Q: My grass looks yellow and is gradually disappearing in a ten foot square area. How can I tell if this is caused by insects or by disease?
A: Bugs in turf are very hard to find with the naked eye. Dr. Beverly Sparks, champion Extension Service bug-hunter, says you can try several methods to make them more visible.
DIG THEM OUT The Japanese beetles that ate our roses and plant leaves in June have pretty much disappeared. The females laid their eggs in lawns and then died. Now the eggs have hatched and the C-shaped white grubs have begun feeding on grass roots. If you had tremendous numbers of Japanese beetles this summer, yellow grass might be caused by grub damage. Slide a flat-bladed shovel two inches under a patch of grass and flip it up out of the ground. Examine the roots and soil for grubs. If you find more than eight per square foot, consider killing them with an insecticide labeled for use on grubs.
FLOAT THEM OUT If you have St. Augustine grass, chinch bug feeding on the grass blades could cause them to be yellow. A good way to check for chinch bugs is to perform a float test. Cut both ends from a gallon can and press one end firmly into the grass and soil. You might need to cut a circular slit through the turf first so the can sinks an inch into the soil. Fill the can with water and try to keep it full for five minutes. Any chinch bugs present will float to the surface. The adults are approximately one-fifth inch long and dark gray in color. Nymphs are smaller and reddish colored.
WASH THEM OUT Sod webworms chew at the base of grass plants and sometimes cause bare areas of turf. They hide in the thatch near the soil line when they are not eating. You can force them to reveal themselves by using a soapy water flush. Stir one-fourth cup of lemon-scented dish detergent into four gallons of water. Pour the mixture over an area of grass and watch what happens. Any insects present will wriggle themselves to the surface where you can identify them.
If you find an insect that you don’t recognize, any county Extension office can help you determine what it is and whether treatment is needed.