Japanese beetles - Knowledgebase Question

mt.prospect, Il
Question by sherimuc
March 22, 2010
I had Japanese beetles last year.I sprayed soap on them everyday and killed most of them,will they come back?If yes what can i do to prevent them? thanks

Answer from NGA
March 22, 2010


You didn't mention whether you have a grub problem in your lawn, but it seems likely if you had that many Japanese beetle adults last year. Japanese beetle grubs are best controlled by spraying beneficial nematodes on the lawn and garden area. These microscopic worm-like creatures attack only the grubs in the soil and not plants, animals or humans. Spray them in spring when the soil temperatures are above 55F and you should see a difference in summer. It's important to maintain soil moisture to keep the nematodes viable and so they can move easily through the soil. I suggest that you moisten soil well the day before you apply them, or wait until after it rains. Another product is milky spore powder, a naturally-occuring bacteria that kills grubs; you simply apply the powder in a grid pattern on your lawn. The powder is harmless to earthworms and other creatures. The bacteria will continue to multiply, and will keep working for up to 20 years. (The results won't be immediate, however; it will take some time to notice a decline in the grub population.) Finally, make sure your plants are healthy with appropriate water, soil and nutrients. That's the best way to keep pests at bay. Hope this info helps!

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