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Getting rid of Japanese beetles

Friday - 6/3/2011, 12:29pm  ET

Beat the Beetles

WTOP Garden Editor Mike McGrath

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Worried about Japanese beetles? Put up a birdbath

Sharon in Columbia, Md. writes: "What do you recommend to avoid Japanese beetle problems? Is this year expected to be a bad one?" Well, Japanese beetle infestations seem to be cyclical and localized, Sharon. I haven't seen any the last two years, while others have reported heavy ravishing of their roses. Ah, but perhaps one reason for my un-ravaged roses is that we provide a great year-round habitat for birds. We use no dangerous pesticides, feed the birds heavily with suet in the winter and provide lots of fresh water in the summer-all tactics that will bring lots of winged pest eaters flocking to your plants as well.

Note: if you want this to work for you, don't feed birds anything in the summer; let them find natural food-like beetle grubs and armored adults. The only thing they need from you is clean, fresh water-which gets scarce in the summer.

Be ready to catch that first beetle of the season

Sharon in Columbia, Md. wants to know how to deter Japanese beetles. One great way is to use a beetle trap as a monitoring station. Buy one of those Japanese beetle 'bag traps' with a lure, set it up near your most commonly attacked plants and check it every day. When you see your very first beetle inside, take it down, wrap it in plastic and store it for the same use next year.

Then cut any roses that are blooming or fully formed and bring them inside to display in vases. This will stimulate the plants to produce a new flush of blooms very quickly.

Then cover the rose bushes and any other plants the beetles typically love to attack with sheer curtains or row covers. Or spray the plants heavily with a feeding deterrent like neem or garlic oil (typically sold as an all-natural backyard mosquito fogger). Keep the covers on or keep spraying for the next two weeks.

Studies show that if you prevent that initial feeding frenzy, the beetles will move on to easier prey, and few-if any-will return when you stop spraying or remove the protection.

When beetles appear, be ready

  • Do use a single trap to monitor for their emergence, but don't use Japanese beetle traps as protection for your plants. Their powerful lures attract so many beetles that the numbers reaching-and eating-your plants are typically doubled.

  • Don't use chemical fertilizers like Miracle-Gro, Osmocote or the dreaded '10-10-10.' The lush weak growth they cause attracts pest insects like mad. Feed your plants with compost or a gentle balanced organic fertilizer.

  • Hand pick beetles in the morning when they're sluggish, and drop them into a bucket with a little soapy water in the bottom.

  • Have an organic pesticide containing neem or spinosad ready. These are two of the safest (for you and the environment) and most effective (as deadly to insect pests as chemical insecticides) things you can spray on pests such Japanese beetles.

Don't let your lawn become a Japanese beetle nursery

Now it's time to discuss prevention. After ravaging your roses, female beetles mate and then look for a place to lay their eggs, specifically they're searching for a soaking wet lawn that's been scalped or has bare spots. Female beetles will not lay eggs in dry soil or try and fight their way through a correct 3-inch cut.

So, in addition to keeping your grass green during the height of summer, a 3-inch cut, deep, weekly waterings and no summer feedings will prevent beetle grubs from eating the roots of your turf this fall. There's just no end to the good things that can happen when you finally start to care for your lawn correctly.

If despite your best efforts (or more likely because you made no such efforts), you wind up being attacked by massive numbers of beetles this summer, treat your lawn in late summer with Milky Spore disease, a naturally-occurring soil organism that's deadly to beetle grubs (and only to beetle grubs) and available at most large independent garden centers.

NOTE: You must apply it in late summer. Milky spore that's spread in the spring won't do a thing. (In fact, I wish garden centers would stop selling it in the spring. It's a waste of time and money then, and gives gardeners a false sense of protection.)

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