Organic pest management is not a one size fits all cure

Originally published in Issue 14

If you want a recipe for how to specifically control insect pests, then you would best be served using conventional chemical pest management.

“When you look at things through an organic lens, it’s all about context,” said Michigan State University entomologist Matt Grieshop. “There are options to choose from, but your pest management choice is going to be dictated by your specific needs and circumstance. What works for one grower may not work for another for a whole host of reasons. You have to educate yourself about the system.

“It’s not as simple as putting a chemical in a tank and spraying. That is a very successful form of agriculture, but it is completely contrary to the philosophy of an organic system.”

Grieshop said there are two misconceptions when it comes to organic insect control.

“The average person on the street thinks that organic pest management is something that takes care of itself and growers don’t have to do anything. Which is absolutely bogus,” he said. “You are building a system that nature never would have thought up and that would never work in nature. Nature doesn’t work the way that agriculture works. So you are always going to have pest management issues of some sort. You’re going to have to do something.”

The second misconception about organic insect control is there are an infinite number of replacements to manage whatever pests growers may encounter.

“There are insect pests in Michigan that we struggle with every year just because we don’t have good control tools for them,” Grieshop said. “Pesticides exist because agriculture is unnatural and pests are inherently difficult to manage, especially on fresh produce.

“The tools for organic production are limited. You have to supplement that tool set with a lot of intelligence and experience. It is complicated and that is why not everyone is an organic grower. If it was easy, everyone would do it.”

Grieshop said organic pest management is not a one size fits all cure. That is chemical agriculture.

“The thinking behind chemical agriculture is I can grow whatever I want, wherever I want, whenever I want and to accomplish that all I have to do is apply a lot of petrochemicals and high energy inputs to make the system do what I want,” he said. “If I have a problem, I’ll spray with a chemical and kill what needs to be killed. In organic agriculture, it’s really about growing the right thing in the right space at the right time. This means you have to know more about what you are doing. If you know that you have a high incidence of an insect pest or a disease, then you choose a crop and a cultivar that are appropriate for the environment.”

Insect control choices

Grieshop said pest management for organic growers begins with preventive and cultural pest management.

“This means growing the right crop for the environment,” he said. “Choose cultivars that are resistant to your primary pest issues. Use good crop rotation. Try to do everything you can to create a favorable crop environment and an unfavorable pest habitat. If that doesn’t work then you move onto biological and physical inputs.”

Grieshop said for both field crop and controlled environment agriculture situations there are pesticides that are USDA-National Organic Program compliant. Products that are labeled for use on both these types of production systems include:

  • Bacillus thuringiensis used primarily for lepidoptera pests.
  • Spinosad-based products provide good control on soft-bodied insects and Lepidoptera caterpillars. Spinosad is a natural product derived from the soil bacterium Saccharopolyspora spinosa.
  • Neem-derived products provide good control against soft-bodied insects and some pathogenic fungi.
  • Beauvaria bassiana is a soil-borne pathogenic fungus that attacks soft-bodied insects.
  • Nematodes are soil-borne roundworms that are applied to the soil and infiltrate the larvae of thrips and fungus gnats, cut worms and grubs. Grieshop said nematodes make good sense in a small scale system, especially if growers can produce them in-house. Michigan State and Cornell University have made videos on how to raise nematodes.
  • Diatomaceous earth is a mined product that is effective against soft-bodied insects, including snails and slugs. These prehistoric calcium-based microbes have sharp edges that damage an insect’s exoskeleton leading to desiccation.
  • Pyrethrum, a naturally derived chrysanthemum extract, is a broad spectrum, short residual neurotoxin that is effective mostly on soft-bodied insects.


Grieshop said the following controls are best used in greenhouse applications because they tend to disperse unless there is a means to contain them in an insect-infected area.

  • Predaceous mites can be used against thrips and other plant-eating mites.
  • Ladybird beetles are effective against aphids. Grieshop doesn’t suggest using the beetles for field agriculture because they tend to disperse unless there is a means to contain them in an insect-infected area.
  • Lace wings are predaceous on larvae of primarily soft-bodied insects including aphids.
  • Parasitoids and other predators can be purchased for specific insect pests. Grieshop said growers really need to know what insect pests they are dealing with before using these types of controls.

“All of the organic growers I work with actively try to foster biological controls in their plantings,” Grieshop said. “If you avoid spraying a lot of broad spectrum neurotoxins, you’re going to have more insect diversity in your system because you are not killing everything. Other things growers can do are to maintain flowering plants year-round and maintain the soil using cover crops. All of these things promote biodiversity in the production system and promote predaceous and parasitic insects. These practices may also promote pest insects too if growers aren’t sure of what they are doing. Shelter- and plant-based food sources are common resources for both beneficials and pest insects.”

OMRI-certified products

Organic Materials Review Institute (OMRI) is a nonprofit organization that works with input suppliers that service the organic market.

“Manufacturers and suppliers pay OMRI as a third party to certify their products are compliant with the National Organic Program,” Grieshop said. “These products include fertilizers, substrates, food preparation sterilants and pest management controls. Growers can look for the OMRI seal if they are buying organic inputs.

“However, for certified organic growers selling in an organic marketplace, the OMRI stamp does not guarantee 100 percent that the product can be used. Growers must confirm with their organic certifier if an OMRI-certified product can be used. Growers need to talk with their particular organic certifier before they make an application of any input.”

Grieshop said there will be times that a product has the OMRI stamp, but a particular certifier may not agree with an OMRI classification.

“The certifier has the final say on a grower’s farm as to whether or not something can be certified,” he said. “The certifier is not legally required to accept a product’s OMRI certification. However, nothing prevents the grower from going to a different certifier. And this is one of the many reasons growers choose a specific certifier.”

Photo courtesy of Matt Grieshop, Michigan State University Entomology

Comparing controlled environment, field production

Grieshop said controlled environment agriculture has more organic insect control options than field agriculture, but a lot of that has to do with the economics behind the two production systems.

“In a controlled environment such as a greenhouse or vertical farm, production space is considered by the square foot,” he said. “Making an economic decision about a CEA system, boils down to how many dollars is each square foot of production space worth? In a field crop environment, the typical thinking is in dollars per acre (43,560 square feet). Depending on the value of a square foot, in a greenhouse that might be 100 to 200 times more compared to a field-grown crop. That means the greenhouse grower can afford a lot more controls than a field grower.

“If a grower has 1,000 square feet of greenhouse space, and expects to make $50,000 off that space, that’s $50 per square foot of income that he’s protecting. If a grower is producing field corn, he might expect to make $4,000-$5,000 per acre. That is $5,000 over 43,560 square feet. What the field grower can afford to protect is a lot lower.”

If a grower releases biological control agents in a greenhouse, like these predatory mites on raspberries, he has a reasonable expectation that the mites will stay where he wants them to be active. There are no such guarantees in open field production settings.

Grieshop said a second difference in CEA is a greater amount of control over the environment and the control over the space.

“If a grower is going to release biological control agents in a greenhouse, he has a reasonable expectation that they are going to stay where he wants them to be active,” he said. “In an open field there are no such guarantees.

“Those are the two big functional differences. The gross economic value of the system and the ability to change things. Both of those factors essentially give CEA growers insect control options that would never be considered for open field culture. It doesn’t change the availability of those inputs, it just changes whether they are relevant.”

 


For more: Matthew Grieshop, Michigan State University, Department of Entomology, Center for Integrated Plant Systems Bldg.; (517) 432-8034; grieshop@msu.edu; http://www.ent.msu.edu/directory/matthew_grieshop; http://www.opm.msu.edu; http://msue.anr.msu.edu/topic/info/organic_agriculture.

David Kuack is a freelance technical writer in Fort Worth, Texas; dkuack@gmail.com.

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