It is a unique concern when aphid populations near or reach an average of 250 aphids per plant when the plant is beginning to full seed, said Dr. Ron Hammond, OSU Extension entomologist. This is because, as of yet, researchers have not been able to establish an economic injury level, or the amount of injury which will justify the cost of an insecticide.
It is believed that higher EILs will need to be reached during the full-seed stages — up to 700 to 800 aphids per plant — before a rescue treatment is warranted. Also, entomologists assume that plants in the late stages are probably not as succulent to insects as plants at a younger growth stage. Thus, it is inconclusive for aphid population to go much higher at this time.
Hammond suggests that prior to making any decision to spray, that growers sample multiple times over a number of days to make sure that the level is indeed rising well more than the current threshold of an average of 250 aphids per plant.
Second-generation bean leaf beetles are emerging and feeding on soybean pods. Pod injury is a problem because of yield loss and seed quality issues. This concern is especially important with food grade soybeans and soybeans being grown for seed. If bean leaf beetle populations are high and actively feeding, with plant injury at 10 percent or greater, an insecticide may be warranted to prevent further pod injury. Pod injury also vectors disease and fungal infection into the soybean seed.
Remember, any time you must use a late-season insecticide, please consider the preharvest interval, which is the time period you must wait prior to harvest, after an insecticide has been applied.
For more information and pictures on these issues, please see my blog under “Clark County Agronomic Crop Update,” dated Aug. 30: http://westohcropweather.blogspot.com.
Jonah T. Johnson is the extension educator for agriculture at the Ohio State University extension office in Clark County.
About the Author