Brown St. Augustine in summer: drought or chinch bugs?

Signs your grass just needs water

Texas A&M AgriLife says to water a St. Augustine lawn right away when you see these signs:

• The edges of the blades start to curl.
• The grass doesn't spring back quickly after you walk on it.
• The lawn takes on a dull bluish-gray color.

Even on one SAWS watering day a week, watering with a hand-held hose is allowed any day. See SAWS watering rules.

What chinch bug damage looks like

The southern chinch bug is one of the most important insect pests of St. Augustine grass in Texas, and it does the most damage in the southern half of the state. AgriLife describes the damage like this:

• Patches of dead or stunted grass with a halo of yellowing, dying grass around them.
• The patches are irregular and grow and merge as the bugs multiply.
• Damage can spread fast in sunny spots during hot, dry weather.

Look first at off-color areas in direct sun and along sidewalks and driveways.

What the bugs look like

Adults are tiny, about 1/6 to 1/5 of an inch long, with black bodies and white wings that each have a black triangle mark. Young ones (nymphs) are wingless and yellow or pinkish-red with a light band across the back.

Don't confuse them with big-eyed bugs. Those are about the same size but have large, bulging eyes and a wide head, and they're beneficial: they eat chinch bugs.

The coffee-can test

This test comes from the AgriLife fact sheet:

1. Take a coffee can and remove the top and the bottom.
2. Twist it into the ground at the edge of the damaged area, where the grass is yellowing but not dead yet. Cut the grass around the rim with a knife if you need to.
3. Fill the can with water and wait about 10 minutes.
4. Count the chinch bugs that float up.

With a 4-inch can, an average of more than 2 bugs per sample means damaging numbers. With a 6-inch can, it's 4 to 5 or more. Test several spots. If you find few or no chinch bugs, the cause is probably something else, like lack of water, white grubs or a disease.

What about brown patch?

Brown patch is a common disease of St. Augustine leaf blades. According to AgriLife, its spots are usually circular or half-circle shaped, while chinch bug damage is irregular.

How to prevent chinch bugs

AgriLife says good lawn care is where control starts:

• Water deep, not often. Wet the soil about 6 inches deep and let it dry between waterings. Drought-stressed lawns are more likely to be damaged, and frequent watering keeps roots shallow.
• Mow regularly. Don't cut more than 35 to 40 percent of the blade at once, which usually means mowing at least once a week while the grass is growing. AgriLife Extension in Bexar County recommends 3 inches for St. Augustine and 4 inches in summer.
• Don't overdo fertilizer. Too much makes the grass more attractive to chinch bugs. AgriLife's limit for St. Augustine is 3 to 4 pounds of nitrogen per 1,000 square feet a year in sun and 2 in shade.
• Keep thatch thin. The layer of dead material between the grass and the soil protects the bugs. Over 1 inch, it may need to be removed.

There's no chinch bug-resistant St. Augustine to fall back on: AgriLife says common varieties like Raleigh are highly susceptible, and Floratam no longer appears to be resistant.

If you need to treat

AgriLife recommends insecticides only when you find chinch bugs in damaging numbers, treating the affected area and around it, and always following the label.