The Q&A Archives: Japanese Beetles

Question: My red raspberry patch is mulched with leaves and grass clippings. During picking season I can kill by hand about 50 Japanese beetles every night. Do they lay eggs and hatch in the earth of my berry patch? It is about 15 by 25 feet. I used a bag style catcher with the pheromone bait and changed the bags daily due to hundreds being caught every day. Am I attacting bugs from beyond my yard that normally wouldn't have come by using the trap? If they hatch in the dirt where the bushes are, can I do a pre-emptive strike by spraying the soil with a chemical to kill the larvae? They absolutely decimate the greenery on the bushes!

Answer: It's possible you're attracting additional Japanese beetles with your pheromone trap, but it's also possible they'd find the leaves of your plants with or without the pheromones. There's a product called 'Milky Spore' you can try using to eliminate the grubs in the soil. Milky Spore is a naturally occuring microscopic bacteria (Bacillus popillae), that kills grubs before they can turn into adults. It's best used when the soil is warm, so you'll need to wait until this spring to treat the soil. In the meantime, remove the old mulch material from the bed, scatch the soil up a bit to expose any eggs or larvae to the weather and to predators, leave it for a week or ten days, then mulch the bed with new organic material. By disposing of the old mulch, you'll probably be removing a whole generation of Japanese beetle eggs and grubs. If you use a floating row cover (or other spun fabric) on top of the soil before putting down new mulch, you'll also keep any remaining grubs from hatching into adults and invading your raspberry patch. If you still have problems next spring, remove the pheromone traps and use the Milky Spore bacteria.

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