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Japanese Beetle Grubs The grubs of Japanese Beetles and their relatives (European chafers, Asiatic garden beetles, oriental beetles) are active in the soil during April and May and again from early August through October. The grubs are cream-colored and normally C-shaped, with a brown head and three pairs of legs. The easiest way to sample for grubs is to dig a square about 6 inches on a side and about 4 to 6 inches deep. Flip the sod upside down onto a flat surface (a plywood sheet does nicely). Use a hand trowel to break up clumps of soil in the ground or attached to the roots. Remove any grubs you find and put them in a plastic cup to count after you have finished. Be sure to beat the soil and roots on the bottom of the sod with the edge of the trowel. Many grubs will congregate in the thick roots just below the thatch, or will be just in the thatch, near the soil line. In the spring (April and May) and again in autumn (September and October), the grubs will be at least 1/2 inch long and very easy to find. In late July and early August, they will be much smaller and very close to the root-thatch interface, so you must look very carefully. Normally a healthy turf should be able to tolerate at least 8 to 10 grubs per square foot without visible weakening. If there are other stresses (such as drought, heavy traffic), the turf may be weakened with as few as five grubs per square foot. Note that some species of grubs are more aggressive or damaging than others. As a general rule, European chafers cause more damage than other species and so the tolerance level will be slightly lower. GreenShare Factsheet on white grubs Chinch Bugs Chinch bugs are small, relatively soft-bodied insects which remain active in the thatchy area just above the crowns of the turf plants. They are most easily monitored by using three of four empty coffee cans which have had both ends removed to leave an empty cylinder. Stick one end of the cylinder into the soil down about 2 or 3 inches (you may have to pound the can in with a mallet or soften the soil a little first by watering the area). Fill the cylinder with water (if possible, use a garden hose with moderate pressure) and wait about five minutes. The chinch bugs will float to the surface of the water, where you can count them. Chinch bugs are most active in sunny areas with some water stress. Conduct your sampling at the edges of droughty patches. Sampling should be conducted from mid June through the end of August. GreenShare Factsheet on chinch bugs Sod Webworms Sod webworms are caterpillars which reach an inch in length and feed on the blades of grass. Sod webworms feed actively at night and are virtually impossible to find during the daytime if you merely inspect the turf. However, webworms can be irritated to the surface by using an "irritating drench". Put one or two tablespoons of a dish detergent in two gallons of water and pour this solution over an area roughly two feet by two feet. The detergent solution irritates webworm caterpillars to leave their burrows and come to the surface within five minutes where they can be counted. Sample in July and August. If you sample at mid-day on a hot, sunny day, rinse the area with clear water after you have completed the drench test. Otherwise the soapy solution might burn the turf. GreenShare Factsheet on sod webworms Bluegrass Billbugs Bluegrass billbugs can cause serious damage to lawns, particularly those which are predominantly bluegrass. However, they occur sporadically in New England. The easiest way to sample for billbugs is to walk along the driveway or sidewalk on a warm, sunny day in late May to mid June. Bend over and observe insect activity on the pavement. Bluegrass billbug adults are black beetles with very elongated "snouts". The total body length is about 1/4 to 3/8 inch (6-9 mm) and the tail end is somewhat pointed. If you find an average of more that two billbugs for each minute of your search, the likelihood exists that those adults will produce enough offspring in the coming month to cause visible damage to the turf. In addition, billbug larvae deposit fecal matter which looks very much like sawdust into the thatch. If a finger inspection of the turf reveals sawdust-like material, this serves as a strong indication that billbug larvae are present. Usually the larvae themselves will be found in the lower part of the thatch. Inspect the area in a manner similar to that described for white grubs. Larvae are active from late June through August. GreenShare Factsheet on billbugs Other Insects Othe insects will be observed during your inspections. Keep in mind that many of these are actively beneficial, either by feeding on some of the pest species or by playing a significant role in the breakdown of organic matter in the food chain. One of the most commonly observed insects in a lawn is the ground beetle. Actually, there are many species of ground beetles, each of which is an active predator on a variety of soft bodied insects. One of the most common species is about 1/4 to 3/8 inch (6-9 mm) long, somewhat broad and flattened, with a very shiny coppery color. This insect moves rapidly along the surface of the turf, especially on sunny days.
Adapted from the University of Massachusetts Extension, 1999
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