Will grape plants come back in the spring after being infested with Japanese Beetles this season?
I planted four Frontenac grape plants last fall that appear to be doing well. Unfortunately the Japanese beetles got out of hand on them recently. I’m willing to chalk this year’s crop up for a loss; however, is it a foregone conclusion that the plants are now unviable moving forward or can I expect them to come back in the spring?
I’m sorry to hear about your Japanese beetle issues–my own blackberries are infested at the moment, as well, as they are most years! The good news is that the damage is largely cosmetic, as long as the plant does not become overwhelmingly defoliated. There can be some loss of the fruit crop, but I don’t anticipate healthy plants having trouble bouncing back next season.
That said, because you’ve just planted these vines, I would do what you can to remove the beetles, as young plants are more susceptible to problems because they haven’t yet fully established. The easiest and least toxic method is simply to knock them off the leaves into a bucket of soapy water every day or two while the population persists. If they tend to fall into grass below and disappear (they let go pretty easily when bothered), or if you don’t relish handling dozens of beetles, you can spread a tarp out under the vines and gently work the foliage with a soft broom.
I’ll include some Extension resources on management of Japanese beetles and their life cycle. They are an annual nuisance for many plants and the best way to mitigate the problem other than mechanical removal from the leaves is to address their grubs overwintering in nearby lawn.
Additionally, while there isn’t a great deal of research at the moment specific to Japanese beetles on grapes, I did find a study from Virginia Tech and one from UWisconsin that should give you some reassurance.