Insect Management Action Thresholds

The first and most important step in any pest management program is to make sure the pest in question has been correctly identified. Failing to miss this step can cost both time and money and may also contribute to possible crop damage if the wrong treatment is applied. If you are unsure about what insect, weed or pathogen you may be dealing with, the WSU Plant Pest Diagnostic Clinic can help. They can be contacted via email at plant.clinic@wsu.edu or via phone at 509-335-3292.

Once a pest has been correctly identified, next in the management process is the monitoring of the pest population size and threshold assessment. This can be done by using a sweep net or beating tray (if an insect) or by visual inspecting your crop for pathogens or weeds. The “Action”, “Treatment” or “Economic” threshold is the level of a pest population at which the crop is just approaching imminent loss of yield. Another way to think of this level is a pest population density at which control measures should be applied to prevent the population from reaching the economic injury level. The Economic Injury Level is defined as a pest population density at which the financial benefits of control measures are equal to or greater than the control cost.

Action Thresholds for Insect Pests in the PNW

Wireworms

4 or more wireworms per 20 shovels of soil or 1 to 2 wireworms per solar-bait trap.

Hessian Fly

20% of tillers in winter wheat, and 38% of tillers in spring wheat have hessian fly eggs/larvae.

Cabbage Seed Pod Weevil

3 to 4 adult cabbage seed pod weevil’s per 10 sweeps.

Cabbage Aphid

2 per plant at the seedling stage, 5 per leaf at the rosette stage, or when 20 percent of the heads are infested during bloom.

Pea Weevil

1 to 2 adults in 25 sweeps.

If you would like to see what insecticide products are available or compare active ingredients the Insecticide Mode of Action and Comparison tool was developed to help producers identify insecticides based on “Crop” i.e. Wheat, Canola, or Peas, product “Trade Name” by “Active Ingredient” or by the insecticide Mode of Action (MOA).

Whenever you are starting an insecticide program, it is important to be mindful of beneficial insects and pollinators such as honeybees that may be in your fields. WSU Extension Fact Sheet FS174E “Pollination and Protecting Bees and Other Pollinators” goes into depth about this topic.

Additional Information

EPA Releases Residual Time to 25% Bee Mortality (RT25) Data Reducing Pesticide Hazards for Bees

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