Does your lawn have the St. Augustine blues?

By Staff
July 11, 2004
During summer, many gardeners complain about dead spots in St. Augustine lawns. The first step toward determining treatment is deciding if the problem is caused by cultural stress, such as fertilizer burn, or by disease or insect pests.
Since you can't ask the grass what's wrong, gardeners are often forced to become detectives.
The first step in the detective game is to determine whether any accidents or changes in lawn culture have occurred within the past few months.
Spilled chemicals, such as gasoline or fertilizer, can cause grass to die in spots. Mounds of leaves or thick piles of grass clippings left over winter can smother the turf and kill plants. High spots in the lawn may be dead because of continual scalping by the mower.
If the dead grass is in a low area, seasonal standing water could have killed the plants. We've had so much rain that it's a great time to identify your low spots. Put on some rubber boots and get your umbrella during or right after a rain. Go outside and make note of any areas of standing water. Later when the weather clears, top dress the low areas with sand so water will run off instead of accumulating.
If bare areas are under trees, the shade may have become too dense. St. Augustine is more shade-tolerant than other southern grasses, but will not tolerate heavy shade.
Grass diseases
If you can discover no cultural reason for the problem, check for diseases by examining individual grass plants around the edges of the dead spot for leaf spots and water-soaked lesions.
Two diseases of St. Augustine prevalent during wet weather are brown patch and gray leaf spot.
Brown patch is the most common disease of St. Augustine. The fungus causing brown patch attacks leaves and stems. Grass dies in large irregular circles that can be several feet in diameter. The plants along the edge of the circle appear water-soaked.
Gray leaf spot causes grass blades to develop tan spots with dark margins. Infested lawn areas appear scorched. Brown patch can devastate an entire lawn, but gray leaf spot rarely kills the whole area.
This summer, we've had perfect weather for both those diseases. Keeping dead grass or thatch from accumulating in the root zone and avoiding overfertilization with nitrogen will aid in prevention.
What about bugs?
If your lawn has passed the disease check, you should examine the turf for chinch bugs.
Chinch bugs attack the leaves on patches of grass growing in the sun. The plants take on a yellowish wilted appearance when the chinch bug sucks the plant's juices and injects a poison into the leaves. Homeowners usually do not notice the damage until yellowish-brown or dead patches appear in the lawn.
Chinch bugs are small about 1⁄5 of an inch long with black, white and sometimes red coloration. If you suspect chinch bugs, sink a bottomless can into the edge of a damaged spot, fill the can with water and wait about 5 minutes to see if any chinch bugs float to the surface.
Good news for the Meridian area is that chinch bug damage is rare during wet summers. Chinch bug infestations are more likely in hot dry weather during late summer and fall.
What to do about it
In your search for clues, remember that while summer rains continue, disease damage will be more likely than chinch bug damage.
If you diagnose your problem as pest damage, your nurseryman can verify your diagnosis and recommend treatment.
After the treatment, you should pamper your lawn for the rest of this season and watch for symptoms again next year.
Gail Barton is coordinator of the Horticulture Technology Program at Meridian Community College.