Is your St. Augustine lawn turning yellow lately? You might check your lawn for chinch bugs. Expanding, irregular patches of dead or stunted grass surrounded by a halo of yellowing, dying grass often provides the first clues of the presence of chinch bugs.
Chinch bug damage usually occurs in sunny locations during hot, dry weather. Chinch bug damage can sometimes be confused with certain lawn diseases or other physiological disorders as well. For example, brown patch is a common disease in St. Augustine. Brown patch symptoms usually occur in a circular or semi-circular pattern as opposed to the irregular shaped areas of chinch bug damage. Chinch bug damage can also resemble drought stress. Detecting the actual insect is the best proof of chinch bug damage. In some instances, chinch bugs and disease of lawns can be present at the same time.
Adult chinch bugs are small, slender insects measuring one sixth to one-fifth of an inch long. They have black bodies with white wings, each of which bears a distinctive triangular black mark. Recently hatched nymphs are wingless, yellow or pinkish-red with a light-colored band across their backs (abdomen).
Adult chinch bugs are inactive during winter months. Reproduction occurs in warmer weather with the female laying up to 300 eggs, which can hatch in approximately two weeks. The nymph stage lasts less than 30 days during warmer weather. The entire life cycle of a chinch bug lasts seven to eight weeks.
Managing this pest begins with proper lawn care. Keep the thatch layer to a minimum. Thatch is the layer of dead plant material found between the green tops of the grass and the soil below. Thatch can provide a protective home for the chinch bugs, and it makes chemical controls less effective. Too little or too much water on the lawn can lead to chinch bug problems. Chinch bugs prefer hot, dry environments. Frequent watering also promotes shallow root systems in St. Augustine, making it more susceptible to injury by chinch bugs.
Damage normally appears when there are approximately 20 to 25 chinch bugs per square foot. Homeowners can perform a test to determine chinch bug presence in the lawn. One recommendation is to take a coffee can and remove the bottom and top lids, being careful of any metal lids and sharp edges. Take this can and push it into the soil using a twisting motion in the area you suspect chinch bug damage. Fill the can with water for about 10 minutes and check for chinch bugs as they will float to the surface if present. For a 4-inch diameter can, damaging numbers of chinch bugs present are more than two bugs per sample. For a 6-inch diameter can, an average of four to five chinch bugs or more per sample indicate damaging numbers. Several samples from different locations should be taken in the damaged grass.
Biological controls for chinch bugs include other insects such as the big-eyed bugs, minute pirate bugs, spiders, wasps and ants. Repeated applications of insecticides can reduce these beneficial insect numbers. Use insecticides only when necessary. Big-eyed bugs are often mistaken for chinch bugs. They are similar in size to chinch bugs. Big-eyed bugs have large protruding eyes and a head at least as wide as the thorax. Big-eyed bugs also lack the chinch bug’s distinctive white wings with black triangular markings. Chinch bugs have smaller heads and eyes with a more slender body.
Insecticides labeled for chinch bugs contain active ingredients such as carbaryl, bifenthrin, cyfluthrin, lambda-cyhalothrin and permethrin. Be sure to read and follow all label recommendations when applying insecticides. Good cultural practices including water, fertility management, and thatch control can dramatically reduce the need for insecticides to control chinch bugs.