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Controlling chinch bugs on St. Augustine lawns

June 17, 2002|By Eric T. Natwick, Imperial County-University of California Cooperative Extension

St. Augustine grass is commonly used for lawns in Southern California and Arizona. One of the most serious insect pests on St. Augustine lawns is the southern chinch bug, Blissus insularis Berber.

Southern chinch bug adults are about .125 of an inch long, or about the size of a grain of rice. Adults are black with whitish wings that fold flat over their backs. There is a triangular black patch at the middle of the outer wing margins. Chinch bugs over-winter as adults and become active in the spring. Adult females lay 100 to 300 eggs in crevices of grass plants. The eggs change in color from pale yellow to red and hatch in about two weeks.

The immature chinch bugs, "nymphs," reach maturity in about a month. Young nymphs are yellow or red with a light-colored band across the back of the abdomen. Older nymphs are black with a white spot between the wing pads. Populations of chinch bugs build during the spring and summer, with several generations a year.


Chinch bugs are active from April through October, especially in full sun. Damage to lawns is due mainly to the feeding of chinch bug nymphs. They puncture the plant tissue with needle-like mouth parts and suck out the plant juice from nodes and crown of the turf grass. As a result, irregular patches of lawn turn yellowish, then brown and begin dying during hot weather. As the grass dies the chinch bugs move to the edge of the dead spots to feed. This causes dead areas to gradually enlarge. Chinch bug damage is usually greatest during hot, dry weather and in sunny areas rather than shade.

Natural enemies of chinch bugs include big-eyed bugs, ants and most importantly, the fungal insect pathogen Beauveria bassiana. Maintaining moist conditions favors development of Beauveria fungi that infect and kill chinch bug nymphs and adults.

Chinch bug can be controlled culturally by selecting a resistant variety such as Floralawn, Floratam or FX-10. Removal of thick thatch is important for eliminating conditions favorable for survival of chinch bug. Do not overfertilize. Applying too much nitrogen fertilizer increases chinch bug reproduction. Adequately irrigated lawns can better tolerate chinch bug feeding and promotes beneficial fungi that attach chinch bugs, such as Beauveria.

Lawns can be checked for the presence of chinch bugs by parting the grass in the yellow areas between dead and green grass. Watch for chinch bugs running close to the ground as they hurry out of the way.

Another method for checking is to cut both ends of a half- or 1-gallon can, push one end down into the yellowed grass and fill the can with water. If chinch bugs are present, they will float to the top.

A third way to detect a chinch bug infestation is the drench test. To perform a drench test mix 1 to 2 fluid ounces (2-4 tablespoons) of dishwashing liquid to a gallon of water. Two gallons may be required where soils are dry. Apply the solution to 1 square yard of lawn as evenly as possible using a sprinkling can. Be sure to test an area that includes both relatively healthy grass and adjoining unhealthy grass. The soapy water will cause insects to move to the surface. Identify and count the number of pest insects for a period of about 10 minutes.

You may consider treatments with an insecticide when 15 nymphs and adults per square foot are detected. Pyrethrum is a botanical insecticide from flowers of certain chrysanthemums and contains pyrethrins, naturally occurring insecticides that are toxic to insects. Most pyrethrum products include the synergist piperonyl butoxide. Pyrethrum may only temporarily paralyze the insects and pests may recover from effects unless piperonyl butoxide is added.

Use pesticides only according to the directions of the label. Follow all directions, precautions and restrictions listed. Do not use pesticides on plants that are not listed on the label.

Chinch bug treatments made in May reduce the first-generation nymph population. In most seasons damage appears first during dry periods in June as a result of the feeding of these first-generation nymphs. Damage may continue into the fall since there are several overlapping generations.

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