They stay below the surface, often unseen unless you dig to install plants or hardscapes. The bloated larvae of common beetles are a normal part of the ecosystem in most lawns and no cause for alarm in small numbers. In higher numbers, however, they can inflict visible harm on turfgrass.
Learn to identify indigenous white grubs and their damage to determine whether or not intervention is necessary.
Clues to White Grub Problems:
The first clue of a potential white grub problem can be found in the summer’s beetle population. White grubs are the larvae of green June beetles, Japanese beetles, May or June beetles, and chafers. If you notice an unusually high number of these pests buzzing around a client’s home this summer, their lawn may serve as a banquet to their offspring in the coming months.
Grubs feed below the soil surface, primarily feasting on turfgrass roots. Since roots supply water and nutrients to the grass blades, grub damage typically results in yellow or brown leaves.
The effect can mimic drought stress, even when rain or irrigation is plentiful. Heavier infestations result in loose turf that can be easily lifted from the soil and a spongy feeling underfoot, similar to freshly laid sod.
Animals like skunks, racoons and armadillos enjoy eating grubs, which might be beneficial if not for the unsightly holes they leave behind. To reach the grubs, the critters tear through the sod, rooting around in the soil on the hunt for their intended meal. Rather than attempting to control hungry skunks, racoons or armadillos, treating the grubs will likely prove more effective.
Verify the Infestation
If a lawn suffers from one or more of the previously mentioned issues, you can confirm the presence of grubs by inspecting a one-foot section of soil under the turfgrass. The day after a rain or irrigation, cut through the grass on three sides of a one-foot square with a shovel and roll the sod back. You may need to dig down about four inches or so, depending on the variety of grub. Sift through the soil thoroughly and collect, identify and count the grubs you find.
Identification and Control
All white grubs look similar with fat, nondescript whitish bodies, making identification difficult. If you’re squeamish, enlist a pro to help you identify and treat the grubs. If you don’t mind handling them, match the grub to the photos below, and closely follow the directions on the appropriate insecticide label.
Green June Beetle
These grubs have tiny legs out of proportion to their overall body size. Examine the soil four inches down. A count of six or eight per square foot warrants treatment.
Unlike other grubs, the larvae of Green June beetles emerge from the soil to feed at night, so you may notice small mounds of dirt left behind. This habit also makes them easier to control, since they readily come into contact with the insecticide.
Look for randomly scattered spines on the raster (tail end). The grubs will be found in the top two to three inches of soil, and presence of more than 10 grubs per square foot warrants treatment. Treat after irrigation or rain, and apply another half inch of water after treatment to help ensure the insecticide reaches the grubs.
Not only do these grubs cause turfgrass damage, but they also grow into beetles that eat the leaves, flowers and fruits from a wide variety of trees and plants in landscapes and gardens.
Sporting a distinct “V” shape in the spines on the raster, the grubs of Japanese beetles are usually found in the top one to two inches of soil and in the grass roots. Ten or more per square foot indicate the need for treatment. Treat after irrigation or rain, and apply another half inch of water after treatment to help ensure the insecticide reaches the grubs.
May or June Beetles
Also known as June bugs, the raster of these grubs are marked with distinct parallel rows. Dig into the soil three to four inches to find and count them. If they number ten or more per square foot, treat after irrigation or rain and apply another half inch of water after treatment to help ensure the insecticide reaches the grubs.
White Grub Treatment
Keep in mind, unless the turfgrass sustains damage, treatment of white grubs is generally not necessary. However, if damage occurs and the grub count of a specific beetle is high, contact your local Extension Service for recommendations on appropriate insecticides.