Pest of the Month – White Grubs

White grubs are immature scarab beetles. They hatch from eggs laid in the soil, have three larval instars, and also pupate in the soil. The third instar is often the most damaging and may be present in the soil the longest. The adults are rarely turf pests, but some may feed on tree leaves or make mounds in the soil. White grubs may have one or more generations each year in Florida.

Signs of Infestation

When white grubs feed on grass roots, the grass gradually thins, yellows, and dies. This makes the grass feel soft and spongy. Scattered, irregular, brown patches of grass appear, which increase in size over time. The root injury reduces the turf’s ability to take up water and nutrients and withstand drought stress. Heavily infested grass pulls up easily.

In addition, white grubs attract moles, raccoons, armadillos, and birds, which can make an already damaged area look worse. However, these animals may be interested in earthworms or other insects besides grubs. Large numbers of dark-colored, parasitic wasps with yellowish to white stripes on their abdomens that hover over the lawn on sunny days in the summer or fall may also be a sign of infestation. Sample the area to confirm that a white grub problem really exists.

Life Cycles

The masked chafers have 2 generations each year throughout Florida, and the first generation is the most damaging. Adults are tan, about 5/8 inch long, and slightly smaller than May/June beetles. Adults fly from April to June and again in August and September. They are attracted to lights at night, but do not feed. Adults lay their eggs in the top inch or two of soil, often in small clusters. Small grubs hatch from the eggs and feed on grass roots. Most damage occurs from the first generation by July or August. The raster pattern is indistinct and does not have any rows of short, thick hairs. They pupate in earthen cells.

Sugarcane grubs have a 1 year life cycle. The grubs attack sugarcane, most warm season turf grasses, and some ornamental plant roots. Peak adult emergence occurs in May and June in southern Florida, but may begin in April and end in late July. Eggs are white and round. Small grubs are dark gray and whiten as they grow. Third instar (mature) grubs are present and feeding from September to late spring, and are nearly 2 inches long. The larvae have rusty-red colored head capsules, and their raster pattern looks similar to that of masked chafers. Pupae are tan-colored. Adult beetles are about 1 inch long, and are nearly black, with tiny horns behind the head (on the pronotum). This species is most damaging along the Gulf and Atlantic Coasts. A sister species, T. cuniculus, is increasing in abundance in southeastern Florida. The larvae look nearly identical to sugarcane grubs, but the adults are present every month of the year, with greater activity during the summer. These adults are more hairy than sugarcane grub adults.

We do grub preventative treatments in May and June that last throughout the grub season. Call us today to schedule your lawn treatment and have guaranteed protection against these pests.