I have been getting calls from all over the Acadiana area regarding this problem. I am seeing sod webworms and to a lesser extent armyworms in the same yards. At least every other St. Augustinegrass yard has some degree of damage. These two moth larvae together have caused more damage than I have ever seen in home lawns.
Tropical sod webworms are one of the most destructive pests of St. Augustinegrass and carpetgrass. Just drive around and look at all the damage.
So far centipedegrass and bermudagrass and zoysiagrass have been less affected. In fact, I have seen St. Augustinegrass completely devastated, growing next to zoysiagrass that was totally unaffected. The damage looks unusual and shocks the homeowner, because it appears to happen overnight.
The lawns may have a few chewed up circular areas or browned out areas that exceed a 1,000 ft. area. At first glance, you will think it’s a disease. However, after close inspection of the turf, you will see that the leaves have heavy chewing damage.
Young larvae feed along the mid-rib trough of the leaf. Mid-sized larvae chew notches in the edges of leaves and older larvae will completely strip off the leaves, similar to the damage caused by armyworms. It is the notched edges on grass blades that are the tipoff. Additionally, the worms leave trails of a silky web as they crawl through the grass. You can spot these “webs” in the morning when dew is on the ground. Like armyworms, watch for birds feeding in the area.
Armyworms feed at midday, but sod webworms prefer to feed at night. I have found that just looking care-fully through the grass during midday may not turn up any webworms. However, if you make up a soapy solution in a couple of gallons of water and pour it in a transition area (damaged turf transitioning to good turf), the armyworms present in the area will go crazy. Tropical sod webworms will at least start moving, making them easier to spot.
Moths are 0.5 to 0.75 inches long, and have snout-like projections on their heads. You see the moths fluttering over the turf and in flowerbed areas nearby.
This short-lived moth does not feed on the turf, but is responsible for laying the eggs in the grass. The eggs hatch in seven to 10 days and the larvae begin feeding on the turf. The larvae (worms) can get up to one inch long and are light green to gray green, with dark spots on their body. There is no characteristic inverted “Y” shape on the head of webworms like you see with armyworms. The tropical sod webworm completes their development from egg to moth emergence in five to six weeks. The species overwinters as larvae in the soil. We could get three to four generations in one season.
The good news is that control is possible, and the same insecticides that kill armyworms work well on tropical sod webworms.
The combination of worm damage, hot temperatures, and drought may kill off lawns that were already weakened by cold damage, disease, low mowing, and overall low fertility. However, it is likely for lawns that were in good shape prior to the worm damage, to recover once the worms have been killed.
(For more information, contact Dr. Chris Robichaux, county agent/area horticulturist, St. Martin/Iberia Parishes, at 332-2181 or 369-4440.)