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Plant Eating Beetles & Grimy Grubs
Question. Dear Mike: Every year, wehave an invasion of Japanese beetles; they destroy everything! I haveheard there is an oil that may work against them. Can I get it in astore or do I have to order it from a catalog? Sincerely,
            ---Jennie, onthe Eastern Shore of Virginia near the Maryland border
Mike: When I turned over the soil in one of my raised beds, I foundmore than a dozen grubs. Should I be concerned about my crops? Grubshave successfully devoured most of the lawns in my ruralneighborhood.                    
            ---JoAnn;Washington, NJ
Mike once described a homemade insect repellant for roses. I think ithad garlic in it. Anyway, it really worked, but I've lost the recipe.Can you help before the Japanese beetles arrive? Thanks, ---Jane inWilmington, Delaware

Answer. I wouldn't worry about grubsharming garden crops. These soil dwelling larval forms of a variety ofdifferent scarab beetles (Japanese, June, rose chafer, etc.) did mostof their eating last year—in the late summer and early fall. Right now,they're mostly just hanging out until they morph into their flyingdefoliator adult form.

If, however, you still wish to dispatch them—perhaps in the hope ofpreventing damage by adults this summer—beetle grub expert Dr. MichaelKlein, Adjunct Professor of Entomology at Ohio State University,suggests beneficialnematodes. Sold mail order by the multi-millions, they're packagedin little sponges or as water dispersible granules. Water them intomoist soil with a watering can or sprayer early in the evening (NEVERin the heat of the day!) and they should decimate the grub populationbelow within a few weeks—perhaps in time for those of you in the Northto prevent some of this year's beetles.
The always-popular "Spikes of Death" are a more immediate and certainoption. As I've often noted, those familiar 'lawn aerating sandals' aretotally useless for aerating lawns—you need to remove plugs of earth todo that. But they are perfect for dancing on your lawn to kill grubs,especially in late spring, when the big fat beetle babies are close tothe surface. Dr. Klein explains that you only have to nick a grub withthe spikes, and those spikes can nick a lot of grubs; studies haveshown a better knock down from Dirty Dancing than chemicalinsecticides.

The technique is so effective that New Zealand has approved 'spikingmachines' for the control of what they call "pasture/lawn grubs". Andthat's an important term. Once upon a time, you could be confident thatgrubs feasting on grass roots were Japanese beetle babies. But so manyother types of grubs have migrated into lawns, explains Dr. Klein, thatin some places, Japanese beetles only make up 25 % of the population."Grass death by grub", once only a Northeast worry, is now an equalopportunity scourge all across the country.

But again, as with purely Japanese beetles, the real damage to lawns isdone in late summer/early fall, when the grubs are at their biggest,hungriest stage and feeding heavily on grass roots. This is doubly hardon the cool-season grasses grown in the North, because those lawns arealready under lots of stress at that time of year from the summer heatthey so despise. Just as in the Spring, you can use nematodes or Spikesof Death to protect your turf…

…or you can avoid the problem by making your lawn less of a target thissummer. Dr. Klein explains that bad lawn habits—scalping and"compulsive overwatering"—are often to blame for grub damage. Cuttinggrass at the recommended height—on average, two inches down South andthree in the North—makes it more attractive to the eye, and lessattractive to egg laying females. And keeping it as dry as possible inlate summer will cause lots of beetle eggs and grubs to desiccate anddie.


You Bet Your Garden   Question of the Week  © 2006Mike McGrath