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 insect populations will flourish in population and cause crop injury. As the 2021 soybean crop enters R3-R4 and R5-R6, be on the look out 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.
- There’s another population that lives and feeds in the above ground canopy called ‘beneficial insects,’ which don’t harm the crop.
- Green Lacewing: feeds on aphids, eggs, leafhoppers, spider mites, etc.
- Lady Beetle: feeds 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 of these popluations 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?
a. What is the percentage of defoliation?
i. 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.
b. Where is the damage?
i. Not all insects feed on the same parts (foliage feeding vs. pod feeding).
c. When is the damage?
i. The timing of feeding can have a major impact and will influence economic damage or the need for a control treatment.
1. Feeding on pods and leaves during grain fill will be more impactful than leaf feeding during R1.
d. Who is doing the damage?
i. 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.
1. Piercing/Sucking: Stink Bugs
2. Chewing: Bean Leaf Beetles, Grasshoppers
e. Insect growth stage:
i. 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).
1. Complete: Egg, Larva, Pupa, Adult
2. Incomplete: Egg, Nymph, Adult
It’s easy to jump to the conclusion to spray an insecticide when a producer sees feeding in a soybean field, but as good stewards of the land, we must make these decisions with complete consideration.
1. If a field is sprayed with an insecticide, benefical 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 poplation emerge or migrate in?
4. Is this crop feeding a true risk to profit or is it more cosmetic?