They may be unseen, but underground grubs are a hidden threat to your landscape. June bugs and Japanese beetles are just two of the several types of beetles that may lay eggs in your lawn. These eggs hatch in the late spring or early summer, and the resulting grubs attack your lawn's roots and create widespread yellowing, wilting or brown spots. Treat your lawn with insecticides to immediately eradicate these pests.
Mow your lawn to the lowest height that's acceptable for your specific lawn species. This will allow your grub treatment products to effectively penetrate the lawn. Acceptable heights vary by grass type. For example, hybrid Bermuda grass can handle a height of 3/4 inches, while red fescue should be kept at 2 1/4 inches. The University of California/Davis has full recommendations on mowing heights for some of North America's most popular lawn species. Find a link in Resources.
Treat the lawn if you count 10 or more beetle grubs in a square foot of grass. Check by using a spade to lift up the sod. Any fewer than 10 per square foot, and your lawn does not yet need a treatment.
Treat your lawn. Spray the grass with a permethrin- or acephate-based lawn insecticide. This kills the grubs upon contact. Follow the insecticide's label for application instructions, as potency varies widely by brand and product.