Tip Sheets

Beetle Grubs

Beetle grubs are a major cause of lawn damage each spring and fall in our area Grubs are the larvae stage of beetle cycles. Adult beetles lay eggs from early to mid summer. In a short time the eggs develop into grubworms which begin to feed on grass roots from mid summer until fall's cooler soil temperatures force them to seek refuge at deeper soil depths. The grubs then hibernate until spring temperatures warm the soil. They then resume feeding until they pupate or "hatch" into mature beetles anywhere from late May through mid July.

The Damage

The resulting damage (which may take not start showing until the summer or early in the spring) appears as brown patches of dead turf that enlarge as the grubs continue to feed. To check for grubs pull at a section of dead turf. It will roll back like a swatch of carpet. Dig down at the edge of a damaged area and you will find the grubworms themselves; grayish, white grubs with gray or brown heads, approximately 1/2" to 3/4" long. They will be curled into the shape of the letter "C". Immature grubs are milky gray in color and resemble elongated eggs. They will be about 1/4 inch long.

Grub Control

There are many variables in trying to achieve maximum grub control, including the type of grub, the timing and type of insecticide, the amount of thatch, and how well the insecticide is watered into the soil. Remember that maximum control is usually 80% to 90%. An otherwise healthy lawn can tolerate 4-6 grubs per square foot without showing grub damage.

It is essential that any insecticide you apply be watered in immediately and thoroughly after application. Water each area treated for at least one hour.

The best time to treat for grubs is mid-April to mid-May and mid-August to mid-September. Grub cycles will vary from year to year, so it is best to consult your garden store expert to determine proper insecticide and timing for application.

What about Moles?

Although mole activity may signal grub infestation, moles feed on a variety of soil insects. Eliminating grubs may convince moles to move elsewhere, but other controls should be used to solve the problem.