Fortunately, Japanese Beetle infestations are short-term. The adults emerge, mate and lay eggs and die over a relatively short period. Unfortunately, large numbers of beetles can seriously damage cultivated plants in that short period of time, and their grubs feed on the roots of grass and ther plants the rest of the year. Some suggestions for dealing with these pests:
Not much help for this year, but controlling grubs in the immediate area does reduce numbers in succeeding years. Chemical controls are best applied in late summer, after the current season's eggs have hatched and the grubs have begun to feed. There are numerous products available for eliminating grubs, the one you choose MUST be labeled for white grubs, and the package directions MUST be followed exactly. Your local Cooperative Extension Service can help determine the best time to apply in your area.
Biological controls include beneficial nematodes and Milky Spore disease, both of these attack only grubs, and prevent recurrence for years. See "Help! Grubs are killing my lawn!" in this section for more info on biological controls for grubs.
In areas with heavy beetle attacks year after year, choosing landscaping plants that Japanese beetles naturally avoid, or rather NOT choosing their favorites is a good idea. Again, your local Cooperative extension service can help with list of preferred/ avoided plants for your area.
You could also try interplanting with species that are known to actively repel the adults, white mums, rue, tansy, larkspur, garlic, citronella.
Garlic and citronella sprays are also said to help repel beetles.
Controlling adult beetles
Chemical controls: Diazinon and Sevin sprays will take down the adults. Be sure to follow the label directions EXACTLY and use care when spraying ANY poisons.
Rotenone and Pyrethrum sprays are also effective .While these are made from plant sources and more environmentally-friendly, they are still poisons and should also be used with care. Neem oil has also been suggested, though with varying success reported.
Whichever one you choose, the sprays must contact the insect to be effective.
Mechnical methods: The classic pick-and-squish-or-stomp method works, especially with small infestations on specific plants. Some gardeners knock the slow-flying insects into containers of soapy water, kerosene or oil. Vaccuum cleaners are also suggested, particularly the small " Dust-Buster" portable types.
Traps will attract large numbers of beetles...but the consensus is that they just bring more beetles to YOUR property, as the sexual/floral lures used in these traps travel great distances.
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