I see some leaf damage from insects on small beans almost every year. I figure it is bean leaf beetle. My yields have been great. Is it worth worrying about that early season damage? Is there really any reason to scout soybeans that early in the season?
The Indiana Certified Crop Adviser panel includes Gene Flaningam, Flaningam Ag Consulting, Vincennes; Greg Kneubuhler, G & K Concepts, Inc., Harlan; and Bryan Overstreet, Purdue University Extension ag educator, Jasper County.
Flaningam: Soybean fields need to be monitored for early season feeding. Look at feeding damage to the cotyledons and unifoliate leaves on the soybeans. Excessive feeding can cause stand reduction, and possibly allow seedling disease to enter the plants. If bean leaf beetle have been a problem on your farm, look at seed treatment options. Rescue applications can be made with labeled post-applied insecticides if conditions warrant an application.
Kneubuhler: Most generally, early feeding on cotyledons or first or second trifoliate soybeans is from bean leaf beetle. Most insecticide seed treatments are very effective on them. However, if you don’t have seed treatments, you may see some feeding. It takes a significant amount of defoliation that early in the season to warrant spraying. To justify an insecticide treatment, you need to have 40% to 50% defoliation. That level of defoliation looks very bad. Although I have seen it, it’s quite rare to get that level of feeding that early in the soybean’s growing season. Scouting soybeans that early in the season for insects isn’t typically necessary. However, scouting that early for stand counts and herbicide performance will pay dividends.
Overstreet: Generally, that time of the year the damage you describe is from bean leaf beetle. However, Mexican bean beetle can also cause damage early in the season. The threshold of treatment for either of these pests is 40% defoliation in the vegetative stages. I would still scout soybeans but remember that it will take quite a bit of damage by these pests to consider treatment. The thing to remember is that while scouting you will also be looking for weeds, nutrient deficiencies and other issues while you are in the field.