Answer: The Japanese beetles will defoliate plants in a bad season and this can stress the plant. They are difficult to control, especially with grape which is a beetle favorite. You could try to repel them using a neem-based spray. Milky spore or beneficial nematodes can be used to reduce the grub population in the soil, however this will not be effective unless a wide area is treated because the beetles are able to fly so far. The beetles can also be sprayed with carbaryl (Sevin) but this will only kill the beetles it contacts directly. Handpicking can also help, although it is time intensive. Do not use the pheromone traps as these lure more beetles to the area.
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