Kentucky bluegrass, northern Utah's most typical lawn grass, is greening up and growing. At the Utah State University Extension office in Salt Lake City, we hear more and more questions about lawn pests and problems. Common insects damaging Utah lawns include grubs, billbugs and sod webworms. Damage is also caused by non-insect problems, including dog urine, thatch build-up and shallow rooting. Before applying any pesticide, positively identify the pest and then select the most environmentally friendly control possible. Good turf maintenance promotes lawn vigor and repels pests.
GO AWAY, GRUBS. Grubs are masked chafers, May/June beetle or black turfgrass ataenius larvae living underground, feeding on roots and dead plant material. There are many species of grubs, and they are an important part of the food chain.
However, when grub populations exceed about 15 per square foot, turfgrass suffers visible damage. Grub infestations are indicated by easy lifting of turf, late summer drought stress, and presence of the grubs or signs of natural predators. Skunks eat grubs, digging for them with their front clawed feet. The damage from skunks is usually worse than the damage from the grubs. Grub infestations are usually accompanied by a thick thatch layer, the spongy fibrous layer between grass blades and the soil surface. Thatch is best controlled with regular core aeration.
BE GONE BILLBUGS. Billbugs are weevils that damage many types of grass. These insects are about - to -inch long, black, with a snout nose. You may see them crawling across sidewalks or on paved edgings. The adults lay eggs at the base of grass blades. After eggs hatch, the larvae feed inside the crown of the plant. Larvae also may move down into the soil and feed on shallow roots.
Billbugs in Utah may be the bluegrass billbug or the Denver billbug, and the lifecycles of these two species are very different. Natural predators include birds, wasps and other insects. Chemical control of billbug larvae is not very effective. Instead, an organic control by parasitic nematodes, Steinerema carpocapsae, will help kill these larvae. While grub-damaged turf can be rolled up like a rug (because the roots have been eaten away), billbug-damaged grass is easily pulled away from its root system, with the blades severed at crown level.
NO MORE MOTHS. Sod webworm is a name given a large group of moths that feed on grasses in the larval stage. These larvae are caterpillars, living in a silken tunnel at the base of grass plants, leaving their shelter at night to feed on blades of grass. Infested areas begin to look thinned and tattered. The tunnels or larvae, or both, can be discovered when the lawn is inspected. Predatory insects, including ants, ground beetles and parasitic wasps, are effective in controlling sod webworm. Minimizing use of insecticides will keep a healthy population of these predators.
MAINTENANCE RESOURCES. Good turfgrass maintenance, including annual aeration, proper irrigation, regular mowing at an appropriate height and fertilizing at the correct rate, will help your lawn stay healthy and resistant to severe pest infestations. If you suspect your lawn has insect problems, inspect it carefully and take a pest specimen to the USU Extension office for identification. Then use the most efficient control method and work at improving lawn vigor.
More information about lawn care is available online at the USU Extension Web site. Links to online lawn insect information are available at the Salt Lake County USU Extension Web site.
The author is an assistant professor for Utah State University Extension in Salt Lake County. Her area of expertise is horticulture. E-mail her at maggiew@ext.usu.edu.