Turf insects: damage and scouting
White grubs
Several species of grubs occur in New England. The most widespread species is the Japanese beetle. The European chafer is found in several locations in eastern and western Massachusetts (especially “inside” Route 495, and along the coast as far north as mid-coast Maine). The Oriental beetle is active in Connecticut, Rhode Island, coastal Massachusetts, and along the Connecticut River Valley. As a general rule European chafers and Oriental beetles are harder to manage than Japanese beetles. In addition, there have been a few occasions where Asiatic garden beetles have caused damage, although the damage from this species is usually most severe in less well maintained turf.
Management of white grubs is most efficient when the specific population causing turf damage is identified. Because some insecticides are less effective against Oriental beetle or European chafer, species identification has become increasingly important for management decisions. Identification of a white grub is made based on its raster pattern. A raster is the pattern of bristles on the underside of the last abdominal segment of the grub. Refer to Figure 1 for illustrations of the various grub rasters.
Damage - Damage from white grubs initially resembles drought stress, with general thinning and/or yellowing of turf. In some circumstances, skunks, raccoons or birds may tear apart turf in infested areas to feed on grubs near the surface, often dramatically increasing the extent of the damge.
Scouting - Use a shovel or spade to cut three sides of a square in the turf anywhere from 6” to 12” on a side, 3” to 4” deep. Flip the sod back on the uncut (fourth) side, turf side down, and use a hand trowel to dislodge soil in the soil/thatch interface. Alternatively, you can use a golf course cup cutter (4.25” diameter) to collect soil samples. The cream colored grubs will be very visible against the dark soil background. Place grubs in a container and count them after removing all of them from the sample area. Convert the area to square feet (e.g., 6” sides = 0.25 sq. ft.). Note that a standard golf course cup cutter is equivalent to 0.1 sq. ft. Take several samples and then calculate the average number of grubs found. For ease in averaging, make all sampling cuts the same size.
Note that weather and soil moisture conditions will affect grub behavior and movement. In very dry or very warm conditions, grubs will move deeper in the soil profile (so sampling holes must be dug deeper). In very moist conditions, grubs will either be closer to the surface or will move laterally to higher or better draining locations.
In the autumn or in early spring, grubs respond directly to soil temperatures. European chafers tend to remain in the root zone later in the fall and return to the root zone earlier in the spring than other species of grubs. Japanese beetles and Oriental beetles tend to respond to daily temperature fluctuations. On warm days in late fall or early spring, the grubs will move up into the root zone and feed, while on cold days or after very cold nights, grubs will remain several inches below the soil surface.
Figure 1. Raster patterns of turf-infesting grubs (drawings not to scale).
Adapted from Haruo Tashiro: Turfgrass Insects Of The United States And Canada. Copyright (©) 1987 by Cornell University. Used by permission of the publisher, Comstock Publishing Associates, a division of Cornell University Press.
Black turfgrass ataenius
The black turfgrass ataenius (BTA) is a small species of white grub. The BTA life cycle is quite different from other grubs. It spends the winter in the adult stage, and females lay eggs in late spring. These eggs hatch into small grubs that feed throughout the month of June and into early July. In many years the grubs pupate and the new adults lay eggs in late July for a second generation. Black turfgrass ataenius is only a pest of concern on golf courses and other very low-mown sports turf (i.e. tennis, croquet) in New England.
Damage - Damage resembles that of other white grubs. Roots can be destroyed and damaged turf may peel back easily. Damage sometimes is more severe in areas with high levels of soil organic matter.
Scouting - Grubs can be found by taking a soil sample, cutting a small section of turf to a depth of 2” to 4” and inspecting the soil for tiny (less than 0.5”) grubs. Adults often are seen on the surface of putting greens, especially on warm sunny days in the spring. To scout for adults, force them to the surface with a soapy flush (irritating drench).
Chinch bugs
The hairy chinch bug (Blissus hirtus), the most common species in the Northeast, prefers ryegrass and fescues but will attack other lawn grasses as well. Adult chinch bugs are about 1/5-inch long and black with white markings on the wings. Nymphs (immature stages) have the same general shape as the adult but lack wings and often have red or orange markings.
Damage - Damage is often confused with drought stress, and normally occurs during July and early August. Injury (wilted or browned out areas) is most severe in sandy soils and in sunny areas. Small patches gradually coalesce into large areas of wilted or dead turf. Chinch bug-damaged turf may not recover in September when other turf comes out of drought dormancy.
Scouting - Use a cup cutter or similar device to remove cores of turf about 4” to 6” in diameter, place the cores in a bucket, and fill the bucket with water. Wait about five minutes. Chinch bugs (and big-eyed bugs, a beneficial insect) will float to the surface of the water. Chinch bugs can also often be observed directly by inspecting the foliage and thatch.
Sod webworms and cutworms
Sod webworms and cutworms are moths that cause damage to turf in the caterpillar stage of their development. In webworms, the color pattern varies with the species and plant source, but most are greenish, grayish, or brownish, and usually have dark spots scattered along the body. The black cutworm, the most common cutworm species in New England, is normally dark gray or nearly black but may have a hint of green in the stripes. Webworms are more likely to cause damage in lawn settings, while cutworms are more frequently encountered on golf courses and other closely-mown turf areas.
Damage - Damage usually begins as small discrete brown patches which can coalesce into larger areas of damage. A finger inspection of the infested area will sometimes reveal sod webworm burrows lined with green frass (insect excrement). Cutworms are often active around aerification holes on golf course greens.
Scouting - Prepare an irritating drench by mixing one fluid ounce of lemon scented dish detergent in one to two gallons of water in a pail. Spread this solution over an area about 2’x2’. Wait three to five minutes. Webworms and cutworms (and earthworms) will be irritated by the soapy solution and will crawl to the surface of the turf area. Note: The soapy solution can burn turf, so on sunny days, and on bentgrass or Poa annua turf, rinse the sample area with clear water after you have completed the insect count.
Annual bluegrass (Hyperodes) weevils
The annual bluegrass weevil (Listronotus maculicollis, also sometimes referred to as the Hyperodes weevil) is a significant golf course pest in many parts of the Northeast and Mid-Atlantic states. Annual bluegrass weevil is only a pest of concern on golf courses and other very low-mown sports turf (i.e. tennis, croquet), and is not found in higher-cut turf. The insect overwinters in the adult stage. Adults emerge in the spring and migrate from overwintering sites to lay eggs in turfgrass leaf sheaths (almost exclusively annual bluegrass). Following egg hatch, feeding of the tiny larvae becomes increasingly more aggressive up until pupation and the final transition to the adult stage. The annual bluegrass weevil may complete two or three generations per year in New England.
Damage - The most severe damage normally occurs from early June through mid-August, with moderate damage possible at other times of the summer as well. Damage begins as small yellow patches, often along the edges of fairways or on collars around greens, and spreads into large areas. Severely damaged areas take on a water-soaked appearance. Damage is most often restricted to short cuts (fairways and shorter) of annual bluegrass. However, field observations have confirmed that annual bluegrass weevils will feed on creeping bentgrass under certain conditions.
Scouting - Use a cup cutter or similar device to collect cores of 4” to 6” diameter. Loosely break up the soil in the cores and place the loosened soil and all plant matter in a dish pan or similar plastic container. Fill the container with lukewarm water and wait about five minutes. Weevils in all stages of development (except eggs) will float to the surface of the water, where they can be counted. You can also use a saturated salt solution to force larvae to the surface of the water. Large larvae and pupae are visible in turf samples without using flotation techniques. A leaf blower can be reversed and used to vacuum adults from an infested area. Insert a gauze bag in the end of the tube to collect the insects.
Bluegrass billbugs
Bluegrass billbugs can cause serious damage to lawns, particularly those which are predominantly bluegrass. They occur sporadically in New England. Billbug adults are black beetles with very elongated “snouts.” The total body length is about 1/4-to 3/8 -inch and the tail end is somewhat pointed. Despite the name, bluegrass billbugs will feed and even thrive on most cool season turf species.
Damage - Look for evidence of damage along the edges of paved areas in mid- to late July. Bluegrass billbug infested areas begin to wilt but do not respond to watering. As larvae feed in the stems and on the roots, damaged turf can be tugged loose with very little force. Infested areas will brown out entirely in a matter of several days. Damage is usually most severe in July and August. Damaged turf often does not recover in September and renovation may be necessary.
Scouting - Larvae can be found by digging into the root/thatch interface with a hand trowel and inspecting the area. Accumulations of “sawdust-like” material (billbug excrement) will be found in the thatch.
Invasive craneflies
The European cranefly (Tipula paludosa) is an invasive species that has become a pest in western New York and southern Ontario (Niagara Peninsula). The common (or marsh) cranefly (Tipula oleracea) is another invasive species that has become established in western New York and Long Island. T. oleracea has been recently reported from several areas in Massachusetts, including Martha’s Vineyard, Cape Cod, and several suburbs south and west of Boston. Adults (which resemble large mosquitoes) emerge in late August or September. Females lay 200 to 300 black eggs near the soil surface. Small larvae feed from October through February, (when temperatures are mild). Larvae normally feed in the top inch of the soil, feeding on roots and root hairs. Larvae can be found within 3 inches of the surface, even in the winter months (larvae wriggle to the surface and can be seen projecting out of the turf. They pupate mid-March to mid-April. New adults emerge, lay eggs, and the resulting larvae feed through the summer months. They pupate in mid- to late-August, and adults emerge in September to complete the cycle.
Damage - Damage may resemble grub damage, especially in higher cut turf, because the larvae destroy roots. Animals and birds may cause turf damage while foraging for the larvae, as is also frequently the case with white grubs. On closely-mown turf, such as tees and greens, the damage might resemble cutworm feeding or aerification holes with the edges nibbled away.
Scouting - Watch for flights of ‘large mosquitoes’ in the spring and late summer. For larvae, take a soil sample (a cup cutter plug to a depth of about six inches often works well) and break the soil apart. The larvae are olive green to dark brown and quite active, often within the top inch of soil or in the thatch. Larvae can occasionally be seen at the surface feeding on turfgrass foliage on warm, humid nights.
Ants
Ants can be beneficial because they are often predators of other insects.
Damage - Several species of ants occur in turf and can disrupt the surface when building mounds. The turfgrass ant (Lasius neoniger) forms numerous mounds of 0.5” to 2.0” diameter on closely mown turfgrass, such as golf course fairways. These mounds are unsightly and can dull or damage mower blades. In the process of building tunnels, ants can break off roots and root hairs or increase desiccation of the soil.
Scouting - Rough estimates of ant activity can be obtained by counting the number of mounds in a given area.
Insect threshold levels
The key to any Integrated Pest Management program is the identification of response (or “action”) threshold levels. There is no single magic number which will be appropriate for all turf situations. Thresholds are given as first approximations only, and should be used only as guides.
Several agronomic factors will have a direct effect on the number of insects a turf area can tolerate. Some of these factors include the species of turfgrass, the height of cut, availability of irrigation (and resulting soil moisture distribution), use patterns (including traffic and other sources of compaction), and the fertility program. The thresholds presented in Table 14 are for unirrigated turf and are provided as guidelines only. In most cases, irrigated turf can sustain higher insect populations without showing stress.
Actual response thresholds will depend on the overall vigor of the turf being managed, the use of the turf, the presence of secondary pests such as skunks and raccoons, and the quality expected.
| INSECT | Approximate threshold per sq. ft. |
|---|---|
| Japanese beetle | 8 to 15 larvae |
| Oriental beetle | 8 to 15 larvae |
| Masked chafer | 8 to 15 larvae |
| European chafer | 3 to 8 larvae |
| Asiatic garden beetle | 12 to 20 larvae |
| May beetle (Phyllophaga) | 2 to 4 larvae |
| Black turfgrass ataenius | 15 to 80 larvae |
| Annual bluegrass weevil | 10 to 80 larvae |
| Bluegrass billbug | No good estimate available |
| Chinch bug | 30 to 50 nymphs |
| Sod webworm, cutworm | No good estimate available |
| * Please note that actual threshold levels will vary based on site conditions, management practices, and/or turf use. | |