July is the best time to treat for European chafer grubs on home lawns

If you haven’t taken steps to deter grubs and your lawn has suffered from grub damage in the past, now is the time to apply an insecticide.

Nearly all of the grub damage to home lawns in Michigan is caused by the European chafer. It has now spread northward from southern Michigan to Saginaw, Midland, Muskegon and isolated locations further north like Traverse City, Alpena, and even into a few places in the Upper Peninsula, like St. Ignace and Marquette. Daily irrigated turf is rarely injured by European chafer, but home lawns, golf course roughs, roadsides or any low-maintenance site that tends to be dry during the summer is susceptible. Recent research has shown that turf with a large root system is much more tolerant of grub feeding than turf with a small root system. Take a look at the following figure from Dr. James Beard’s book, Turfgrass Science and Culture.

Figure from Turfgrass Science and Culture 

Notice how much larger the mass of turf roots is for the non-clipped turf compared with turf mowed at 1.5 inches. If homeowners raise the mowing height to the highest setting on their lawnmower (usually about 3.5 inches) and irrigate during dry periods, they are not likely to see grub damage.

Meanwhile, for those that suffered grub damage in the past and don’t want to have more problems this fall or next spring, the month of July is the best time to apply an insecticide for grubs. Choose a product for grubs that contains imidacloprid, clothianidin, acelepryn, thiamethoxam or halofenazide. For a complete list of effective grub control products for homeowners, including active ingredients, go to the MSU Turfgrass Science website and look at the grub control bulletin by Terry Davis (fourth bulletin listed on the cover page of the website).

Please note. The new GrubEx product now contains acelepryn as the active ingredient. Because of its low water solubility, acelepryn may require four to six weeks to become fully available in high organic soils or to penetrate lawns with thatch. For this reason, it is best to apply the new GrubEx before July 15 (May 15 to July 15 is optimal). For products containing the other active ingredients listed above, any time in the month of July is excellent timing.

Reference article: Understanding lawn grub control products

Dr. Smitley's work is funded in part by MSU's AgBioResearch.

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