A grub is in the beetle family Scarabaeidae. It is shaped like a "C" and is the thick-bodied stage of a growing beetle, called the larval stage. Grubs feed on organic matter, including the roots of your lawn. The species of beetle and its life cycle determine when grubs will hatch.
Control Is Difficult
Beetles fly and lay eggs, so don't expect to get 100 percent control of grubs. Too many grubs will kill the grass at the roots. Grubs do the most damage August through October, when they are feeding and growing. Damage to the grass will show up that fall and the following spring. The younger the grub is, the easier it will be to control. Fall treatments are ineffective because the grubs are too far down in the soil for chemicals to reach.
Chemical Prevention Treatment
There are chemical prevention treatments for grubs in your lawn. Prevention treatments are a relatively new class of synthetic insecticides that use either the active ingredient imidacloprid or halofenozide. Imidacloprid is a neuro-active insecticide that kills grubs by both contact and ingestion. Halofenozide works by mimicking the hormone that regulates insect molting. Chemical prevention treatments work best when applied before the grubs hatch.
Prevention treatments are referred to as season-long control, because the chemical lasts a longer time in the soil and targets the grub when it is small. Application of prevention treatments can be up to three months before the grubs are in their larval stage; however, they must be applied before egg-laying. Both imidacloprid and halofenozide have a low toxicity.
Curative controls are a fast-acting, short residual insecticide. Curative controls are applied in late summer when grubs are present. Curatives work better than chemical preventatives when grubs are larger. For better results, remove thatch and mow the lawn before treatment. Once the treatment is spread on the lawn, water it into the soil. Whether you use curatives or chemical preventatives, always follow the manufacturer's instructions.
Beneficial nematodes, such as the species Heterorhabditis bacteriophora, are microscopic, earth-friendly worms that are an alternative to chemical products. Release nematodes every two to three weeks in the spring, beginning when the soil temperatures reach 50 degrees Fahrenheit. Stop when the infestation subsides. Nematodes seek out their host and kill the larvae by emitting an endotoxin.