Insect pests of home lawns in Georgia
Importance of Pests
Home lawns in Georgia are commonly infested with insects and related arthropods. Most of these creatures go unnoticed by the homeowner, however several species cause serious damage to turfgrass. These pests can be divided into two groups based on where they are found: soil inhabitants and thatch inhabitants. Both groups can severely damage turf. A knowledge of pest biologies, life histories and habits is needed before effective control programs can be implemented.
Nature of Damage
Damage to turfgrass from insect pests takes many forms. Feeding by soil-inhabitants such as white grubs, billbugs, and mole crickets usually shows up as wilted, dead or dying grass. Sod may be disturbed in areas where wildlife or pets dig up soil-inhabiting pests. Damage to turf by thatch inhabitants such as sod webworms, armyworms and cutworms is apparent when grass is cut off close to the ground. Damage by chinch bugs and spittlebugs, also thatch inhabitants, is similar to damage caused by soil inhabitants. Irregular spots of yellowish turf and dead spots may occur where chinch bug or spittlebug infestations go uncontrolled.
Due to the variation in symptoms of damage, insect pests must be correctly identified before the appropriate method of control can be chosen. Knowledge of the biology and life cycle of correctly identified pests is the key information needed to design an effective control program. Your local County Extension agent or other turf professional can provide assistance with identification of turf pests.
Pests - Identification, Life Cycle and Diagnosis
Soil - Inhabiting Insects
- Identification: Mole crickets are light brown, up to 1 1/2 inches long, have short, stout forelegs, spade-like feet, and large eyes. The young resemble the adults except that they are much smaller, have no wings and are sexually immature.
- Life Cycle and Diagnosis: Adults lay eggs in underground cells in the spring. The eggs hatch in 2 to 4 weeks, depending on the weather. Nymphs feed and grow through the summer, and mature into adults in the fall. Mole crickets spend the winter deep in the soil but come to the surface to feed during warm periods. Adult crickets leave the soil on warm spring nights to fly around, sometimes in huge numbers, looking for mates and egg-laying sites. There is one generation per year, and most adults die by early summer.
- The most damaging species of mole crickets feed on grass. With other species the majority of turf damage is related to their tunneling activity. Both young and adults burrow beneath the soil and make tunnels similar to those made by moles, but much smaller. This loosens the soil and causes it to dry out quickly, as well as clipping the roots of the grass plants. Left unchecked, mole crickets will build up in an area and completely destroy the grass, leaving bare ground.
- Identification: These grubs are plump, C-shaped insects with three pairs of legs. They are whitish with dark areas near the rear. They have a distinct, brown head. The adults are beetles commonly referred to as chafers, May beetles, June beetles, and others.
- Life Cycle and Diagnosis: Adult female beetles lay their eggs in the soil. The grubs hatch and spend most of their life beneath the soil feeding on underground plant parts. Most have rather long life cycles with the grub stages lasting from several months to two or three years. Grub feeding destroys the roots, leaving the tops to wither and die. In heavy infestations roots are pruned off to the extent that turf can be rolled back like a carpet.
- Estimate the grub population in your lawn to determine if treatment is necessary. Fall or early spring is the best time to look for grubs. At these times the grubs are near the soil surface feeding at the root zone. Use a spade to cut three sides of a strip one foot square by two or three inches deep. Force the spade under the sod and lay it back, using the uncut side as a hinge. Use a trowel to dislodge soil from the overturned roots. Count the grubs in the exposed soil. Replace the strip of sod. Following the same procedure, cut strips of sod in several other parts of the lawn and count grubs under each strip. Calculate the average number of grubs per square foot of lawn by dividing the total number of grubs by the number of strips. If the average number lies between 5 to 10 grubs in non-irrigated turf or greater than 20 grubs in highly maintained, irrigated turf, control measures may be required.
- Identification: Adult billbugs are weevils 1/5 to 3/4 inch long. The reddish-brown to black adults have a pair of jaws at the tip of a long snout or "bill." The young are white, legless grubs about 3/8 inch in length with the rear end wider than the head.
- Life Cycle and Diagnosis: Adults feed above ground and deposit eggs in the stems of host grasses. Hatching larvae feed within the stems; larger larvae feed on the crown; mature larvae feed on the roots of the turf. Zoysiagrass and bermudagrass are most often injured, but, feeding may occur on many grasses. In heavy infestations, roots of grass are destroyed and the turf killed in irregular patches. Damage from billbugs differs from white grub or mole cricket injured turf as infested soil usually stays firm.
Leaf, Stem and Thatch Inhabitants
- Identification: Spittlebug adults are about 3/8 inch long, dark brown or black, and have two orange stripes across their wings. The nymph is ivory-colored with a brown head. They live inside masses of spittle or froth, hence the name "spittlebug."
- Life Cycle and Diagnosis: Orange-colored eggs are deposited in bits of hollow stems and other debris. Nymphs hatch in about two weeks and begin to feed immediately by sucking juices from the grass. They cover themselves with a frothy mass known as spittle. There may be one or several nymphs in each spittle mass. The masses are found from just below the soil surface to a few inches above it. A heavily infested area will feel "squishy" when you walk across it due to numerous spittle masses. Centipede grass is especially prone to spittlebug infestation and populations often begin and increase in shady areas. In Georgia there are 2 generations of spittlebugs each year.
- Identification: Adults are about 1/5 inch long, light in color with small black triangular patches on the wings. The wings are carried folded over the back. The nymphs are from 1/20 to 1/5 inch long and vary in color from a reddish with a white band across the back to black as they near adult size.
- Life Cycle and Diagnosis: The eggs are laid in leaf sheaths or crevices in nodes and other protected places. The young develop into adults in four to six weeks. There are 3-4 generations a year. The bugs insert their slender beak into the grass and suck the plant juices. Typical injury appears as spreading patches of brown, dead grass. St. Augustine grass is the most seriously injured, but other lawn grasses are also subject to attack. Chinch bug infestations and damage are most often first noticed during hot dry periods in sunny areas of the lawn.
- Identification: Sod webworms are caterpillars of small brown to dull gray moths. Webworms grow to a length of nearly 3/4 inch and vary in color from pinkish white to yellowish brown with a light to dark brown or black head. They are covered with fine hairs. The moths have a wingspan of about 3/4 inch. They fold their wings closely about their bodies when at rest and have a prominent forward projection on the head.
- Life Cycle and Diagnosis: Moths hide in shrubbery or other sheltered spots during the day. They fly over the grass in early evening. The female scatters eggs over the lawns as she flies.
- Sod webworms feed only at night. Damaged grass blades appear notched on sides and are chewed raggedly. Irregular brown spots are the first signs of damage. Large areas of grass may be damaged severely. A heavy infestation can destroy a lawn in only a few days. Insecticide application should be timed for treatment two weeks after peak moth activity and should be made during early evening hours when caterpillars begin feeding on the surface of the turf.
- Identification: Armyworms, which attain a length of 1/2 inches, are also caterpillars of moths. Their bodies are greenish when small but become brown when fully grown. Several stripes are usually apparent, extending from the head to the rear. The adult is a mottled brownish-gray moth with a wingspan of nearly l l/2 inches.
- Life Cycle and Diagnosis: Moths lay clusters of eggs on grass blades, lawn furniture, white or light colored walls and other objects near lawns. Caterpillars hatch and begin to feed on the turf. Damaged turf appears ragged with individual blades showing signs of chewing damage. When numerous, they may devour the grass down to the ground. Caterpillars pupate in the soil. The moths emerge within a couple of weeks. They are active mainly at night. There are three to six generations a year. As with sod webworms, time insecticide applications to control armyworms during the early evening when caterpillars are feeding on the surface of the turf.
- Identification: Cutworms, also the caterpillar stages of certain moths, grow to a length of 1 1/2 - 2 inches. They are mottled dull brown, gray or nearly black and usually appear plump and greasy. If disturbed, the caterpillar usually curls into a C-shaped ball. The front wings of the moth are dark brown to gray, are mottled or streaked, and have a wingspan of 1 1/2 - 2 inches.
- Life Cycle and Diagnosis: Eggs are laid on grass and weed stems or behind the leaf sheath of such plants. Caterpillars usually remain below the ground surface, under clods, or other shelters during the day and feed at night. Foliage or stems may be cut off (hence the name cutworm) by the caterpillars. Cutworms pupate in the soil. There may be several generations in a year. Due to their nocturnal behavior, it is best to time control measures for early evening when caterpillars are present on the surface of the turf.
Control of Major Turf Pests
In Georgia, most insect pests of turf can be controlled when damaging populations are found. However, remember the first step to management of lawn pests is prevention. Good cultural practices are essential to prevent insect pests from destroying turf. Use recommended methods of fertilization, watering, mowing, etc., to keep grass healthy and growing vigorously. A healthy lawn can tolerate light insect infestation and damage is masked or overcome by rapid growth of plants. Current recommendations for growing and maintaining healthy turf are available from your local County Extension office.
Thatch removal is one means of preventing chinch bug and spittlebug outbreaks. Heavy thatch accumulation provides an ideal environment for these insects. Thatch also interferes with delivery of insecticides to the insects.
The next step to management of turfgrass pests is early detection. This is the weakest link in pest management programs for lawns as most insects go unnoticed until after their damage is observed. Two techniques useful in detection and monitoring insects in turf grasses include floatation and irritation. Floatation uses water to detect the presence of chinch bugs. Remove the bottom from an oil can, coffee can, or similar container. Push the can two to three inches into the turf in an area of suspected chinch bug infestation. Fill the can with water and hold the water level above the grass by adding additional water for about five minutes. If chinch bugs are present they will float to the top. (Sample several spots at the edge of the area where you suspect chinch bugs are damaging grass to increase the chances of finding the insects.) The irritation method is particularly useful in detection and monitoring of mole crickets, cutworms, armyworms or sod webworm infestations. Lemon dish washing detergent is a good inexpensive irritant. Mix the detergent with water and pour over a turfgrass area. The detergent irritates sensitive soil-inhabiting pests causing them to quickly come to the surface. Use one ounce liquid detergent per gallon of water. Use one gallon of water to sample a one square yard area of turfgrass. Pyrethrin is also a good flushing agent when used at a concentration of one to three percent in water.
Proper Selection of Control Materials
Materials labelled for insect control on home lawns are available in several formulations: baits, emulsifiable concentrates, wettable powders, soluble powders, and granules. The formulation selected, as well as the specific insecticide chosen, determine the level of control. For example, bait formulations are superior in spring and fall for mole cricket control, whereas summer treatments with sprays or granules give better control. Spray applications of insecticides provide the highest degree of control within the first 24 - 48 hours after application. In general, the initial control with granular treatments is less than that from sprays. Insecticidal activity begins only when the granule absorbs moisture and releases the insecticide. For specific insecticide recommendations on turf consult your County Extension Agent.
Correct Application Methods
Application methods are extremely important in turf insect control. The homeowner may use the most effective insecticide available, but if the method of application is poor, the level of insect control will be disappointing.
To control insect pests living in the soil, the target zone for the insecticide should be the soil at the root zone. Liquid and granular formulations must be watered in sufficiently to move insecticide off the surface, through thatch, and to the root zone. In lawns with heavy thatch it is of benefit to dethatch the lawn prior to insecticide application.
To control surface feeding pests, the target zone for the insecticide should be the leaves, stem and thatch. Spray formulations leave residues that remain on the surface and provide control of thatch inhabitants.
The objective of spray applications is to apply insecticides to the area where the target pest lives and eats. The volume of spray applied should be adequate for uniform coverage of leaves, stems and thatch. Too little volume will result in poor coverage and reduced control. In general, a minimum of 1 gallon of finished spray per 1000 sq. ft. is required for adequate coverage. Use coarse sprays to reduce drift and penetrate foliage.
Water and Irrigation Requirements
Quality and well as timing and quantity of water are additional factors involved in achieving adequate control of insects with insecticide applications. The pH of water used to mix insecticides should fall into the slightly acidic to neutral range. Water with a high pH (greater than 8) can cause rapid breakdown of some insecticides.
Timely use of irrigation can help get best results with insecticides for soil-inhabiting pests. During dry weather the turf should be irrigated prior to treatment. This will help the insecticide to penetrate grass blades and dry thatch. Follow label directions in regard to irrigation procedures following application.
Granular insecticides should be applied to dry turf. Granules will stick to wet grass blades and may not penetrate the thatch layer and reach the soil. Rapid watering-in is desirable with granular formulation, but it is not as critical as with liquid materials. At least one-half inch of water should be applied to activate granular materials and place it in contact with pests located at the surface. An additional half-inch to one inch of irrigation following treatment will carry the insecticide down through thatch and into the soil to the root zone. Delays in watering-in control materials will greatly reduce the chances of good control.
Bait formulations are used to attract soil-inhabiting pests to the turf surface where they consume a toxic dose of insecticide mixed in the bait. These materials will be ruined by rainfall or irrigation. Time of bait treatment is also critical. For night-feeding pests such as mole crickets and cutworms, baits should be applied late in the day.
Originally compiled from
- Beverly Sparks and Will Hudson. Insect pests of home lawns. Department of Entomology, UGA. Cooperative Extension Service Bulletin 1094. May, 1993.