Pesticides are expensive and should only be used when needed.

“Pesticides are not always needed and should be only used when necessary using the correct product for the correct pest at the correct developmental stage for a specifically identified pest,” Bethke said. “Follow the label. If you apply at a higher label rate you’ll have a greater chance of developing insecticide resistance.”

Pesticides can fail to control pests but usually the real culprit is human error. The most common human mistakes include the failure to implement an IPM program, a failure to monitor, misidentification of pests, incorrect pesticide application rates, pesticide resistance, and using old products.

“Some growers have a cabinet of old pesticide materials. These products will not work,” Bethke said. “Pesticides stored in hot areas degrade over time.”

Another reason pesticides fail is due to the water used in tank mixes. “Water is huge,” Bethke said. “Most pesticides work better if the water is acidic.”

Greenhouse plant production incorporates many plants grown in tight quarters. It is more difficult to effectively cover plants with pesticides. A successful tool to improve pesticide performance is the use of adjuvants.

“Insecticides, including the product Abamectin for mite control, work better and for a longer period of time with an adjuvant,” Bethke said.

Adjuvants can enhance the consistency of pesticides thereby reducing pesticide roll off from the plant to the floor.

Another reality of greenhouse farming is insects mature faster due to higher temperatures in the facility.

Bethke also stressed the importance of pesticide rotation to reduce pest resistance by using various modes of action (MOA). MOA information is available from the Insecticide Resistance Action Committee online at