Chinch Bugs Hot and dry weather is ideal for pests like chinch bugs. A few small dead areas in the lawn can quickly spread, killing large sections that are costly to replace. If you have a St. Augustine lawn, you likely know that the southern chinch bug is a big problem. Most people tend to overlook them because they are so small. Adults are about 1/5 inch long and are black with white patches on the wings. The nymphs range from 1/20 inch long to nearly adult size. Small nymphs are reddish with a white band across the back, but become black in color as they grow. Chinch bug nymphs and adults can cause significant feeding damage. They remove plant fluids and inject a toxin that causes the grass to yellow, turn reddish brown and eventually die. Damaged areas often join together into large patches of dead, brown grass. These injured areas are more prone to injury because they are in hot spots along concrete or asphalt paved areas or in water-stressed areas where the grass is growing in full sun. The majority of damage occurs from April through September. Left untreated, these areas get bigger as chinch bugs span out in search of their next meal. The suggested economic threshold (the density of a pest at which a control treatment will provide an economic return) for the chinch bug is 15 to 20 insects per square foot. Though chinch bugs prefer St. Augustine grass, they will also feed on other grass species.