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Biocontrol Agent Failures Can be Linked to Past Pesticide Applications

Thu, Mar 23rd, 2023, created by Thomas Ford
Vegetable production in protected culture systems is growing exponentially in many communities as the demand for local year-round produce increases. High tunnel and greenhouse-based production systems present different challenges for growers, but they both can be a source of great frustration when pest issues emerge.

Most new entrants into vegetable production in protected culture systems are experienced vegetable producers that are experts when it comes to managing pests in the field. When these growers move vegetable  production indoors per se they realize almost immediately that their field-based approaches to pest management will not work well in the confines of a high tunnel or greenhouse. Once this realization takes place some field-based growers will try to unsuccessfully meld their field-based pest management techniques with bio-based control practices with often disastrous results.

Several months ago, I entered into a discussion with a new greenhouse vegetable grower who released and quickly killed hundreds of dollars of biocontrol agents. He worked with a reputable biocontrol agent supplier and released the appropriate biocontrol agents for managing an assortment of pests (aphids, whiteflies, two-spotted spider mites, etc.) . This grower never disclosed to the biocontrol agent supplier that he had applied an assortment of pesticides in the greenhouse (some of them off-label) to the tomato crop prior to the release of the biocontrols. When the biocontrol agents died, he quickly dialed the supplier and filed a complaint about the quality and efficacy of the biocontrol agents that he had purchased even though it was his pesticide usage that was clearly responsible. This grower did not realize that pesticide residues can persist for a very long time in the greenhouse environment and that their past usage may jeopardize the health and vigor of even the most robust biocontrol agent.

If you are a new greenhouse or high tunnel vegetable grower you need to be aware of the potential impact of pesticide residues on biocontrol agents. When selecting pesticides for use with biocontrol agents you must cross-reference every active ingredient in the pesticides that you wish to deploy with their potential side-effects to the bicontrol agents that you wish to release. Pesticides that have no adverse side effects should be the primary materials in your chemical arsenal if you are going to deploy biocontrol agents in your greenhouse or high tunnel. Biorational insecticides like horticultural oil and insecticidal soap are two broad-spectrum insecticides that can be used safely prior to the release of most bicontrol agents in the greenhouse and high tunnel.

If you are considering transitioning to a bio-based pest management system compile a list of the pest and disease management products that you have applied within the last 6 months in the production environment. Cross reference each product with one of the industry-produced side-effect manuals or share your list of pest and disease management products with your bicontrol agent supplier to receive their counsel. When confronted with pesticide persistence in the production area a grower may be forced to:
Delay the release of biocontrol agents into the production environment due to pesticide persistence.
Increase your stocking rate of biocontrol agents in the production area to account for increased mortality due to the persistence of pesticide residues in the growing environment.
Switch to a different biocontrol agent that can better tolerate the pesticides that have been applied in the production area.
Abandon the usage of biocontrol agents for this production season and resume using chemical pesticides to manage pests for the immediate future.

For additional information on utilizing biocontrol agents in protected culture systems with vegetable crops please contact the author or reach out to your local Extension Educator.

About the Author:

Thomas Ford

Commercial Horticulture Educator, Penn State Extension

Tom has worked for over 40 years with Cooperative Extension in Maryland, North Carolina, and Pennsylvania. During his career he has worked intensively with vegetable and fruit growers, greenhouse and nursery operators, landscape and turf professionals and area farmers with their production and pest management issues.


Tom is a native of Central Maryland and resides with his wife, Laura and their four sons in Duncansville, PA. Tom has a B.S. degree in Ornamental Horticulture from the University of Maryland and a MBA from Frostburg State University in Frostburg, MD. Tom currently serves as a Commercial Horticulture Educator with Penn State Extension and is housed in the Cambria County Extension Office in Ebensburg, PA.

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