There are many defoliators in Midwestern soybean. Their feeding gets lumped together when estimating injury to determine the need to treat. Action thresholds in the region are similar among states: 30-40% in the vegetative stage, 15% at bloom, and then 20-30% up to R6 when spraying is not needed. These thresholds are good, developed in field trials in across many states, using both natural and artificial defoliation. The thresholds seem high, but remember the measurement is not of damage to pods or beans, but simply to leaf tissue which has some ability to replace itself. Also, spend some time under a typical soybean canopy – Its shady under there. While the top leaves capture full sunlight, the lower leaves aren’t working at full speed. They are extra capacity which can make up for defoliation at the top of the plant where insects like Japanese beetle, bean leaf beetle, and grasshoppers tend to feed.