Across the state, lawns are in trouble.
Sod webworms are the main culprit this year, said LSU AgCenter Extension specialist Ron Strahan.
“The numbers are biblical," Strahan said. "We have observed nearly every house on a single street with damage in the lawn.”
The first sign that your lawn might have a problem are small moths that are light brown to dark brown with striping on the wings. They fly around as you walk through the grass or around outdoor lights at night. These moths lay eggs on grass blades.
Larvae hatch a week or so later, maturing into adult moths in three to five weeks. There can be two or more generations each year.
Louisiana lawns are experiencing a devastating loss of #turfgrass this year due to the tropical sod webworms. LSU AgCenter horticulturist Heather Kirk-Ballard discusses identification and control methods. pic.twitter.com/reafWF1965— LSU AgCenter (@LSUAgCenter) September 30, 2020
Larvae are amber in color but become greener as they feed on the blades of grass at night, causing damage to the lawn.
Another sign of sod webworms are yellowing and browning patches of dead lawn. Look at individual grass blades for a chewed appearance, with pieces of missing or chunks bitten out. The caterpillars are making a feast of your lawn.
Worm castings (caterpillar poop) in the ground are another clue. The castings, which are digested grass, appear as light beige pellets at the base of the plants just above the soil level.
In the early morning, when the dew is still on the ground, water droplets from the dew will be trapped in the webbing, and this is where sod webworms get their name. If you dig thoroughly in the soil, you can usually find a tiny caterpillar about ½- to 1-inch long.
Sod webworms seem to especially love St. Augustine grass.
If you see birds going into a feeding frenzy, pecking around in the grass, that's usually an indicator sod webworm caterpillars are there.
Heavy infestations can lead to stress, causing your lawn to be more susceptible to fungal diseases such as gray leaf spot and to other insects such as chinch bugs and armyworms. A combination of these problems can lead to the death of turfgrass.
To help control sod webworms, use an insecticide with the active ingredient bifenthrin.
LSU AgCenter entomologist Sebe Brown recommends liquid rather than granular applications for better control. You will need to retreat the lawn again in seven days to kill any newly hatched eggs. Spray will not control the moths. It is most effective on the main culprit doing the damage — the caterpillar.
Treat the infested areas and extend 3 to 4 feet past where you see browning. Moths will continue to lay eggs, so continue to monitor the lawn. Eggs hatch every seven days.
The cooler weather of fall will slow down the generation interval but not kill the worms already in the lawn. Last year’s mild and short winter is likely the cause of the large populations this summer.
The good news is that in most cases your grass will recover. Water your lawn during extended periods of drought that are especially common in October here to help the grass recover before going into winter dormancy.
It’s also time to stop fertilizing the lawn and wait until spring to apply any new applications.