Ask Wine Wizard

Japanese Beetles

TroubleShooting

Edwin Kaarela — Westminster, Massachusetts asks,
Q

Early this year my Frontenac vineyard at my daughter’s in Waldoboro, Maine became covered with thousands of Japanese beetles, which seemed to eliminate the entire leaf structure. It appears there is no way to eliminate these beetles, unless you have the answer? Incidentally, the grapes seemed to survive somewhat, yet they tasted sour.

A
Wow, that’s quite something! Though you seem to have been able to identify the insects on sight, your picture definitely shows the tell-tale “lacy” cutout pattern on the leaves that are the hallmark of the voracious “Japanese Beetle” (Popilia japonica). These little half-inch long bugs tend to be present in the Midwest and eastern United States and like to feast on roses, hops, and, as you well know, grapevines. Like just about all vineyard pests, there really is no way to eliminate them entirely but they can be “managed,” especially in the long-term. First of all, Japanese beetle traps seem to have limited functionality as the pheromone bait, in various studies, was shown to actually attract more beetles then they trapped. Since they are slow-moving and are especially inactive on cold mornings, small infestations can be managed by hand picking them off and discarding them into a bucket of soapy water. Larger areas affected by many of them can be treated with pyrethrin sprays, which are natural, biodegradable insecticides and repellants derived from plants. Insecticidal soap and kaolin sprays have
Response by Alison Crowe.