Locally, we’ve seen Japanese beetle adults over the past weekend, the 2nd of June. We continue to be amazed at the early emergence, usually 2-3 weeks ahead of schedule, of insects this year…the Japanese beetle being no exception. Many areas in the state are now likely seeing this notorious pest in crops and around the home.
This year’s adults are the result of eggs that were laid by female beetles last summer. After these eggs hatched, the grubs immediately begin to feed on a wide variety of roots and decaying organic matter in the soil. This feeding is typically not noticed and not economic. They continue feeding until cold temperatures prompt them to move deeper in the soil profile to overwinter. Early in spring, the surviving grubs return to near the soil surface to feed, and this is when they cause the most problems in field crops, turfgrass and other crops. Fortunately, we have heard of no Japanese beetle grub problems in field crops this year.
Japanese beetles are generalists both as adults and larvae and will feed on more than 350 different species of plants. As adults they are especially fond of roses, grapes, smartweed, soybeans, corn silks, flowers of all kinds, and overripe fruit. Beetle damage to cultivated crops is often minimal and defoliation (leaf removal) on soybean typically looks much worse than it is, and is often most severe along borders, where “drive-by scouting” tends to occur. The beetles often congregate in several areas of a soybean field, feeding on and mating in the upper canopy. The beetles’ iridescent, metallic color also frequently catches the attention of those doing “windshield” field inspections.
Closer inspection will often reveal that weeds (e.g. smartweed) have made fields even more attractive to the beetles. It has been years since we heard of treatable levels of adults in corn or soybeans, but stay vigilant. The mild winter certainly did not hurt their chances of survival at all. Happy Scouting!