I saw my first Japanese beetle adult (Figure 1; JB) today at a collaborating vineyard where we are looking at the interaction of social wasps and grape cluster rot pathogens. We have not yet seen any JBs at the West Madison Agricultural Research Station but this will be a matter of days before we do. Emergence usually begins right around Father’s day and they seem off to a slow start possibly due to the dry and hot conditions. It is recommended for grape, berry, and apple growers to start scouting for JBs throughout the state as they are now present as far north as Bayfield county.

Grape is a highly preferred host plant for JBs who feed voraciously on the leaves, causing skeletonization of the leaves. Grape plants are known to tolerate quite a bit of defoliation, as evidenced by all the thinning that is required each year, and 30% defoliation could be used as a threshold for implementing an insecticide application. Berry crops can also see feeding from JBs and may warrant an insecticide application. Apple trees can tolerate some injury from JBs as most feeding usually occurs on the leaves, though some apple cultivars, such as Honeycrisp, Lodi, and Pristine, have been reported to incur fruit feeding as well. Fruit injury may not have been caused by JBs and they could just be coming to feed on previously-damaged fruit. It is likely that apple trees can tolerate 20-30% defoliation without any impact on tree health and it is unlikely we would reach this high level of defoliation on apple trees in Wisconsin. It remains important to monitor young trees and high density orchards with small leaf canopies and to protect them in case of high JBs densities.

Several products can control JB adults, including organophosphates (e.g., Imidan), carbamates (e.g., Sevin), pyrethroids (e.g., Danitol, Baythroid, Mustang Maxx), and neonicotinoids (e.g., Assail). Organically-approved insecticides that have shown at least some activity against JB include Neemix, Azadirect, Surround, the soil born bacterial insecticide BeetleGone!, and Pyganic. Please read and follow the labels and check that the crop you intend to spray is registered on the label. As a preventative measure, soil applications of a neonicotinoid insecticide such as imidacloprid, clothianidin, or thiamethoxan in late June can help reduce future populations of JB adults on your crops. However, keep in mind that this strategy has been shown to be short-lived in blueberry as new adults from outside of the fields continue to move in.

For more in depth information on the biology and management of Japanese beetle, please visit our You Tube channel and watch the webinar on “What to do now in the vineyard: post bloom”.

Happy growing season!

This article was posted in Grapes, Insects and tagged Christelle Guédot, Grapes, insects, Japanese beetle, Japanese Beetles.