Japanese beetles are monitored using pheromone-baited traps as part of the MU IPM Pest Monitoring Network. Last week, Japanese beetles started to show up in trap captures in several counties in southwest, east central and southeast Missouri (SEMO counties = Ste. Genevieve, Mississippi and Oregon Counties). Japanese beetles are pests of ornamentals, grapes, turf, corn and soybeans. Japanese beetles have been in Missouri for several years and have been progressively marching south. Recent observations suggest that the first couple of years you may catch a couple of beetles and at some point afterwards, captures may be in the thousands a night. In 2010, Mississippi County captured 12,000 over a 3 day capture period and Stoddard County captured 108 over a 3 day capture period. Beetles begin to emerge around mid-June and will be out through late July – early August (see the graphs below for historical data for population spikes and the duration of beetle captures for several SEMO counties).
Typically, when Japanese beetles first move into an area, they are problematic on ornamentals. Once they become established, they move to crops. In Missouri, the Wine Industry is battling with this insect and last year there were a couple of reports of soybean and corn fields that were treated for Japanese beetles in Mississippi County.
In corn, Japanese beetles tend to concentrate on field margins and a spot treatment may take care of the problem. This year we are going to look at thresholds in corn more closely, but current recommendations for treatment are 3 or more beetles are present on green silks, silks are eaten to ½ or less in length and pollination is less than 50% complete. In soybeans, threshold are based on defoliation: 30% defoliation for vegetative beans and 20% for reproductive beans (flowers and/or pods present). Check out the Pest Management Guide for recommended products if you need to make a treatment.