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When Are Rescue Treatments Against Japanese Beetles Recommended?

July 11, 2018

It is that time of year again when Japanese Beetles are emerging and are doing what they do best: eating everything in sight. Japanese Beetles, the ½ inch green and copper colored pest, eat everything from vegetables and row crops to weeds; their extremely wide host range makes them hard to miss during periods of increased activity, particularly along field edges. The increase in Japanese Beetle activity has led to questions from producers regarding thresholds for corn and soybean rescue treatments.

It is important to remember that pest populations along field edges are not always good indicators of what is happening in the rest of the field, so scouting location and technique is important. For corn and soybean, 10 plants should be observed in at least 5 places throughout the field to get an accurate representation of the field. Thresholds for rescue treatment in corn are determined by the number of beetles per plant or the amount of damage to the silks, while threshold for soybean are determined solely by percent defoliation.

According to the University of Illinois, damage thresholds for soybean rescue treatments include 35% defoliation before flower bloom and 25% defoliation after bloom. For corn, there are two thresholds that should be considered before a rescue treatment is applied: 3 or more beetles per ear or silks clipped to ½ inch. In corn, rescue treatments are not recommended when and pollination is more than 50% complete. Producers with questions are encouraged to contact Phillip Alberti, University of Illinois Extension Crop Science Educator, at 815-235-4125 or

Source: University of Illinois