Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu
Scout soybeans for early season pests including grasshoppers, bean leaf beetles, slugs, and deer.
Continue to sample fields for slugs and other defoliators. The past few weeks, I have seen several fields with grasshopper and bean leaf beetle feeding injury. Soybeans can typically withstand a decent amount of defoliation before yield losses occur, however, if stands are being reduced, an insecticide application may be warranted.
A treatment may also be needed if you are finding one grasshopper per sweep and greater than 30% defoliation. (Note: once plants reach bloom and pod fill stages, the threshold for defoliation is reduced to 15%).
Here is a short Youtube Video discussing early season soybean pests: https://youtu.be/ug6wHwIHftk
Grasshopper feeding injury on seedling soybeans. Notice the irregular shaped holes and leaf feeding from the leaf margins, a good indication of grasshopper feeding.
In addition to grasshoppers, also keep an eye out for bean leaf beetle damage (chewing on cotyledons and small round holes in unifoliate and trifoliate leaves). This can often be confused with slug damage so look for slime trails, slugs, and beetles. The threshold for bean leaf beetles is 2 per ft of row and 25% stand reduction from emergence to 2 trifoliate. After 2 trifoliate, the threshold is 2-3 per plant and 30 percent defoliation.
Bean leaf beetle feeding injury. Bean leaf beetles will often drop from the plants when disturbed and are excellent at hiding under crop residue.
Slug injury on soybean unifoliate leaves. In some cases, this damage can look similar to damage from bean leaf beetles so when diagnosing the cause, be sure to look for slugs, slug slime trails, and for beetles.
Here is a link to our Soybean Insect Management Recommendations: https://cdn.extension.udel.edu/wp-content/uploads/2012/05/18063934/Insect-Control-in-Soybeans-2017-final.pdf
I also had several calls this week about deer damage and have heard of many other fields with stand losses from deer. Here is a picture of soybeans with deer damage.
Deer damage to soybeans