The frustration of finding an aggressive, persistent grassy weed spreading through a healthy lawn or garden is common for homeowners. The name “spider grass” often describes perennial grasses that spread aggressively, sending out runners that look like spider legs across the soil surface. Unlike annual weeds, these perennial invaders return year after year, establishing deep root systems or underground storage organs that make them difficult to eliminate. Regaining control requires a multi-step approach combining identification, physical removal, cultural changes, and targeted chemical treatments.
Identifying Your Specific “Spider Grass”
Eradication efforts must begin with accurately identifying the specific type of grass, as control methods vary significantly between species. The two most common perennial grassy weeds mistaken for “spider grass” are Dallisgrass and Bermudagrass.
Dallisgrass (Paspalum dilatatum) grows in distinct, tough clumps and is characterized by its coarse texture and a lighter green color compared to many turf varieties. Its most telling feature is the upright seed head, which has several short, drooping spikelets branching off the top of the stalk, often appearing from late spring through fall.
Bermudagrass (Cynodon dactylon) is aggressive, defined by its extensive network of both above-ground runners (stolons) and below-ground stems (rhizomes). These stolons rapidly creep along the soil, rooting at the nodes to form new plants, giving it a distinct spider-like spread. The leaves are typically dark green and finely textured. Correctly diagnosing the weed determines whether you focus on clump removal for Dallisgrass or the systemic control necessary for the vast underground network of Bermudagrass.
Cultural and Physical Control Techniques
Non-chemical methods are the first step against persistent perennial grassy weeds, focusing on removing existing plants and creating an environment where desirable plants can outcompete the invader. For small, isolated clumps, physical removal is the most reliable method, but it must be thorough. Use a shovel or hand trowel to dig out the entire plant, ensuring all rhizomes and stolons are extracted, which can be surprisingly deep. Any fragments of these underground stems left behind can easily sprout a new plant, requiring careful inspection of the removed soil.
Adjusting your cultural practices can also significantly suppress weed growth by favoring your lawn or garden plants. Mowing your turf at the highest recommended height, typically three to four inches, shades the soil surface. This shading prevents weed seeds from germinating and limits sunlight reaching the runners of aggressive grasses. Proper deep watering, aiming for one to one-and-a-half inches of water applied once per week, encourages deep root growth in your turf, making it far more resilient and competitive.
In garden beds or heavily infested areas, soil solarization offers an effective, chemical-free way to sterilize the top layer of soil. This process involves clearing the area, wetting the soil thoroughly, and covering the section with a clear plastic tarp, securing the edges tightly to trap heat. During the hottest part of the summer, the sun’s energy heats the soil beneath the plastic to temperatures lethal to weed seeds, seedlings, and shallow rhizomes. Leaving the plastic in place for four to six weeks during peak summer can reduce the weed seed bank before replanting.
Targeted Chemical Solutions
When dealing with widespread or deeply established perennial grassy weeds, chemical intervention is often necessary, requiring targeted post-emergent herbicides. Application must be precise because few selective herbicides kill a grassy weed without damaging the surrounding desirable grass. For warm-season turfgrasses (Bermudagrass, Zoysiagrass, St. Augustinegrass), specialized products containing active ingredients like thiencarbazone-methyl or trifloxysulfuron-sodium can control Dallisgrass. These selective herbicides inhibit specific enzymes in the weed but typically require multiple applications for complete control.
For cool-season lawns, such as Tall Fescue or Kentucky Bluegrass, selective control of invading grasses like Bermudagrass is difficult. Herbicides containing fluazifop are used to suppress or slowly eliminate aggressive warm-season grasses over several applications. Timing is important for all treatments, as applications made in late summer or early fall are often more effective. During this period, perennial weeds actively translocate nutrients down to their rhizomes and roots for winter storage, pulling the systemic herbicide deeper into the plant.
Non-selective herbicides, like those containing glyphosate, are a viable tool for spot treatment or larger area clearing. Glyphosate kills nearly all plants it contacts by inhibiting an enzyme pathway necessary for protein synthesis, so it must be applied directly to the weed foliage, avoiding overspray. An exception is applying glyphosate to Bermudagrass in the winter when the turf is completely dormant, killing green weeds like Dallisgrass without harming the sleeping Bermudagrass. Always read and follow the label instructions precisely, including wearing appropriate safety gear and adhering to reapplication schedules, which are often necessary to break the perennial weed’s cycle of regrowth.