The Southern chinch bug, Blissus insularis, can be a significant insect pest in St. Augustine grass. Chinch bug infestations typically occur during hot, dry weather, sometimes causing their damage to be blamed on drought.
The first clue of chinch bug problems is irregular patches of brown, dead grass surrounded by a halo of yellowing, dying grass. This damage is often misdiagnosed as brown patch, a fungal disease that is common in
St. Augustine grass.
But there are key differences. Brown patch appears during periods of high relative humidity with daytime temperatures of 75 to 85 degrees and evening temperatures below 68 degrees. In addition, brown patch symptoms usually appear in circular or semicircular patterns, but chinch bug damage is irregularly shaped areas of grass.
Chinch bugs damage turf by puncturing plant tissue with needlelike mouthparts and sucking out sap. They feed on plants' crowns, stems and stolons. Their feeding causes yellow spots in the lawn that soon turn brown.
As the grass dies, the chinch bugs move to the edges to feed, so dead areas slowly enlarge. Although St. Augustine grass provides their favorite meal, occasionally they dine on Bermuda, zoysia and centipede grasses.
Investigate by looking for off-color areas, especially in direct sun, and near sidewalks and driveways. Populations of the bugs, which are 1/6 to 1/5 of an inch long, are concentrated near the soil surface.
To see them, part the grass at the edge of affected areas and examine the soil and base of the turf. With a heavy infestation, a few of these insects may walk on leaves or run on adjacent sidewalks.
Adults have black bodies and white wings with a distinctive triangular black mark. The nymphs or immature insects may be yellow or pinkish-red, with a light-colored band across their backs. As the chinch bug matures, it is brownish-black, with a white spot on its back.
Another easy way of finding these critters is by flushing them out. Cut out both ends of a 1-gallon can and push one end down into the affected grass at the edge of the yellowed area. Fill the can with water. Adult and nymph chinch bugs should float to the top within 10 minutes or so.
Chinch bug control starts with proper lawn care, including proper mowing, fertilization and irrigation.
High nitrogen levels and thick thatch layers in turf grasses invite chinch bugs. Thatch, the layer of dead roots and stems found between the green tops of grass and the soil, provides a protective home for chinch bugs.
Excessive application of nitrogen fertilizers produces rapid, succulent grass growth and can increase chinch bug population. A slow-release nitrogen fertilizer, which will produce steady, less succulent growth, is a better choice.
Other lawn-care tips: Don't over-water, don't over-fertilize and mow at the proper height to reduce thatch and discourage chinch bugs. To ensure a strong root system, St. Augustine grass should be kept 3 to 4 inches tall. Mow frequently enough that no more than a third of the leaf blade is removed at each mowing. Mowing with a sharpened blade also reduces stress on the grass.
Chinch bugs can be attacked by predatory insects, such as big-eyed bugs, minute pirate bugs and ants. Preserve beneficial insects by applying insecticides only after pests are positively identified.
Also, you should apply insecticides only when chinch bug populations and damage are significant. Then use the product at the recommended rate, read and follow label directions and practice safety precautions.
* Charla Anthony is the horticulture program assistant at Texas AgriLife Extension Service, Brazos County, 2619 Texas 21 W., Bryan, Texas 77803. Her e-mail address is