Lawn Pests in North Dakota

E-904 (Revised), April 1997
Phillip Glogoza, Extension Entomologist

Even the most beautiful lawns can be troubled by pests. To maintain a healthy lawn, homeowners and lawn care professionals must be able to recognize the symptoms of pest damage and be able to identify the pest and understand its life cycle in order to apply appropriate and effective controls. This circular discusses the life histories and control strategies of the common invertebrate lawn pests of North Dakota.

Sod Webworms
White Grubs
Ants
Earthworm
Other Pests Associated With Lawns
Additional Readings

Sod Webworms

Sod webworms are a complex of several species of moths in the family Crambidae with similar biologies and appearance. Damage to lawns is caused by the larval or caterpillar stage.

Damage Symptoms: Sod webworm lawn damage is caused by the larvae feeding at night on the leaves, crown and roots of grass and is usually first noticed during periods of hot dry weather as grasses become dormant. Prior to the appearance of browning, homeowners may notice large numbers of robins, blackbirds, grackles or flickers feeding in concentrated areas. Brown irregular spots and later ragged uneven patches of grass are the first indications of lawn damage. The grass on the edge of dead patches is short or uneven from the feeding activities of the larvae. A search for the larvae should concentrate in the thatch of the margins of dead patches since this is where active feeding occurs. If the infestation is heavy, large areas of grass may be damaged severely or destroyed in only a few days. Sod webworm moths do not feed on lawns but are frequently observed flying over the lawn on calm evenings as they move about to lay eggs.

Sod webworms have a preference for newly seeded, thick lawns. They prefer bentgrass, bluegrass, fescue and timothy, as well as pasture and field grasses.

Biology and life cycle: Sod webworm moths (Figure 1) first appear in late May to early June and range from 1/2 to 3/4 inch long and are whitish-gray or brown. They fold their wings tightly over their bodies at rest and have a prominent projection on the front of the head that forms a distinctive snout. At rest on the grass, they resemble pieces of a wooden match stick attached to a grass blade. The front wings are triangular, narrow and have a distinctive wing scale pattern. The front wing scale pattern may have a distinctive silver, white or black longitudinal streak. The hind wings are broad and lack distinctive markings. During the day, moths hide in shrubbery and dense turf near the soil and seldom move until disturbed, moving a short distance from their original roost. Toward evening, mated females fly about the lawn and lay their eggs in the grass crowns. Each female may lay several hundred eggs over a period of one to 10 days.

Figure 1

Eggs are small, oval and white when first laid but turn pale yellow to bright scarlet before they hatch. In one to two weeks, the eggs hatch and the first stage larvae begin to feed on grass. The larvae (Figure 2) are active, thick bodied and 1/4 to 1 inch long. The head is dark brown and the body is grayish to milky white, often with dark spots. Each larva constructs a loose silken web, containing bits of debris, on the surface of the ground, which leads to a silk-lined tunnel at the base of the plant where the larva lives (Figure 3). Larvae emerge from their tunnels at night to collect blades of grass which they pull into their tunnels and feed upon. Some feeding may occur on the roots and crowns of the grass and noticeable thinning of the lawn will be apparent. After the larvae have reached maturity, they burrow into the soil and spin a silken cocoon where pupation occurs.

Figure 2	Figure 3

Pupation lasts about 14 days, with the pupae ranging from 5/16 to 1/2 inch long. Initially they are light yellow but, as they mature, they become dark brown. The moths then emerge and start a new generation. In North Dakota, sod webworms have one to two generations per season. Webworms overwinter in the egg stage or as larvae within special chambers in the soil known as hibernacula. Larvae emerge from these chambers or hatch from eggs in the spring to continue the life cycle.

Natural enemies: Natural enemies of sod webworms, such as disease, parasites and predators, keep most populations below damaging levels, but if notable damage develops, chemical control measures may be necessary.

Sampling methods: The presence of adult sod webworms may be determined during walks through the lawn or while mowing the lawn. The moths emerge from the grass and fly about 2 to 4 yards with a quick, jerky, zigzag flight before again landing. Adult moths do not damage the lawn, so sampling for larvae is recommended.

Webworm infestations may also be determined by breaking apart 6-inch square sections at the edge of dying sod. Control of larvae is recommended if an average of three to four larvae are found per 6-inch square section of sod. See control table for chemicals registered for sod webworm control.

Cultural practices: Cultural practices will not control webworms in lawns. Sod webworm problems in lawns are most apparent from July to September as larval populations increase and the growth of grass slows down. Routine lawn care will aid the lawn in withstanding damage and will aid recovery from damage but will not stop the feeding activity of the larvae. The development of resistant strains of grass may provide a future means of reducing or stopping larval damage.

White Grubs

White grubs are the larval stage of June beetles (Scarabaeidae: Phyllophaga spp.). The different species of white grubs that infest lawns cause similar turf damage and are similar in appearance.

Damage symptoms: Grub damage in lawns occurs when larvae feed on the roots of grass causing the grass plant to turn brown and die. The size of the brown patches varies depending on the number of larvae feeding in a particular area. Dead patches become more noticeable as the summer growing season progresses. Feeding damage of grubs separates the turf from the roots so effectively that the turf and thatch can be rolled or pulled up like carpeting, often exposing the larvae below. The larvae also damage the roots of pasture grasses, corn, small grains, strawberries, potatoes and other garden vegetables.

In areas with large June beetle populations, adult feeding may cause minimal defoliation in flower beds, shrubs (e.g. dogwood and honeysuckle) and trees (e.g. bur oak, birch, hackberry, willow, elm, ash, poplar and cottonwood).

Biology and life cycle: The life cycle of June beetles varies from two to four years depending on the latitude and the particular species. The majority of species inhabiting North Dakota have a three-year life cycle (Figure 6). The cycle begins when adults emerge in late May or early June. Adult beetles (Figure 4) are oval and robust, tan to dark brown and 1/2 to 1 inch long. The wing covers are hard and may be smooth and shiny or covered with short hairs. Newly emerged adults mate and the females burrow 3 to 7 inches into the soil to lay eggs. Each egg is placed in a cavity in the center of a ball of soil. A single adult female will lay about 50 eggs during her life. The eggs are pearl white, oblong and approximately 1/10 inch long. Eggs hatch in three to four weeks into milky white first stage "C-shaped" larvae (white grubs) which will grow to about 1 inch long by maturity (Figure 5). The larvae have a hard brown head capsule with a soft, shiny, creamy-white transparent body which is dark gray to blackish at the rear portion. Six prominent brownish legs are present right behind the head. The newly emerged larvae move upward in the soil to the root zone of the grass to begin feeding. The larvae feed on the roots throughout the summer. In the fall, they burrow deeper into the soil to hibernate during the winter. The larvae move upward and resume feeding on grass roots the following spring (Figure 6).

Figure 6 (36KB b&w illustration of life cycle)

Figure 4	Figure 5	Figure 7

The larvae feed throughout the second summer, burrowing deep into the soil in the fall to hibernate. During the following spring, the larvae feed for a short period, burrow back into the soil and form earthen cells for pupation. During this nonfeeding stage, the pupae (Figure 7) transform into adults. Pupation will be completed during the third summer but the adults do not emerge until the following spring. The three-year cycle is repeated when the adults emerge.

Natural enemies: There are several natural controls that may effectively reduce the grub populations to levels where chemical control is not required. White grubs are susceptible to infections by viruses, bacteria, fungi, parasitic nematodes, parasitic mites, parasitic wasps and parasitic flies. Vertebrate predators such as crows, woodpeckers, grackles, gulls and skunks will rout for grubs in infested lawns.

Sampling methods: In areas where June beetles are a problem, light traps (or porch lights) may be used to monitor adult emergence. The adult beetles are nocturnal and males are attracted to light. Insecticides applied to the lawn at the time of beetle emergence will kill the females as they burrow back into the ground to lay their eggs.

Sample for larvae by removing strips of sod 1 square foot by 3 to 4 inches deep and counting the number of larvae. Samples should be taken from several areas of the lawn representing both healthy and affected areas. Control should be initiated when there are an average of three to four white grubs per square foot.

Cultural practices: Regularly scheduled lawn maintenance is a good means of deterring the activities of the larvae. Adult egg-laying females are attracted to bare patches or thinned out areas on the lawn. Maintaining a healthy lawn by proper cutting, fertilization and dethatching makes the lawn less attractive to the egg-laying females. If the lawn again becomes infested, it is better able to withstand damage and recover.

-- M O R E --

E-904 (Revised), April 1997