Raise your mower height to 3.5 inches to help grass withstand grub damage

Mowing turf to 3.5 inches will help it develop a larger root mass that can recover from grub damage with less pesticide use.

Since the 1990s, the European chafer (an introduced beetle) has damaged many lawns across the southern half of Michigan’s Lower Peninsula. Currently, the European chafer has spread northward to Saginaw, Midland and Muskegon and has been found in isolated spots in Traverse City, Alpena and a few sites in the Upper Peninsula. European chafers, along with Japanese beetles, another imported insect, feed on the roots of grass while in their grub stage, making it difficult for the plants uptake of water. Grub damage has become so common that control of the insect has become a yearly routine on many golf courses and home lawns.

A recent article from Dave Smitley, MSU professor and MSU Extension specialist, reported that approximately $20 million is spent on lawn insecticides in Michigan and that it is mostly used to avoid grub damage to the turf. The C-shaped white grubs causing the damage are the immature stage of European chafers and Japanese beetles. Often, the first sign of damage is browning turf caused by grubs feeding on grass roots in the fall and early spring. Insecticide treatments can help to minimize grub damage, but use of insecticides may not be necessary if the proper cultural practices are followed.

We have known for awhile that watering practices can reduce the impact of the grubs. Studies show that turf irrigated daily in mid- to late summer can tolerate higher populations of grubs before damage occurs. Now scientists are looking to other lawn cultural practices to help reduce the use of pesticides in the battle against grubs. New research shows that raising the mowing height results in a large increase in root mass. A larger root system lessens the chance of damage by grubs that feed on these roots. Smitley states, “Research at MSU indicates that if turf root systems are dense enough, it is unlikely that grubs will consume greater than 60 percent of the root mass, which will leave enough roots for your lawn to survive without seeing any dead patches.” Setting your mower to a height of 3.5 inches above the ground will help the turf develop this larger root mass.

The combination of turf growing at 3.5 inches along with watering lawns during dry periods makes it unlikely that grubs will damage the lawn. “Cut it high” is more than a slogan; a higher mowing height helps crowd out weeds, promotes deeper roots and helps the lawn withstand drought conditions. Now another benefit can be added: it prevents grub damage without the need for insecticides.

Raise that mowing height even in the fall. Michigan turf grasses, like Kentucky bluegrass, grow best during cool, moist weather. Cool conditions in fall are perfect for improving the health of your lawn and one simple practice to benefit the lawn is to raise the mowing height to 3.5 inches.

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