Richard C. Bogren, Kirk-Ballard, Heather
LSU AgCenter Horticulturist
(08/16/19) We are continuing to experience a heat wave this August without much relief. One thing that thrives in the hot and dry climate in our lawns and can become a real issue this time of year is chinch bugs. They are especially fond of St. Augustine grass.
Chinch bug damage can be easily mistaken for lack of water and overall heat-stressed turf. The lawn will look like it has not been watered because of the curling and shriveling up of the grass blades that eventually turn brown and die. However, it can also be a sign of chinch bug damage.
You’ve got to do some investigating to get to the root of the problem.
One key sign of chinch bugs is that the symptoms first appear as patches of dead grass in areas where heat is radiated from storm drains near streets and around sidewalks and driveways. This often misleads folks into believing it is caused by drought.
Another definitive clue that you may have chinch bug problems is that the damage does not occur in circular patterns like many of the fungal turf diseases. The brown spots will be more random, and the grass will have jagged edges that will turn yellow before fully dying and going brown.
So what exactly is a chinch bug? It is a slender, black insect that is about 1/8 inch long when fully grown. It has white wings that are marked with a triangular black patch in the middle. The immature insects hatch from eggs and are red and a band of white across the back juts out behind the pads where the adult wings will later develop.
Chinch bugs do their damage with a piercing-sucking mouthpart by inserting a slender beak into the grass at the base of the plant. It then injects a toxin and extracts the plant juices. This toxin can be quite damaging, and the grass cannot recover. If you do not stop chinch bug activity quickly, they can spread into new turf, causing large areas of damage.
Chinch bugs reproduce quickly, as the female deposits 15 to 20 eggs per day for 20 to 30 days on a blade of grass. The eggs hatch in seven to 10 days.
These insects are rather difficult to detect because they so tiny and often are not readily visible in the lawn from our viewpoint looking down. If you suspect chinch bugs are to blame for the damage in your lawn, try confirming this suspicion by using a lemon-scented soap mixed in water and poured on the brown area.
To make the solution, add 1 to 2 tablespoons of lemon-scented dish soap to a gallon of water. After pouring the solution over a small area, wait for five minutes. If chinch bugs are present you, will see them climbing up the grass blades. To really investigate, you may need to get down on your knees and look around in the thatch.
You can also take a plug of grass from the damaged area and dip it into the soapy water. Then watch for bugs floating to the surface of the solution.
Thatch is the area where the lawn sloughs-off old stems and roots and replaces them with new plant parts. The accumulation of plant parts often exceeds the rate at which the material breaks down. This creates a layer of thatch above the soil surface. A small amount of thatch is beneficial because it provides organic matter and can help reduce water loss from the soil. However, heavy thatch of more than 3/4 inch deep can be a place where insects such as cinch bugs will thrive.
Late summer is a good time to dethatch your lawn. Dethatching will increase the infiltration of air, water and nutrients into the soil and down to the grass roots while also stimulating new growth. By increasing lawn vigor, you remove a favorable environment for cinch bugs and other insects to infect your lawn.
Dethatching is done in one of two ways. One is by using a thatch rake or heavy garden rake with thick tines to rake deep down into the grass to remove the thatch. Raking is best for an area that is not heavily thatched. If the thatch is thick and soil compaction is also an issue, mechanical core aeration is better. Aerators are implements that remove cores, or plugs, from the sod. Rental equipment is often available, and many local landscape and turf companies offer this service.
Once you have positively identified chinch bugs are the culprit, they can be controlled by spraying with insecticides containing one or more of the active ingredients Scimitar CS, carbaryl or cyfluthrin/imidacloprid according to the label directions.
The pH of the water used to create the spray solution is important. If the pH is too alkaline, it can cause the insecticide to break down before it has a chance to work, making it less effective and causing you to apply more. Check the pH of the water with pH paper or meters that can be readily found at most garden stores and nurseries. The pH should be 5.5 to 6.5. You can buffer the pH down by adding vinegar to the water and rechecking as necessary until you’ve reached the desired pH.
Retreating again in two weeks to kill any hatched eggs is best practice. If you see further activity two weeks later, a subsequent insecticide application may be necessary.
A chinch bug has white wings that are marked with a triangular black patch in the middle. Photo by Ron Strahan/LSU AgCenter
About 1/8 inch long when fully grown, chinch bugs can severely damage lawns, particularly St. Augustine grass. Photo by Ron Strahan/LSU AgCenter
Chinch bug damage on a lawn appears as large patches of dead grass. AgCenter file photo by Dan Gill