If you notice brown patches appearing on the lawn, and the kids are complaining of dry crunchy grass, you most likely have chinch bugs (Blissus spp.) sucking the life from your lawn. Adult chinch bugs lay eggs among the grass roots where they chew on the roots; adults also damage grass by sucking sap out of the stems. Your grass can withstand this damage with proper care and grow back, except in areas that suffer heavy damage from the pests.
Chinch bug grubs curl up in a C-shape under the soil when exposed. Adults have black bodies with white wings that fold over their backs. Nymphs are reddish, pink or orange with white bands. Pests feed on grass during mid-summer through fall and are especially troublesome for St. Augustine grass (Stenotaphrum secundatum), a warm-season grass that thrives in U.S. Department of Agriculture plant hardiness zones 8 through 10.
Damage and Light Infestations
Chinch bug damage begins as yellow spots in the lawn that quickly turn a rusty, reddish brown before dying. The damage is often confused with drought stress; however, the turf does not improve, even with supplemental irrigation. With proper treatment, grass will grow back, but how quickly is dependent upon the extent of damage. Small patches that were treated right away often fill back in during one growing season, while larger patches that sustained more damage may take up to a year or more for the lawn to recover.
While damage caused by chinch bugs in small populations can recover fairly quickly with proper irritation and fertilization, heavy infestations can cause irreversible damage. Chinch bugs inject toxic substances while feeding on plant juices, and the toxic effect of this saliva in large populations often kills grass by preventing proper water uptake. After heavy damage, you can reseed, resod or use plugs in the damaged area of the yard.
Cultural controls for chinch bugs include controlling thatch and keeping the lawn moist to promote beneficial bacteria that attack the pests. Proper mowing also helps lawns withstand an infestation. Chemical treatments generally include a insecticide product containing pyrethroids; however, in some areas cinch bugs are resistant to this product. An alternative is a granule insecticide that contains clothianidin. One 12-pound bag of granules covers a 4,000-square-foot area. Apply the product using a drop or rotary spreader, and water thoroughly after applying.