Invasion of the Chinch Bugs

With its lush wide blades and dark green color, St. Augustine (or Charleston) grass is one of the most popular lawn grasses in Augusta. It is the most shade tolerant variety of grass that will also grow in full sun, making it a very versatile choice for area lawns. If you have St. Augustine growing in full sun, however, you need to be aware of a big problem that can be caused by small, but destructive chinch bugs. Fortunately they are mostly a problem for St. Augustine, as the other three lawn grasses grown in Augusta are not usually affected.

Chinch bugs thrive in hot dry weather, primarily April through October. And the window of infestation has steadily increased over time as seasons of high temperatures have increased.

When we have a summer with temperatures in the low 90s and average rainfall, chinch bugs aren’t a problem. Cool, cloudy and rainy weather promotes fungal pathogens that attack chinch bugs and keep populations low. But dry, extremely hot summers like the ones we’ve experienced the past couple of years create idyllic conditions for the troublesome pests.

Symptoms

Chinch bugs only attack grass growing in sunny areas. They will not touch shady areas. This is so much the case that you can see the patterns of destruction that precisely align with the sunny spots in a lawn. So be on the lookout for damage in sunny areas especially near sidewalks, driveways and streets since these areas radiate the most heat.

The first sign of chinch bug damage is grass that looks wilted even after recent watering or rain. If your grass looks wilted on the same day you’ve watered it or the very next day, it’s a safe bet you have chinch bugs. During the next and final stage your grass will begin to turn yellow and eventually straw-colored brown. Once the affected area reaches that point, it is dead.

In the initial phase of damage, chinch bugs are often mistaken for drought stress because of the wilted appearance. There are also some diseases that mimic chinch bug damage such as take-all patch, which also commonly affects St. Augustine. In that case the grass will sometimes turn yellow and die out; however, it usually forms a circular or semi-circular pattern, as opposed to the irregular shaped patterns in the sunny areas of your yard.

Confirming the Diagnosis

There are a variety of ways to determine whether or not your lawn has chinch bugs. The easiest and fastest way is to part the grass in or near the yellowed areas and pull back the thatch down to the soil and look for them. In thin areas of grass or during heavy infestations, you may even find them crawling across the top of the grass. Do your search on a warm sunny day during the middle of the afternoon. If you are still uncertain, place a large square of turf in a large, sealable plastic bag. Seal it and place it in the sun. After several minutes, as the bag heats, insects will begin to collect on the inside of the bag.

You can also mix one fluid ounce of dishwashing liquid in two gallons of water and drench four square feet of the solution at the edge of the affected area. If chinch bugs are present, they will emerge at the grass surface in about two minutes.

Another common method is the flotation technique. A coffee can or similar sized can, with the ends cut out, is pushed two to three inches down into the turf at the edge of a suspected area of chinch bug infestation. Do this test on a wilted or yellowed area of the lawn as the bugs in the brown areas will have moved on to healthy grass. Keep the can filled with water at least above the grass surface and wait about five minutes. If chinch bugs are present, they will float to the top. Repeat this monitoring technique in several spots at the edge of suspected areas.

Treatments

There are several ways to control chinch bugs,  including cultural, biological and chemical control.Cultural methods involve preventive steps to discourage infestation in the first place. Rapid lawn growth due to over-fertilization with nitrogen can increase chinch bug survival, shorten development time and increase the number of eggs that are laid. So it is helpful to use smaller amounts of nitrogen during hot summers and use slow-release forms.

Excessive thatch is another contributor to chinch bugs. Over-watering and over-fertilizing contribute to thatch buildup. Too much thatch can keep pesticides from reaching the soil level and killing the bugs. Thatch can be mechanically removed by an aerator or by topdressing the lawn with topsoil. The soil has microorganisms that break down the thatch layer. Since dethatching machines are so destructive to St. Augustine, topdressing is the preferred method.

Water your grass deeply about once or twice per week  in the absence of rain, applying three-quarters to one inch of water each time, wetting the soil approximately six to eight inches deep. Be sure to let it dry out between irrigations. To check the amount of water you are applying, place several open containers on the lawn while the sprinklers are running. Then check the soil with a spade or shovel to see how deep it has soaked into the ground, which will let you know about how long you need to water. Irrigate between midnight and 10 a.m. for the most efficient use of the water.

Chinch bugs have many predators, including big-eyed bugs, minute pirate bugs, spiders, wasps and ants. The most important of these are big-eyed bugs, which are often mistaken for chinch bugs. If chinch bugs are causing damage in only a small part of the yard, apply spot treatments of an insecticide so that you won’t also kill their natural enemies.

There is no silver bullet pesticide to control chinch bugs. Synthetic pyrethroid insecticides will effectively control chinch bugs, but they don’t have long residual control and there is evidence of resistance to this family of insecticides. All of the synthetic pyrethroid insecticides end in “thrin.” The ones you will find in garden centers are bifenthrin (Ortho Max Bug-B-Gon, Over ‘n Out and Hi-Yield Bug Blaster), cyfluthrin (Bayer Advanced), lamda-cyhalothrin (Spectracide) and permethrin (Green Light and Spectracide). The Bayer Product Complete Insect Killer has a combination of b-cyfluthrin and imidacloprid so it provides a longer residual control. 

All of these products are available in granular and liquid concentrates. Apply the granular variety with a standard fertilizer spreader and irrigate lightly to activate the insecticide.

Liquid sprays are usually applied with a hose-end sprayer or hose-end applicator that can apply 15 to 20 gallons of water per 1,000 square feet. To ensure even coverage, spray back and forth across the same area. Use a surfactant or a small amount of dishwashing liquid in your liquid spray solution because it will enhance control, especially in turf with heavy thatch.

If chinch bug density has decreased by at least 80 percent, then the treatment is considered successful. A retreatment may be needed if the eggs hatch, if encroachment occurs from a neighboring lawn or if the insecticide residue breaks down. Avoid using insecticides that are not specifically for use on turfgrass or for controlling turf-feeding insects.

Chinch bugs develop resistance to insecticides if only one type of product is used continuously, so if you have to treat the lawn more than once, change to a different insecticide.

Unfortunately, all of the St. Augustine varieties grown in Augusta are highly susceptible to chinch bugs. There are no commercially available chinch bug resistant varieties of this grass. If and when they ever develop one, I am sure it will take our area by storm