Mullis: Check, treat for chinch bugs at first sign of damage to St. Augustine lawns

It’s time for my annual warning about chinch bugs for those of you who have St. Augustine lawns.


I began scouting my own backyard several weeks ago in the small area where they always show up first. About the first of June I found them crawling around and causing some minor damage. I treated just that small area a couple of days later.

Many people have St. Augustine grass in shady areas because it is our most shade tolerant grass. In these areas, you don’t have to worry about chinch bugs. They like open sunny (hot) areas of the lawn. Prominent places are near driveways and sidewalks. I have seen yards where you could almost draw a dividing line from where it went from sun to shade with chinch bugs causing damage in the sunny part and stopping once you get to the shady part.

The first sign of chinch bug damage to a St. Augustine lawn is the grass will look wilted even though you have recently watered it or it has rained. From this wilting stage it will progress to turning yellow, then eventually turning straw-colored brown. If it reaches this point it is dead.

If you have one, two, or even three of the other grasses mixed in with your St. Augustine and notice only the St. Augustine looking bad or dying, suspect chinch bugs.

It can be somewhat confusing in knowing what you are looking for because chinch bugs look a little different depending on their life cycle. The adults are black and about 1/6-inch long. The wings are folded over the back forming a white or silver cross-shaped mark. The white markings will look a little different depending on the life stage. There will usually be other black or brown bugs crawling around, but they are solid black or brown and are harmless to the grass.

Young chinch bug nymphs are about the size of a pin head, red to orange in color with a white band across their back. The full grown nymph (just before the adult stage) is black and has a white spot on the back between the wing pads. Like most insects, the nymphs actually do more damage than the adults.

Chinch bugs are fairly quick and hard to catch. Search in the wilted grass at the edge of a dead patch. Part the grass and pull back the thatch down to the soil. In thin areas of grass you might even find them crawling across the top. If you do not see the chinch bugs, pull up a handful of grass including the thatch and runners. Lay it on a table or put it in a plastic bag and see if chinch bugs crawl out. Next, gently pull off the leaves to see whether the bugs are hiding where the grass blades come together at the base of the plant.

If you are seeing them or the chinch bugs are only causing damage in a small part of the yard, just apply spot treatments with granular or liquid insecticides, especially this early in the season. This will allow for the conservation of natural enemies, as native parasites can play a significant role in chinch bug management. This is why scouting is so important.

Synthetic pyrethroid insecticides are effective in control of chinch bugs, but they don’t provide residual control. You can use any of the synthetic pyrethroid insecticides (that end in “thrin.”) Bifenthrin (Ortho Max Bug-B- Gon, Over ‘n Out & Hi-Yield Bug Blaster), cyfluthrin (Bayer Advanced) and lamda-cyhalothrin (Spectracide) are all good ones. The Bayer Product Complete Insect Killer has a combination of b-cyfluthrin and imidacloprid so it provides a longer residual control. You can also apply Sevin but it does not work that well.

In most cases, irrigate the grass area several hours to a day before the insecticide application unless noted otherwise on the product label. Granules can be used but they must be watered in thoroughly. When spraying an insecticide, it is very important to use lots of water (4 to 5 gallons per 1,000 square feet) to get the chemical down to the insects.

The following cultural practices can help in chinch bug control. Use little nitrogen during the hot summer months and use slow release fertilizers. Overfertilization with nitrogen can make chinch bugs worse. Water deeply about once or twice per week applying three quarters to one inch of water each time. Water between midnight and 10 a.m.

If the thatch layer is thicker than one inch dethatch the lawn as soon as possible. Topdressing is the best way to dethatch a St. Augustine lawn in order to prevent damage to the grass from a dethatching machine.

Chinch bugs, like many insects, have multiple generations per season, so if you don’t get them all, the populations will build back up. This is what we have to guard against when dealing with chinch bugs.

Chinch bug problems are very much determined by the weather. If we continue to get a lot of timely rain the rest of the summer and early fall, they won’t be much of a factor but if it turns hot and dry, even for short stretches of time, watch out!

Chinch bugs can kill a lawn quickly, so if you are seeing problems, don’t delay in scouting and/or treating your lawn.