Potential Adult Damage
Photo of adult Japanese beetles feeding on soybeans. Photo credit: Laura Flandermeyer
Adult Japanese beetles are flying around corn and soybean fields! On corn, Japanese beetles decrease pollination through silk feeling. On soybeans, adults skeletonized leaves, harming the crop. If you have silking corn or are growing soybeans, it’s time to scout your fields, so this damage does not surprise you. Be aware that damage may be below economic threshold.
Critical Economic Information
For Corn: The economic threshold is 3 beetles per ear actively feeding . Moreover, silks must be <1/2 an inch long & pollination less than 50% complete.
For Soybeans: The economic threshold is 20% leaf defoliation for plants that have bloomed and 30% in those that have not.
Chemical control:
Refer to A3646, Pest Management in Wisconsin Crops, by following these links for Japanese beetle insecticide recommendations in corn (pg. 72) and soybeans (pg. 132).
Scouting
For corn, be sure to check 5 sets of 20 plants for feeding beetles. Note the tassel length, pollination progress, and number of beetles per ear.
For soybeans, scout 10 plants throughout the field. Look at those in the trifoliate stage and examine the upper, middle, and lower canopy on each plant, noting the extent of the damage.
Remember never use baited traps to scout!
Learn more with UW-Madison Extension’s Japanese beetle resource and DATCP’s Field Note’s section on Japanese beetles.
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