St. Augustine grass is a popular choice for warm-season lawns across the southern United States. Its vigorous growth creates a thick thatch layer that can shield pests, making detection difficult until an infestation is well-established. Maintaining a healthy lawn requires vigilance against these insect invaders. Early identification of the damage caused by these pests is important for successful management before significant turf loss occurs.
Identifying and Managing Southern Chinch Bugs
The southern chinch bug is the most damaging insect pest of St. Augustine grass, causing extensive turf loss in hot, sunny areas. Adult chinch bugs are tiny, measuring about one-fifth of an inch long, with black bodies and white wings marked by a distinctive black triangle. They use piercing-sucking mouthparts to extract plant fluids from the base of the grass near the soil line.
As chinch bugs feed, they inject a toxic substance that disrupts water movement, causing the grass to turn yellow, then reddish-brown, and eventually die. This damage initially appears as expanding, irregular patches of dead turf. These patches are often mistakenly attributed to drought stress or a fungal disease, but they typically present in non-uniform shapes that spread outward from a central point.
To confirm their presence, homeowners can use the “float test” by cutting both ends from a coffee can or PVC pipe and pressing it into the soil at the edge of a damaged area. Filling this cylinder with water will force the insects to float to the surface within a few minutes. An application of insecticide is warranted if more than three chinch bugs are found per sample area.
Management often requires liquid or granular insecticides, but resistance is a growing concern. Rotating between different chemical active ingredients is necessary to prevent resistance development in the chinch bug population. Treatment should focus on the edge of the damaged area where the active bugs are located, avoiding the center where the grass is already dead. Watering lightly before application helps the insecticide penetrate the dense thatch layer where the chinch bugs reside.
Identifying and Managing Sod Webworms
Sod webworms are the larval stage of small, tan-colored moths. The larvae are grayish-green caterpillars, reaching about three-quarters of an inch in length, and are identified by numerous dark spots along their bodies. These caterpillars are night feeders, chewing grass blades near the soil surface. During the day, they retreat into silk-lined tunnels in the thatch layer.
Damage from webworms appears as small, ragged patches of grass where the blades look notched or clipped. As the infestation progresses, these patches merge into larger, straw-colored areas, creating a scalped appearance. A key sign is the presence of small, bright green fecal pellets, known as frass, which can be found in the thatch near the soil surface.
A soap flush test can confirm an infestation by irritating the larvae and forcing them to the surface. Management strategies must target the larval stage during their active feeding time. Applying contact insecticides in the late afternoon or early evening is most effective. Biological controls, like the bacterium Bacillus thuringiensis (Bt), are also effective as they must be ingested by the caterpillar to be lethal. Repeat applications are often necessary to break the webworm’s life cycle since the initial treatment does not kill the eggs.
Identifying and Managing Mole Crickets
Mole crickets cause damage to St. Augustine grass through feeding on roots and shoots, and mechanical disruption. The primary visible damage comes from their aggressive tunneling just beneath the turf surface. These tunnels create raised, meandering ridges that disrupt the root system.
The tunneling causes the turf to lift and feel spongy underfoot. The uprooted grass desiccates quickly, leading to irregular dead patches, especially in late summer and fall. Confirmation of mole crickets can be done with the soap flush test, which forces them to emerge from the soil.
Effective chemical control depends on timing, focusing on the small, susceptible nymphs that hatch in early summer (mid-June to July). Treating adult crickets later in the season is significantly less effective. Insecticide products, whether granular or bait formulations, should be applied in the late afternoon or evening when the crickets are most active near the surface. Granular insecticides should be watered in lightly to move the chemical into the root zone, while baits must be applied to a dry surface.
Cultural Practices for Long-Term Prevention
Reducing reliance on chemical treatments requires implementing cultural practices that promote a resilient lawn environment. Proper mowing is a simple yet effective preventative measure, as St. Augustine grass should be maintained at a height between 2.5 and 4 inches. Keeping the grass taller encourages a deeper, stronger root system that is more tolerant of pest damage and environmental stress.
Watering techniques also play a significant role in making the lawn less hospitable to pests. Deep and infrequent irrigation, supplying about one inch of water per week, is superior to light, daily sprinkling. Watering should be done in the early morning to allow the foliage to dry, which discourages the conditions favored by many pests and diseases.
Careful management of fertilizer application helps prevent pest outbreaks. Avoiding excessive nitrogen fertilization is important, as it promotes a flush of tender, rapid growth that is particularly attractive and vulnerable to chewing insects. A balanced fertilization program, guided by soil testing, supports the overall health and natural defenses of the turf.