Integrated Pest Management (IPM) is a science-based approach that combines several techniques to control insect pests before they can cause significant damage to the crops. As part of an IPM program, soybean farmers should scout fields regularly and only treat fields when insect pest populations reach economic threshold levels (profit-threatening). This approach is important to maintaining maximum yields and profitability.

Scouting

Scouting is a field survey designed to determine pest population levels or their damage. Understanding insect activity throughout the growing season is important for making in-season integrated pest management decisions and planning future actions. Several techniques can be used to evaluate insect presence in a field, including visual counts, using a beat cloth or sweep net, and looking for injured plants.

Figure 1 Use of a beat sheet (A) and a sweep net (B) to estimate insect pest populations in soybeans. Photo courtesy: Lennis A. Rodrigues

General scouting guidelines:

• In general, scouting should be performed at least weekly.
• Break large fields into units of 40 to 50 acres considering similar field characteristics (e.g., soil type, past pest incidence, previous crop).
• Walk in a pattern to assess the whole field broadly (e.g., U, X, or a W pattern). Avoid picking out good or bad spots.
• Start sampling at a different location in the field every time you scout.
• Avoid sampling only at field edges as many insects migrate from surrounding areas into the fields. If a problem is found, try to determine whether it is isolated or widespread.
• When estimating the percentage of defoliation consider the entire canopy.

Insect identification

Insect identification is also a key component of an IPM program. Proper insect identification and the injury associated with pest species are critical to determining the best management strategy.

Figure 2 Example of wind/rain/hail damage (A). Photo courtesy: Micah Doubledee, University of Missouri, Field Specialist. Bean leaf beetle feeding injury (B).

Insecticide application

Insecticide application is only recommended when thresholds are exceeded. These thresholds are based on the number of insects found and/or the damage caused by them. For example, soybean defoliation threshold levels vary according to the soybean growth stages. From V1 to R2 growth stage, the threshold is 30%, while R3-R5 is 10% of defoliation. Following threshold levels prevents unnecessary insecticide use, delays insecticide resistance evolution, and favors the build-up of natural enemies.