Brush killers are specialized herbicides designed to eliminate woody plants, vines, and tough broadleaf weeds. Whether they will also kill grass depends heavily on the specific chemicals used in the product. Many formulations are selective, targeting broadleaf plants while leaving turfgrass unharmed. However, brush killers often contain high concentrations or non-selective components that can easily damage or kill grass, especially if not applied precisely. Careful consideration of the product’s composition and application method is required to prevent grass damage.
How Brush Killers Target Plants
Brush killers generally operate as systemic, selective herbicides, exploiting fundamental biological differences between plant types. Selective herbicides target dicots (plants with two seed leaves, like woody brush and broadleaf weeds) while sparing monocots (which include all turfgrasses). This selectivity is possible because monocots and dicots possess different metabolic pathways and structures.
The active ingredients are absorbed through the leaves, stems, or cut surfaces, then translocated throughout the plant’s vascular system. This systemic action distinguishes them from contact killers, which only destroy the tissue they touch. By moving deep into the roots and growing points, these chemicals disrupt fundamental growth processes. They often mimic natural plant hormones called auxins, causing abnormal and uncontrolled growth that leads to the death of the entire target plant.
Specific Active Ingredients and Grass Vulnerability
The risk to your lawn is directly tied to the specific active ingredients in the brush killer formulation.
Triclopyr
Many products rely on the synthetic auxin herbicide Triclopyr, which is generally safe for established cool-season grasses like Kentucky bluegrass and tall fescue. However, Triclopyr can cause significant injury to certain warm-season turf varieties, including St. Augustinegrass and centipedegrass, even at labeled concentrations. Bermudagrass can also show signs of injury, characterized by a reduction in quality and green coverage.
Dicamba and 2,4-D
Other brush killer formulations often include combinations of synthetic auxins like Dicamba and 2,4-D. When used at the low rates intended for general lawn weed control, these combinations typically spare turfgrass. However, the higher concentrations found in brush killer products can overwhelm the grass, causing temporary distortion or significant damage. This damage sometimes appears as twisted or flattened growth known as epinasty.
Glyphosate (Non-Selective)
A major risk comes from brush killers containing Glyphosate, which is a non-selective herbicide. Glyphosate works by inhibiting an enzyme pathway common to almost all plants, meaning it will kill virtually any green plant tissue it contacts, including all turfgrass types. Products labeled as “weed and grass killer” or “total vegetation killer” often contain high concentrations of Glyphosate. Any overspray or drift will result in dead patches of lawn, so it is crucial to check the ingredient list for non-selective agents.
Safe Application Strategies to Protect Turf
Protecting your lawn while using a brush killer requires careful attention to application technique and environmental conditions. Controlling spray drift is a primary precaution, as fine spray particles can be carried by wind onto desirable turf or plants. To minimize drift, use a coarse spray nozzle, maintain low spray pressure, and only apply the product on calm days with minimal wind.
Spot treatment, rather than broadcast spraying, is a safer method when working near turf. For brush and vines, consider painting the herbicide directly onto the foliage or a freshly cut stump. This direct application ensures the systemic chemical is absorbed by the target plant while avoiding contact with the grass blades.
Timing the application is equally important, as stressed grass is more susceptible to damage from selective herbicides. Avoid spraying during periods of extreme heat or drought, as the turf will lack the resilience to recover from chemical stress. Always verify the product label for warnings about specific grass types and follow directions concerning application rates and post-application watering restrictions.