What is an economic threshold?

The economic threshold is the pest density at which the cost of control equals the value of the crop damage it would otherwise cause. Treating at or above this level is economically justified; treating below it usually costs more than it saves.

Where do these thresholds come from?

They are widely published integrated pest management thresholds from US land-grant extension programs. The classic soybean aphid threshold of 250 aphids per plant on actively growing plants is a well-known example used across the North Central states.

Does meeting the threshold mean I must spray today?

Not necessarily. Most thresholds assume the population is still increasing and the crop is at a susceptible stage. Check plant stage, beneficial insects, and weather, and rescout in a few days when you are near but below the threshold.

Why are some thresholds per sweep or per trap instead of per plant?

Different pests are sampled differently. Mobile foliage feeders are often counted with a sweep net, soil pests like rootworm beetles are monitored with sticky traps, and plant-bound pests are counted directly per plant. The unit shown matches standard scouting for that pest.

Should I always defer to local guidance?

Yes. Thresholds vary with region, crop price, control cost, and crop stage. Use this tool for a quick reference, then confirm with your state extension or a certified crop advisor before treating.

Pest Economic Threshold Reference Tool

Spraying below the economic threshold wastes money and beneficial insects; spraying too late lets a pest cause yield loss. This tool puts the standard integrated pest management (IPM) thresholds for major field-crop pests in one place and compares them to your scouting count so the spray-or-wait decision is clear.

How it works

Each pest has a published economic threshold expressed in its standard scouting unit. The rule is simply:

if scouted density >= economic threshold  -> treatment justified
else                                       -> continue scouting / no treatment

The economic threshold sits slightly below the economic injury level so there is time to act before damage becomes unprofitable. The tool reports your count, the threshold, and the percentage of threshold you have reached.

Example and notes

A soybean field scouted at an average of 300 aphids per plant on growing, pre-R5 plants exceeds the classic 250-per-plant threshold, so treatment is justified. A count of 150 is only 60 percent of threshold, so the recommendation is to rescout in a few days. Thresholds assume increasing populations and a susceptible crop stage — always confirm crop stage, beneficial-insect pressure, and current control costs with local extension before treating.