize and strongly respond to a wide range of pathogens by launching chemical and physical defenses against infection.
Build Suppressive Soils
Pest or pathogen presence alone does not inevitably result in disease. The interaction between pathogen, host and the surrounding environment determines the outcome. Effective organic crop protection requires altering the soil environment and caring for the crop in ways that favor beneficials and suppress pathogens. Growers can promote healthy soil ecosystems by adding carbon with cover crops, compost and organic fertilizers. Following nutrient management plans based on soil and leaf tests will provide the nutrition needed to support vigorous growth and systemic resistance to biotic stress. Finely tuned nutrient management and pathogen suppressive soils will bolster crop growth and maximize the plants’ innate ability to ward off pests and disease.
Eryn Wingate is an agronomist with Tri-Tech Ag Products Inc. in Ventura County, Calif. Eryn creates nutrient management plans for fruit and vegetable growers to improve yield and crop quality while promoting soil health and environmental protection.
1. Chandrashekara, C. & Kumar, Ravinder & Bhatt, J.C. & Kn, Chandrashekara. (2012). Suppressive Soils in Plant Disease Management. 10.13140/2.1.5173.7608.
2. Christos Dordas. Role of nutrients in controlling plant diseases in sustainable agriculture. A review. Agronomy for Sustainable Development, Springer Verlag/EDP Sciences/INRA, 2008, 28 (1), pp.33-46. ffhal-00886444f.
3. Gupta N., Debnath S., Sharma S., Sharma P., Purohit J. (2017) Role of Nutrients in Controlling the Plant Diseases in Sustainable Agriculture. In: Meena V., Mishra P., Bisht J., Pattanayak A. (eds) Agriculturally Important Microbes for Sustainable Agriculture. Springer, Singapore. https://doi.org/10.1007/978-981-10-5343-6_8.
4. Huber, D.M & Haneklaus, Silvia. (2007). Managing nutrition to control plant disease. Haneklaus / Landbauforschung Völkenrode. 4.
5. Vallad, Gary & Goodman, Robert. (2004). Systemic Acquired Resistance and Induced Systemic Resistance in Conventional Agriculture. Crop Science – CROP SCI. 44. 10.2135/cropsci2004.1920.
Growing hemp was outlawed in 1970, but since the California Hemp Farming Act was signed into law and became effective on January 1, 2017, hemp is again a legal crop. Still, not just anyone can throw their hat in the ring to legally grow hemp. There is a somewhat involved registration process to wade through first, as well as rules and regulations for California hemp growers to follow. Here’s a brief overview.
Farmers wishing to grow hemp must pay a $900 fee and apply for registration with the agricultural commissioner in the county where they plan to grow the crop. A separate registration is required for each county in which a grower wishes to produce hemp. Besides detailed contact information, the application must also include the legal description of land that will be used for growing or storing hemp along with the GPS coordinates and a map. Growers must list the hemp cultivars they intend to plant along with the state or country of the cultivar’s origin. They must also describe a plan for testing their plants as well as a proposal to destroy any plants with a THC level above 0.3%. Hopeful hemp growers must also submit a criminal history report.
If a grower’s application is approved, they become a registered grower. The registration is valid for one year. It must be renewed annually at least 30 days before the prior year’s registration expires, and include a $900 renewal fee. Registration and renewal fees may vary from county to county. The ag county commissioners will keep hemp records for at least three years.
If a registered grower wants to change the land area for growing or storing hemp, he must submit an updated registration. The same holds true if he wishes to switch cultivars.
Only approved certified hemp cultivars are allowed. The approved cultivar list may be updated with varieties added, amended or deleted. At least one public hearing will be held before making a change to the list. Only registered agricultural research institutes or registered hemp breeders may legally develop new cultivars.
Sampling hemp plants to test for acceptable THC levels must be done no more than 30 days before harvest. The grower or breeder must be present when samples are collected. Sampling is done by the county ag commissioner or a sample-taker assigned by the commissioner.
Each primary sample will include all parts of the plant—stems, stalks, flowers, buds and seeds, if applicable. Five or more primary samples make up one composite sample which will be taken from each field or from each cultivar within the same field. Indoor and outdoor growing areas are treated as separate fields. Check with the California Department of Food and Agriculture (CDFA) for exact testing procedure, including the number of plants to be tested per field and the portion of the plant that is tested.
Samples, along with the grower’s proof of registration and other documents, are sent to a laboratory approved by the CDFA. The lab must use approved testing methods. The percentage of THC is measured on a dry-weight basis.
The samples will receive a pass or fail report— a pass if the test shows 0.3% THC or less. The grower will receive at least 10 copies of a pass report. The lab keeps report records for two years or more. Growers are required to do the same and must make reports available to the CDFA, the commissioner or law enforcement if asked.
If the plant samples fail with levels over 0.3% but not over 1%, the grower will submit additional samples. If the crop sampling fails a second time, the plants must be destroyed.
The amount of time given for growers to destroy the crop depends on the THC level. If levels fall between 0.3 and 1% THC, plant destruction needs to happen as soon as possible, with growers given a time frame of no more than 45 days after receiving a failed lab report. If plant samples fail with a THC level over 1%, destruction of the crop must begin within 48 hours and be completed within a week.
Exceptions for higher THC levels may be authorized for a registered and established research institute for approved hemp cultivar breeding purposes.
Violations and Consequences
A first-time offender is given a chance to redeem their mistake. If a hemp grower, breeder or researcher commits a negligent violation that is not considered a repeat offense, a corrective plan is put into place by the CDFA secretary. The plan will include a reasonable date to correct the violation.
Once a grower, breeder or researcher is negligent, he is put on a sort of probationary status. For at least the next two years, he must periodically report to the secretary and verify his compliance.
Three strikes and you’re out: If a hemp grower, breeder or researcher commits a negligent violation three times within a five-year span, he is ineligible to take part in the hemp-growing program for five years after the date of his third violation.
Violations deemed intentional, reckless or grossly negligent will be immediately reported by the secretary to the U.S. Attorney General and the California Attorney General.
Anyone who has been convicted of a felony on or after Jan. 1, 2020, which involves a controlled substance under either state or federal law, cannot take part in the California Industrial Hemp Program for 10 years after the date of conviction.
Thou shalt not lie: Anyone who falsifies information on the application or registration is not allowed to take part in the California industrial hemp program.
Hemp Advisory Board
The Industrial Hemp Advisory Board is made up of 13 members, including five registered hemp growers, two agricultural researchers, one representative from the State Sheriffs’ Association, one county ag commissioner, one representative of the Hemp Industries Association, two representatives of businesses that sell industrial hemp products and one member of the public.
The board advises the CDFA on things such as annual budgets, industrial hemp seed law and regulations, enforcement and setting fees. Board members serve a three-year term. That term for current board members runs through May 31, 2023. The board meets at least once a year. Positions are not salaried, but board members may be compensated for travel expenses.
A Look at the Numbers
As of July 2, 2020, there were 553 registered industrial hemp growers and breeders in the state; 1,077 registered cultivation or research sites; and 26,226.3 registered acres.
Leading counties include Riverside with 101 growers and breeders, 152 sites and 8,191.5 acres; San Diego with 78 growers and breeders, 130 sites and 509 acres, and Fresno with 48 growers and breeders, 97 sites and 2,200 acres.
Other counties have fewer growers than those mentioned above, but more than 2,000 acres each in hemp production: Kern County with 2,287 registered acres, Ventura with 2,583 and San Bernardino with 2,763 acres.
Although CBD oil is the prize most hemp growers currently have their eye on, there are an estimated 25,000 uses for hemp – from building materials and biodegradable plastics to rope, sailcloth, cosmetics, clothing, and paper. Hemp has been around for centuries. President George Washington grew utility hemp on his farm; the rough draft of the Declaration of Independence is rumored to be written on paper made from hemp.
In the U.S., hemp was a growing concern during the 19th and into the mid-20th century. In 1970, hemp was outlawed, and shortly afterward most of the hemp research work done by US universities was destroyed. With the passing of the 2018 farm bill, hemp was once again legalized at the federal level, so western universities such as UC Davis and Oregon State University have again formed hemp research programs. Soon there will be a vast network of land lab research results available to assist farmers in hemp cultivation.
OSU had a hemp research center from the 1880s until the 1930s, back when the university was Oregon Agricultural College. After shuttering the program for decades, a new hemp research department, The Global Hemp Innovation Center, has reorganized. The program has 10 research sites around the state, and partners with four research centers in Asia and Europe with similar climates.
OSU has also launched seed certification services for hemp. The certified seed is planted by farmers registered with the state. OSU is the only university in the nation to certify hemp seed. Currently in Colorado, North Dakota, and Tennessee, only state departments of agriculture certify hemp seed for use in each of those individual states.
Oregon’s location on the 45th parallel makes for ideal hemp-growing conditions. Hemp production is rapidly expanding in the state. In 2018, there were approximately 7,000 acres planted in hemp. In 2019 that number grew to approximately 50,000 acres, edging out Montana and Colorado. Estimates put Oregon in first place in US hemp production. Oregon CBD growers are aiming for 500,000 acres of seed sales by 2021—a $1 billion yield.
But California is closing the gap. With labor and growing costs continuing to rise in the state, many California farmers are turning to hemp as a go-to crop. And the race to be the leading state in hemp production is on.
UC Davis Research
The California Hemp Corporation, located in Oakdale and formed by Jeff McPhee and Kent Kushar, has partnered with UC Davis to study hemp growth in the California Central Valley. The team wants to help turn the Central Valley into the hemp capital of the country. McPhee predicts hemp production will “change California.”
Director of the Plant Breeding Center, Professor Charlie Brummer is leading the research project at UC Davis, which was launched in 2019. Dan Putnam is the head of field testing. The project, which is breaking new and significant ground in the UC system, aims to gather data to help farmers successfully grow hemp in the California Central Valley. The intention is to create a significant hemp breeding program, “for what may be the most important crop in a generation,” Brummer said on the research website.
Associate Professor Li Tian, Co-Director of the UC Davis Cannabis and Hemp Research Center, was appointed to the position in January 2020. She is looking forward to diving into the brand-new research and being part of the role the university can play in assisting the industry. Tian’s research focuses on how natural chemicals with benefits for human health, phytonutrients, are created and controlled within plants.
About hemp, Tian said, “This is such a new industry in California and nationally, so it’s really exciting to apply our expertise to studying this crop.”
Tian has been reaching out to the other UC campuses with shared research interests. The university system is looking at how air temperature and other growing conditions affect crop yield. Researchers are also looking into the regulation of hemp production, the agronomy, and the environmental impact.
“We still need a lot of research,” Tian said.
COVID-19 has somewhat affected the program. Tian said when Governor Newsom’s stay-at-home order came, the university team couldn’t entirely stop their research and risk losing all that work. But the researchers did reduce their activity, along with the scale and intensity, strictly following the state, local and university guidelines, she said.
Plants to Products
Another new research program through the Department of Plant Sciences at UC Davis is Cannabis and Hemp –Plants to Products. The program is led by Professor Gail Taylor. Researchers are looking into the potential of hemp and cannabis.
“We are focused on molecular and traditional approaches to genotyping, phenotyping, pre-breeding and breeding for bespoke chemical signatures that may be of value to the pharmaceutical and other industries,” the team states on their website. “We have expertise to address the environmental impact of cannabis and hemp cultivation, particularly water, pest, pathogen and greenhouse gas impacts, and can offer advice on minimizing these environmental footprints.”
The team is open to inquiries from outside agencies who wish to partner with them. One such partner is Biopharmaceutical Research Company.
“It’s really in its infancy,” Biopharmaceutical Research Company CEO George Hodgin said of the cannabis industry. “Crops like apples and strawberries and bananas have such a long history of research.”
Hodgin said the main thrust of their research business is providing federally legal cannabis to federally approved researchers, both for university and medical research. Cannabis regulatory requirements are often challenging hoops to jump through, so Hodgin’s business model assists with that.
California hemp growers are required to have a DEA-licensed laboratory test their product two weeks before harvest to make sure CBD levels are low enough. If the levels are too high, the crop must be destroyed. Biopharmaceutical Research Company provides DEA and USDA compliant hemp processing services to California hemp growers.
Even if California doesn’t bump Oregon out of the number one spot in hemp-acreage production, hemp grown in hot and dry weather regions like SoCal does tend to produce higher levels of CBD.
CBD levels were down in the Pacific Northwest and other areas around the country in 2019 crops, according to James Knox, owner of KLR Farms. KLR is a multi-state business, headquartered in Albany, Ore. Knox’s operation grows hybridized and feminized hemp seed and ships worldwide. There was a 24-35 percent depreciation in CBD content last year in most regions, Knox said. However, CBD levels in SoCal grown hemp crops were up.
Growers’ programs for hemp farmers are also cropping up. In 2019, a team of experienced researchers, growers and business professionals formed the Imperial Valley Hemp and CBD Program (IV Hemp) to facilitate the success of hemp growers in SoCal and surrounding areas.
IV Hemp is a co-op designed to help farmers successfully grow, harvest and sell hemp “from seed to sale.” The grower’s program offers special seed prices to farmers who grow through the program. Among other benefits is a partnership with a CBD oil extraction facility in the Imperial Valley and help with biomass transport, if needed.
Even though cannabis research is once again new, hemp production isn’t waiting – it continues to expand. An analytics firm called the Brightfield Group is tracking the cannabis industry. According to their data, the CBD market is expected to grow from $618 million in 2018 to $22 billion by 2022.
Soilborne diseases can cause devastating damage to strawberries. Most soilborne pathogens are lethal to this crop; fungal pathogens in the soil infect plants via roots and can impact the ability of the plant to uptake nutrients and water, causing a wilt symptom in leaves and stems in the early- to mid-harvest period. Fruit yield of infected plants is severely reduced, and the plants often die off eventually. Other soilborne pathogens, known as “root nibblers,” do not kill plants, but stunt them and likewise reduce fruit yield.
Soilborne disease management in organic strawberry production is a challenge. Unlike conventional strawberry production, no fumigants are available, tools are limited and soilborne pathogens are spreading, especially in California. However, recent studies provide some potential approaches and hints for developing agroecological management strategies.
Described in this article are three lethal soilborne pathogens commonly found in strawberry production in California. Then four approaches to managing these pathogens in organic strawberry systems are discussed.
Know Your Enemies
Table 1 shows three common lethal soilborne diseases and the responsible pathogens in California strawberries. Verticillium wilt caused by Verticillium dahliae is a classic soilborne disease in strawberries. The disease was first reported in 1932 in California strawberries and was the most widespread soilborne disease in the state until recently. Methyl bromide + chloropicrin chemical fumigation was developed to control this disease in the 1950s. In the late 2000s, however, two other soilborne diseases emerged: Fusarium wilt caused by Fusarium oxysporum f. sp. fragariae (F.o.f.) and charcoal rot caused by Macrophomina phaseolina. These pathogens were first reported in the southern production region and are now spread across the entire state, becoming a larger threat to the California strawberry industry.
These three pathogens have different characteristics (Table 1). First, the plant hosts differ between the three fungi; V. dahliae is known to infect more than 400 plant species, including 100 weed species, whereas F.o.f. and M. phaseolina (Koike et al., 2016) only infect strawberries. Second, the soil survival period varies; V. dahliae can survive in the soil without a host plant for an extended period (8-10 years) compared to F.o.f. and M. phaseolina (< 3 years.) Third, F.o.f. and M. phaseolina can survive in soil as saprophytes, meaning that these pathogens can feed not only on living plants but also can colonize dead organic matter such as crop residues and some organic amendments (e.g., rice bran, almond shell.) In contrast, V. dahliae does not have the ability to persist in soil as a saprophyte.
Understanding the characteristics of pathogens, the enemies, is crucial for developing a soilborne disease management strategy in organic strawberry production, as discussed below.
Diagnosing the Pathogen
If there are any symptomatic plants in your organic strawberry field, the first step in disease management is to determine the primary cause of symptomatic plants. Since each pathogen has different characteristics as mentioned above, it is vital to identify the specific pathogen(s) causing the wilt symptom. Unfortunately, wilt symptoms caused by these three soilborne pathogens are almost identical, and confirmation by visual observation is impossible even with the eyes of well-trained plant pathologists (see figure 1). Fortunately, recent developments in molecular approaches are making rapid and accurate determination of plant pathogens a reality.
This advance in pathogen identification is available for strawberry plant samples. The molecular method for identifying all three pathogens mentioned above in plants is now available at public and commercial plant pathology labs. The analysis can be done in a matter of hours.
The molecular test for soil samples is becoming available as well. For soil tests, however, not only is a quick and accurate detection method needed but also an economic threshold number above which crop yield decreases. At this time, among the three pathogens, V. dahliae is the only one for which both the molecular-based quantitative method and the threshold are developed. For M. phaseolina, a quantitative molecular approach has been established but no threshold developed. For F.o.f., only a qualitative molecular test is available and no threshold has been set. Active research is in progress in creating rapid and effective soil tests for these and other soilborne pathogens.
Organic Management Practices
Once the pathogen is identified, the next step is to develop an appropriate management strategy. Described here are four organically acceptable practices that can be implemented to mitigate soilborne diseases: crop rotation, anaerobic soil disinfestation, the use of varieties resistant to these diseases and sanitation practices.
Crop rotation: Crop rotation is a traditional method used worldwide to avoid soilborne diseases in strawberries and other crops. By planting different crops sequentially in a field, the temporal crop diversity, rather than spatial crop diversity, of the field is increased. Since each crop encourages the growth of specific soilborne pathogens and microorganisms in the rhizosphere, this practice enhances diversity in the soil microbial community and reduces the populations of plant-specific soilborne pathogens. In the organic systems in the U.S., crop rotation is mandatory under the National Organic Program. In the E.U., Northeast U.S. and Canada, a minimum of a three-year break between two strawberry plantings on the same field is recommended.
In California organic strawberries, back in the 1990s, crop rotation with at least a three-year break between each strawberry planting was the only approach used to avoid soilborne diseases. This strategy works best for soilborne pathogens that only infect strawberries (e.g., F.o.f. and M. phaseolina.) Anecdotal evidence indicates that at least a two-year break is necessary to avoid or reduce Fusarium wilt in strawberries on the central coast of California.
However, the long break period itself is not enough to suppress soilborne pathogens hosted by multiple plants. V. dahliae is the prime example of this challenge. For managing this pathogen, avoiding non-strawberry host plants during the break period is essential. Table 2 provides examples of host and non-host crops of V. dahliae, which highlights some major vegetable crops in California that are hosts of this pathogen. Further, about 100 weed species, including shepherd’s purse, dandelion, groundsel, nightshade and pigweed, also host this pathogen and make weed management an integral part of the soilborne disease strategy.
The good news is that studies found some crops actually suppress these pathogens. The effect of broccoli residue incorporation on suppressing V. dahliae in the soil is well-documented (Subbarao et al., 2007). After harvesting heads, leaves and stems are flail mowed and incorporated into the soil; breakdown of the broccoli residue results in a lowering of V. dahliae soil populations. This is a long-term strategy, and two or more broccoli crops may be necessary to start reducing the V. dahliae population in a highly infested field.
Preliminary studies by two independent labs showed that a specific variety of wheat appears to suppress M. phaseolina in the soil. A greenhouse study demonstrated that when strawberries were planted after growing different wheat varieties in soil infested with M. phaseolina, the variety Summit 515 was the most effective in suppressing this pathogen (Ivors, 2015). The practice is being used by some commercial growers and observationally seems to have an effect.
Recent studies from Asian countries demonstrated that Allium crops such as leeks and onions were effective in suppressing Fusarium oxysporum in spinach (Igarashi et al., 2017) and bananas (Huang et al., 2012). The biological mechanism of this suppression was also elucidated (Nishioka et al., 2019). A preliminary field trial in California is in progress to examine the effect of this approach in suppressing F.o.f. in strawberries.
Anaerobic soil disinfestation: Another tool for organic strawberry growers is a practice called anaerobic soil disinfestation (ASD.) ASD as a biological alternative to fumigation was developed independently in both the Netherlands and Japan around the year 2000. ASD creates the acid fermentation process in anaerobic soil in which toxic organic acids, volatiles and Fe2+ ions are produced, and microbial community shifts subsequently take place. This biologically mediated process suppresses a range of pathogens and nematodes in the soil. Over the last 15 years, ASD was examined extensively in California strawberry systems and proved to be effective in suppressing a range of soilborne pathogens. Today, over 1500 acres of organic berry fields in California are treated by ASD.
The standard ASD process involves multiple steps (seefigure 2). During the ASD treatment, a total of approximately 1.5 acre-inches of water is applied via drip irrigation. After the treatment, planting holes are cut, and transplants are planted after one week. Both the level of anaerobic conditions (the stronger, the better) and soil temperatures (the warmer, the better) are keys for a successful ASD.
The three lethal soilborne pathogens each respond differently to ASD. In coastal California, ASD can suppress V. dahliae well under typical fall temperatures (Shennan et al., 2018). For F.o.f., however, ASD must be done in summer using clear plastic mulch. Using this approach, a study found a threshold of >460 hours above 86 °F at eight-inch soil depth is needed to suppress this pathogen on the central coast of California (Muramoto et al., 2020).
ASD should never be applied in the fall in coastal California to fields with a known history of Fusarium wilt. This saprophytic pathogen can grow on rice bran and result in increased populations under a lower soil temperature. This often results in higher levels of Fusarium wilt (see figure 3). Results on the effect of ASD on M. phaseolina are mixed so far, and more research is needed.
Resistant varieties: The use of resistant varieties can be the easiest and most reliable approach for a specific soilborne disease. Information on the level of soilborne disease resistance of the UC varieties is available at the California Strawberry Commission’s website calstrawberry.com/en-us/Pest-Management/Breeding. Note that there is no single variety that is resistant to all three soilborne pathogens. Also, currently there is a lack of a M. phaseolina resistant variety and a public variety with both excellent flavor and Fusarium wilt or charcoal rot resistance.
Sanitation practices: Basic sanitation practices such as washing soil off from tractors, equipment and tools are also critically important to avoid spreading soilborne pathogens. Sanitation and prevention are the key tools in soilborne disease management in organic strawberry production.
Integrated Disease Management
Soilborne disease management in organic strawberries requires an integrated approach. Based on the level and type of pathogens identified, or from the disease history of the site, a grower needs to develop an appropriate soilborne disease management strategy for the site by integrating available practices such as crop rotation, ASD and use of a resistant variety as well as basic sanitation of machines and tools to prevent the spread of soilborne pathogens from one field to another.
Well-designed crop rotation is the foundation of soilborne disease management in organic strawberry production. Diversified organic growers who grow strawberries as a core crop among many other crops may want to design their crop rotation around strawberries, one of the most soilborne disease-prone and lucrative crops. Specialized organic strawberry growers might not be able to control the crop rotation by themselves, but it is worth communicating with the vegetable grower with whom they rotate the field.
ASD is a useful tool when there is no choice but to plant strawberries after a Verticillium host crop such as lettuce. A resistant variety can be chosen as needed when it is acceptable for your market.
Tools for soilborne disease management in organic strawberries are still limited. Interactions between a crop plant and its microbiome, including pathogens and beneficial microbes, need to be better understood, and differences in microbiomes between varying crops need to be discovered. Armed with such science-based information, improved suppressive crop rotations may be able to be developed as well as ways to use microbial amendments more effectively. This soilborne disease management approach is knowledge-intensive and location-specific, which is in contrast with fumigation practices that are characterized by chemical-intensive and location-general approaches.
Acknowledgements: The author would like to thank valuable comments from Steve Koike, Kelly Ivors, Mark Bolda and Erin Foley to the previous version of the manuscript.
Igarashi, C., Asano, Y., Nishioka, T., Suga, H., Hyakumachi, M., Shimizu, M., 2017. Suppression of spinach Fusarium wilt by intercropping with Allium plants. Japanese J. of Phytopathology 83, 87-94.
Koike, S. T., Arias, R. S., Hogan, C. S., Martin, F. N., and Gordon, T. R. 2016. Status of Macrophomina phaseolina on strawberry in California and preliminary characterization of the pathogen. Int. J. of Fruit Sci. 16: 148-159.
Muramoto, J., Shennan, C., Mazzola, M., Wood, T., Miethke, E., Resultay, E., Zavatta, M., Koike, S.T., 2020. Use of a summer cover crop as a partial carbon source for anaerobic soil disinfestation in coastal California. Acta Hort. 1270, 37-44.
Nishioka, T., Marian, M., Kobayashi, I., Kobayashi, Y., Yamamoto, K., Tamaki, H., Suga, H., Shimizu, M., 2019. Microbial basis of Fusarium wilt suppression by Allium cultivation. Scientific Reports 9, 1715.
Shennan, C., Muramoto, J., Koike, S., Baird, G., Fennimore, S., Samtani, J., Bolda, M., Dara, S., Daugovish, O., Lazarovits, G., Butler, D., Rosskopf, E., Kokalis-Burelle, N., Klonsky, K., Mazzola, M., 2018. Anaerobic soil disinfestation is an alternative to soil fumigation for control of some soilborne pathogens in strawberry production. Plant Pathology 67, 51-66.
Subbarao, K.V., Kabir, Z., Martin, F.N., Koike, S.T., 2007. Management of soilborne diseases in strawberry using vegetable rotations. Plant Dis. 91, 964-972.
Managing arthropod pests with pesticides is a common practice in crop production. Managing arthropod resistance to pesticides is an important part of integrated pest management (IPM.) Under natural circumstances, plants, insects, mites, natural enemies and beneficial or harmful microorganisms continuously co-evolve and adapt to the changes in their environment. When there is a higher selection pressure, such as the indiscriminate use of pesticides, mutations in arthropods enable them to resist the pesticide and increase their chances of survival. Since there are fewer pesticides for organic crop production, there is a higher chance of their repeated use and increased risk of resistance development.
Arthropods, such as insects and mites, develop resistance to chemical pesticides through genetic, metabolic, or behavioral changes resulting in reduced penetration of toxin, increased sequestration or excretion, reduced binding to the target site, altered target site that prevents binding of the toxin, or reduced exposure to the toxin through modified behavior. Through one or more of these mechanisms, arthropods can also develop resistance to biopesticides. When the active ingredient of a biopesticide is a toxic molecule and acts more like a chemical compound, arthropods are more likely to develop resistance even though it is of biological origin. When the mode of action is due to infection by a microorganism, rather than a toxin, arthropods are less likely to develop resistance.
Botanical Pesticide Resistance
Botanical insecticide pyrethrum, extracted from the flowers of Chrysanthemum cinerariaefolium and C. cineum, contains insecticidal esters known as the pyrethrins. Pyrethrins are nerve poisons disrupting the sodium channels in neurotransmission and are commonly used for controlling pests in agricultural, structural and public and animal health sectors. Arthropod resistance to pyrethrins and their synthetic analogs, pyrethroids, is very common and has been reported for several decades. Insect mutations that reduce the penetration of the toxin through the cuticle, reduce its binding to the target site, or alter the properties of the sodium channels, and other mechanisms impart pyrethrin resistance.
Another botanical insecticidal compound, azadirachtin, is a tetranortriterpenoid limonoid from neem (Azadirachta indica) seeds, which acts as an insecticide, antifeedant, repellent and insect growth regulator. While neem oil, which has a lower concentration of azadirachtin, has been used in the United States as a fungicide, acaricide and insecticide for a long time, several azadirachtin formulations in powder and liquid forms have become popular in recent years. While there was a report of artificially induced resistance to azadirachtin in the green peach aphid, several studies demonstrated the efficacy of azadirachtin against various pests and recommended it as an option in IPM and for managing resistance to other pesticides. Azadirachtin is also thought to reduce the production of detoxification enzymes and known to improve the efficacy of other biopesticides. While arthropod resistance to botanical pesticides other than pyrethrins is not commonly reported, it is known that plant allelochemicals (e.g. alkaloids, phenolics, terpenoids, etc.) can contribute to cross-resistance to certain chemical pesticides. It is important to monitor the potential risk of resistance development and cross-resistance when botanical pesticides are used.
Bacterial Biopesticide Resistance
Bacillus thuringiensis (Bt) is a gram-positive soil bacterium, which contains crystalline toxic protein that is activated upon ingestion by an insect host, binds to the receptor sites in the midgut, and eventually causes insect death. Bt pesticides are used against a variety of lepidopteran (Bt subsp. aizawai and Bt subsp. kurstaki), dipteran (Bt subsp. israelensis and Bt subsp. sphaericus) and coleopteran (Bt subsp. tenebrionis) pests and are very popular in organic farming. Since the mode of action involves toxins rather than the bacterial infection itself, resistance to Bt pesticides or transgenic crops that contain Bt toxins is also very common. Some examples of resistant insects to Bt include the beet armyworm, the cabbage looper, the corn earworm, the Colorado potato beetle and the diamondback moth. Mutations in insects that regulate the immune system or interfere with the activation of Bt toxins and their binding to the target site led to insect resistance.
Spinosad is a mixture of macrocyclic lactones, spinosyns A and spinosyns D, derived from Saccharopolyspora spinosa, an actinomycete gram-positive bacterium, and is used against dipteran, hymenopteran, lepidopteran, thysanopteran, and other pests. Although naturally derived, some spinosad products are not registered as biopesticides. Insect resistance to spinosad later led to the development of spinetoram, which is a mixture of chemically modified spinosyns J and L. Both spinosad and spinetoram are contact and stomach poisons and act on insect nervous system by continuous activation of nicotinic acetylcholine receptors. The American serpentine leafminer, the beet armyworm, the diamondback moth, the tomato borer, the onion thrips, and the western flower thrips are some insects with spinosad resistance. Production of detoxifying enzymes (metabolic resistance) and changes in the target site are the most common mechanisms of spinosad resistance in insects. Cross-resistance between spinosad and some chemical insecticides has also occurred in some insects.
Viral Biopesticide Resistance
Baculovirus infections in Lepidoptera have been known for centuries, especially in silkworms. Currently, there are several commercial formulations of nucleopolyhedroviruses (NPV) and granuloviruses (GV). When virus particles are ingested by the insect host, usually a lepidopteran insect, they invade the nuclei of midgut, fatbody, or other tissue cells and kill the host. Baculoviruses are generally very specific to their host insect species and can be very effective in bringing down the pest populations. However, variations in the susceptibility of certain insect populations and development of resistance to viruses has occurred in several host species. Mutations in one or more genes with complex mechanisms are involved in insect resistance to viruses.
Fungal Biopesticide Resistance
There are several fungi that infect insects and mites. The fungal infection starts when fungal spores come in contact with an arthropod host. First, they germinate and gain entry into the body by breaching through the cuticle. Fungus later multiplies, invades the host tissues, kills the host and emerges from the cadaver to produce more spores. Entomophthoralean fungi such as Entomophthora spp., Pandora spp., and Neozygites spp. can be very effective in pest management through natural epizootics, but cannot be cultured in vitro for commercial-scale production. Hypocrealean fungi such as Beauveria bassiana, Isarea fumosorosea, Metarhizium brunneum and Verticillium lecanii, on the other hand, can be mass-produced in vitro and are commercially available. These fungi are comparable to broad-spectrum insecticides and are pathogenic to a variety of soil, foliar and fruit pests of several major orders. Since botanical, bacterial and viral biopesticides have insecticidal metabolites, proteins, or viral particles that have specific target sites and modes of action, insects have a higher chance of developing resistance through one or more mechanisms. Although fungi also have insecticidal proteins such as beauvericin in B. bassiana and I. fumosorosea and dextruxin in M. anisopliae and M. brunneum, their mode of action is more through fungal infection and multiplication, and arthropods are less prone to developing resistance to entomopathogenic fungi. However, insects can develop resistance to entomopathogenic fungi through increased melanism, phenoloxidase activity, protease inhibitor production and antimicrobial and antifungal peptide production. It also appears that the production of detoxification enzymes in insects against fungal infections can also impart resistance to chemical pesticides.
These examples show that insects can develop resistance to biopesticides in a manner somewhat similar to chemical pesticides, but due to the typically more complex and multiple modes of action, at a significantly lesser rate depending on the kind of botanical compound or microorganism involved. Resistance to entomopathogenic fungi is less common than with other entomopathogens. The risk of biopesticide resistance is much higher in organic farming because of the widespread use and limited biopesticide choices. Avoiding the repeated use of biopesticides reduces the risk of resistance development and can reverse the resistance mechanism in some cases. IPM recommends the use of host plant resistance, biological control, cultural control and other management options before using pesticide applications. When pesticides (both biological and synthetic) are to be considered, using them only when needed, applying at recommended rates and alternating/rotating with other modes of action can reduce the selection pressure on arthropod populations and resulting mutations.