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Knowledge to Grow by Karen Weiland - White Grubs

Does your lawn show wilting and browning in irregularly shaped areas? If so you may have an infestation of white grubs. There could be many reasons for lawn browning, especially in late summer when rainfall is not abundant, but this is the time of year when most grub damage occurs. White grubs feed on the roots of grass. Check the root zone of affected areas by carefully pulling back a section of the sod and look for the white, c-shaped grubs, especially the area where brown grass meets green grass. Another tell-tale sign of grubs present is the visual damage from skunks and raccoons digging in the sod for grubs to feed on, which usually happens during the night.

Grubs do not usually appear in the shaded areas of lawns. The adult beetles prefer to lay their eggs in a well watered, sunny location. The masked chafer (white grub) and the Japanese beetle lay eggs in July. Your lawn will be a prime target for egg laying if the weather has been dry, your sunny lawn is irrigated and surrounded by non-irrigated lawns. One option to prevent damage is to allow the lawn to dry out and go dormant, if the weather allows. This will reduce the odds of grub damage since the adult beetles prefer moist soil to lay their eggs in. The downside is that you have to live with a brown lawn.

Masked chafers, which are the adult of the white grub, are tan beetles with six legs and are active shortly after sundown. Japanese beetles have six legs, a black head and bronze wings. They fly about during the day and feed heavily on ornamentals. Many factors may increase the chance of grubs infesting your lawn. A significant amount of beetles in your lawn in July is an indication you may have a grub problem later. Keep an eye on your lawn starting about mid-August into September. If you spot wilting and browning areas, check the root zone for grubs.

Imidacloprid (Merit), halofenozide (GrubX) and gamma-cyhalothrin (Spectracide) can be applied prior to damage for season long control. These should be watered into the soil for best results. Read and follow all label directions. Check the active ingredient section on the front of the label to confirm the products’ active ingredient.

As far as organic controls go, Heterorhabditis bacteriophora nematodes have shown good results. Nematodes are very small, unsegmented worms. After entering the grub, this particular specie will release a bacteria that will kill the grub. They are sold through mail order catalogs as Hb nematodes. Milky spore is another organic option. This bacteria will multiply over a number of years to control grub infestation.

As always, Happy Gardening!

The Purdue University Cooperative Extension service can be reached at 499-6334 in LaGrange County.