There’s an irregular-shaped patch of dead grass in the middle of the lawn and it is getting bigger by the week. What is causing this? If this is a St. Augustine lawn, chinch bugs may be the culprits. Chinch bugs are the most important insect pests of St. Augustine grass, but don’t start treating until you are sure chinch bugs really are the cause of the problem. There are several diseases that cause similar symptoms, and insecticide treatments will not control disease problems.
Check for chinch bugs by using your fingers to dig through leaves, stems, and thatch at the edge of the dying grass—where the grass is still green or just beginning to yellow. Better yet, take a one-gallon metal can that has had the bottom cut out, force it into the turf, fill it with water, and check for floating chinch bugs. It takes around 20 chinch bugs per square foot to kill grass, so chinch bugs should be relatively easy to find if they are the cause of the problem. Chinch bug outbreaks are more likely during periods of hot, dry weather, and grass growing in full sun is more susceptible than grass that receives some shade. This photo shows a single adult chinch bug (about 1/8 to 3/16 inch long) a couple of dark-colored older nymphs, and several of the younger, red-colored nymphs.
Control: Water turf well before treating; this forces the bugs to move closer to the surface where the insecticide can reach them more readily. Then spray with a lawn insecticide containing an active ingredient such as bifenthrin, cyfluthrin, lambda-cyhalothrin, or permethrin using a hose-end sprayer to apply 15 to 20 gallons of finished spray per 1000 square feet. If you must use lower volumes of spray, water lightly after treatment, no more than 1/8 to ¼ inch, to wash the spray into the thatch area where the chinch bugs are most active. Don’t water too heavily or you will wash the insecticide past the bugs. For best control of heavy infestations, apply a second treatment two weeks later. Granular insecticides can also be used to control chinch bugs, but be sure to water in according to label directions. Products that contain clothianidin will control chinch bugs that are resistant to the pyrethroid insecticides listed above.
See page 6 of Extension Publication 2331, Control Insect Pests In and Around the Home Lawn for more information: http://extension.msstate.edu/sites/default/files/publications/publications/p2331_0.pdf
For information on chinch bug control in commercial turf see pages 5 and 6 of Extension Publication 1858, Insect Control in Commercial Turf: http://extension.msstate.edu/sites/default/files/publications/publications/p1858_1.pdf
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service. The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.