St. Augustine grass is a favored warm-season turfgrass, appreciated for its lush appearance and adaptability. This grass variety is susceptible to various insect pests that can inflict substantial damage if unaddressed. Understanding these common pests and their impact is important for maintaining a healthy lawn.
Identifying Common St. Augustine Grass Pests
Identifying specific pests is the first step in protecting your St. Augustine lawn, as different insects cause distinct damage and require tailored approaches. Early detection helps prevent widespread issues.
Chinch Bugs
Chinch bugs are tiny insects, about 1/8 to 1/10 of an inch long, with black bodies and white wings marked with an hourglass shape. Their immature nymphs are smaller, wingless, and range from yellow to pinkish-red with a light band. These pests prefer hot, dry areas. They feed by sucking plant sap and injecting toxic saliva, disrupting the plant’s water system.
Damage appears as irregular, expanding patches of yellowing or browning grass that do not respond to watering. These patches often have a halo of yellowing or orange grass at their edges. The grass may appear stunted or dead. To confirm their presence, part the grass at the edge of damaged and healthy areas to look for the tiny, fast-moving insects. Alternatively, perform a “flotation test” by placing a metal cylinder into the soil and filling it with water, forcing the bugs to the surface.
Sod Webworms
Sod webworms are the larval stage of small, tan to white moths that fly in a zig-zag pattern, especially in the evening. The larvae, which cause damage, are light green to gray-green with dark spots, growing up to one inch long. They are most active at night, chewing off grass blades and stems just above the crown.
Evidence includes ragged chewing damage on grass blades and small brown patches of closely clipped grass, resembling drought stress. Injured areas enlarge and merge into bigger patches. You might also find silken tunnels or small, bright green fecal pellets (frass) within the thatch layer, where larvae hide during the day.
Armyworms
Armyworms are caterpillars, the larval stage of moths. The larvae vary in color from light green to olive green or nearly black, often displaying distinct white or yellow stripes along their sides. Mature larvae can reach up to 1.5 inches in length and may have an inverted Y-shaped marking on their heads.
These pests cause rapid defoliation, often eating grass blades down to the crown. Damage appears as irregular brown patches that can spread quickly. Armyworms are most active during late evening and early morning. Increased bird activity on your lawn can also indicate an armyworm presence, as birds feed on the caterpillars.
Grub Worms (White Grubs)
Grub worms are C-shaped larvae of various scarab beetles, typically white or off-white with a brown head and three pairs of legs. They feed on grass roots, compromising the plant’s ability to absorb water and nutrients.
Signs of grub damage include patches of wilting, discolored grass that turns yellow and then brown, even with adequate watering. The turf in affected areas often feels spongy underfoot. The grass can be easily lifted or rolled back like a carpet due to the severed root system. Finding five or more grubs per square foot when digging into the soil a few inches deep confirms an infestation.
Mole Crickets
Mole crickets are distinctive burrowing insects, about 1 to 2 inches long, with a gray-brown, velvety body and large, shovel-like forelegs adapted for digging. They tunnel through the soil just beneath the surface, disrupting grass roots. While they feed on roots, their primary damage comes from tunneling.
Evidence includes raised burrows or tunnels, small mounds of displaced soil, and brown, dry, or dead patches of grass. The affected turf may feel spongy due to loosened topsoil. This tunneling can uproot plants, causing the grass to dry out and die.
Preventing and Managing St. Augustine Grass Pests Without Chemicals
Cultural practices deter pests and foster a resilient St. Augustine lawn. A healthy lawn better withstands pest pressure, reducing the need for chemical interventions.
Proper Mowing
Maintaining the correct mowing height for St. Augustine grass is important. A height of 2.5 to 4 inches is generally recommended. Taller grass shades the soil, conserving moisture, suppressing weeds, and encouraging deeper root growth. Regularly sharpening mower blades ensures a clean cut, minimizing stress on the grass.
Appropriate Watering
Deep and infrequent watering encourages St. Augustine grass to develop strong, deep root systems. The lawn typically needs about 1 to 1.5 inches of water per week, applied in two or three sessions, rather than frequent, shallow watering. Watering early in the morning is ideal as it minimizes water loss to evaporation and allows grass blades to dry before evening, reducing fungal disease risk. Overwatering can lead to shallow root growth and create moist conditions some pests and diseases prefer.
Balanced Fertilization
Proper nutrient levels maintain plant vigor and resistance to pest damage. St. Augustine grass typically requires 2 to 4 pounds of nitrogen per 1,000 square feet annually, with applications spread throughout the growing season. Balanced fertilization promotes robust growth without encouraging tender foliage that can attract certain insects. Excessive nitrogen can make the grass more susceptible to some pests. Regular soil tests help determine precise nutrient needs and pH levels, optimizing nutrient uptake and overall lawn health.
Dethatching and Aeration
Dethatching involves removing the layer of dead and living organic matter (thatch) that accumulates between the soil surface and the green grass blades. A thick thatch layer can harbor pests and prevent water, air, and nutrients from reaching the soil and roots. Aeration creates small holes in the soil, improving air circulation, water penetration, and nutrient absorption. These practices reduce hiding spots for pests and promote a healthier environment for beneficial soil organisms.
Beneficial Insects
Encouraging natural predators is a non-chemical control method. Many beneficial insects, such as ladybugs and parasitic wasps, prey on common St. Augustine grass pests. Creating a diverse landscape with flowering plants can attract these helpful insects, supporting a natural balance. Identifying beneficial insects from harmful ones is important to avoid inadvertently harming them.
Chemical Control for St. Augustine Grass Pests
When cultural practices are insufficient, chemical controls can be used as a targeted solution for St. Augustine grass pests. These products manage infestations too severe for non-chemical methods alone.
Types of Pesticides
Various types of pesticides are available, including granular, liquid, systemic, and contact formulations. Granular products are spread and often require watering to activate. Liquid concentrates are mixed with water and sprayed. Systemic insecticides are absorbed by the grass, killing pests that feed on it. Contact insecticides work by direct application to the pest or treated surface. Common active ingredients include bifenthrin, carbaryl, cyfluthrin, lambda-cyhalothrin, and permethrin.
Application Guidelines
Careful adherence to product labels is important when applying pesticides. The label provides instructions on proper timing and correct dosage rates for effective control. For liquid sprays, ensuring even coverage is important. Watering the lawn before a liquid application can help the pesticide penetrate the turf, but irrigation immediately after is generally not recommended. Spot treatments are effective for localized infestations, targeting affected areas and a buffer zone.
Safety Precautions
Wearing appropriate protective gear, such as unlined, chemical-resistant gloves, long pants, shirts, shoes, and socks, is important when mixing and applying pesticides. Keep children and pets off treated areas until the product has dried or for the re-entry time specified on the label. Avoiding application on windy days helps prevent drift. Proper disposal of empty containers and unused chemicals according to label directions is necessary to protect the environment.
Professional Help
Consulting a lawn care professional or local extension office can be beneficial for severe or persistent infestations. Professionals can accurately identify the specific pest and recommend the most effective chemical treatment. They have access to a wider range of products and specialized equipment for challenging situations.
Adopting Integrated Pest Management for Your Lawn
Integrated Pest Management (IPM) offers a framework for managing St. Augustine grass pests. This approach combines various strategies to maintain a healthy lawn while minimizing environmental impact. IPM emphasizes pest identification, cultural practices, and biological controls as primary defenses. Chemical treatments are considered when necessary, serving as a last resort. The goal of IPM is to control pest populations effectively, reducing risks to the environment and promoting the long-term health of your lawn.