Research Highlights

Research Highlights
Considerations for Insecticide Use

Photo: United Soybean Board

By Todd Steinacher

For many in the agriculture industry, a soybean field is an amazing population of plants that convert sunlight energy and nutrients into a high-volume output of oil and proteins. However, to insect populations, a soybean field is an amazing buffet! Regardless of what we plant and when we plant it, Mother Nature will always send a critter to feed on it. If food sources are good, many insects will flourish in population and cause crop injury. 

As the soybean crop enters R3-R4 and R5-R6, be on the lookout for bean leaf beetles and stink bugs because both of these insects can cause a grain impact of quantity and quality. The decision to apply an in-crop insecticide should not be taken lightly and should be evaluated to the fullest.

In a soybean field, there are numerous biological populations living and thriving. Many of these populations live and thrive below the ground and provide value to the soil and growing crop such as fungi and bacteria.

There’s another population that lives and feeds in the above-ground canopy called ‘beneficial insects,’ which don’t harm the crop. These include the green lacewing, which feeds on aphids, eggs, leafhoppers, spider mites, etc., and the lady beetle, feeding on aphids, eggs, spider mites, etc.

The remaining populations are there to feed and reproduce. Some of these populations cause crop damage, but don’t impact yield or economics. Others can and will cause yield and economic impacts and these populations need to be identified, monitored, and responded to if needed.

How to evaluate damage

There are several questions to ask in scouting for insect damage. 

What is the percentage of defoliation? In many situations, foliar feeding insects seem to have a major impact based on the amount of feeding taking place. However, to actually cause an economic impact, there needs to be significant defoliation not only across the plant but across a given area of a field. 

Where is the damage? Not all insects feed on the same parts (foliage feeding vs. pod feeding).

When is the damage? The timing of feeding can have a major impact and will influence economic damage or the need for a control treatment. Feeding on pods and leaves during grain fill will be more impactful than leaf feeding during R1.

Who is doing the damage? Not all insects feed the same way. When you see the pest, observe how it feeds on the plant, and when you see similar feeding damage, you will then know which insect caused it. This information will be helpful when making decisions for treatment. For example: stink bugs eat plants by piercing/sucking; bean leaf beetles and grasshoppers are chewing insects.

Also consider insect growth stage. All insects go through very structured growth stages or life cycles. Knowing this information will help to understand the amount of crop injury to expect and if the insect is at the start of its major feeding or towards the end of the major feeding (treatment or no treatment).

Considerations before spraying

It’s easy to jump to the conclusion to spray an insecticide when you see feeding in a soybean field, but as good stewards of the land, the decision to spray must come with complete consideration. 

  1. If a field is sprayed with an insecticide, beneficial insect populations will also be damaged. Is the reduction in beneficial insects worth the reduction in the primary feeding insect?
  2. Is the insect feeding during a major growth stage and will it impact yield?
  3. If the insect is sprayed for, could another population emerge or migrate in?
  4. Is this crop feeding a true risk to profit or is it more cosmetic?

Answering these questions before spraying an insecticide can reduce unnecessary costs and chemicals on the land.

Todd Steinacher is an ISA CCA Soy Envoy alum and currently supports ISA on agronomic content as well as serving as an Illinois CCA board member. He was recently awarded the 2020 IL CCA of the Year & the 2021 International CCA of the Year. He has over 15 years agronomic experience, currently working with AgriGold and GROWMARK previously. Steinacher has an associate degree from Lincoln Land Community College, a B.S. in agronomy and business from Western Illinois University and a master’s degree in crop science from the University of Illinois at Urbana-Champaign. He can be reached at

Reprinted with permission from ILSoyAdvisor.

Published: Aug 22, 2022