Grubs can be doing serious damage to your lawn at this time of year and you may be unaware what is happening.

Those Japanese beetles and several other types of beetles started the damage last summer. Right now is the time to prevent them from doing further damage. In fact, the ideal time to make Butler County lawns grub-proof is July to mid August.

White grubs are the immature stage of several beetles that inhabit our area. These include masked chafer, Oriental beetle and Japanese beetle. The beetles are mainly active between June and mid August. They lay eggs 1 to 2 inches deep in moist soil of lawns. The young hatch in about two weeks and begin feeding on grass roots.

The grubs grow quickly and become nearly full size by autumn. At first frost, the grubs move deeper in the soil for hibernation. They return to the root zone and resume feeding in early spring. In May or early June they transform into pupae and a few weeks later emerge as adult beetles.

Damage from beetles is usually most severe in late summer when they are vigorously feeding and the grass may be under stress from drought. Without roots to extract water and anchor the turf, the grass dies and sod easily lifts from the soil. Skunks, raccoons, crows and other varmints may dig in the turf to feast on the juicy grubs. Lawn damage is usually less apparent during the spring feeding period.

Diazinon, Dylox, and Oftanol have been the most common insecticides used to kill grubs. All of these have short residual toxicity, usually not more than two weeks. This requires that they be applied in a relatively narrow window of opportunity to be effective. If you apply them too early, the insecticide may degrade before the eggs hatch. If you make a late application, severe damage may already have occurred.

In our area, the ideal time for applying these three insecticides is late July to late August. Optimum timing can vary by a couple of weeks, depending on the type of grubs.

Two new insecticides for grub control have been recently introduced to the retail market. The trade names for these products are Merit and Mach 2. Both can be applied up to two months before the grubs hatch. Both exhibit low toxicity to humans and pose relatively little hazard to the environment.

Merit belongs to a new class of synthetic insecticides that act on the insects' nervous systems. It kills grubs by both contact and ingestion. It is highly effective against young, newly hatched grubs, but is not effective against large grubs. Merit can be purchased locally as Bayer Season Long Grub Control or Scott's Grubex.

Mach 2 is a new type of insecticide called insect growth regulator. When even a tiny amount of the substance is ingested, the grub immediately stops eating and begins to die. Unlike Merit, Mach 2 will control large grubs. Although large grubs stop feeding immediately, they may not die and decompose for several weeks. This may not be quick enough to discourage skunks and raccoons from digging. Mach 2 can be purchased as Ortho Grub-B-Gon.

It is essential when applying any grub insecticide to thoroughly irrigate after application. The insecticide must be flushed through the thatch and the grass roots to be available for the grubs to ingest. Irrigation should be done immediately after applying Diazinon, Dylox or Oftanol, because these products are only toxic to the grubs for about two weeks after application.

Merit and Mach 2 are effective for two to three months and normal rainfall will water them into the soil.

Pete Hale of Sarver is a Master Gardener with the Penn State Master Gardener program.