Dicamba is a widely used herbicide designed to manage broadleaf weeds in turf and agricultural settings. This chemical is often included in selective weed control products for lawns, leading many homeowners to wonder whether it poses a risk to their desired grass. Understanding how Dicamba interacts with different plant types is key to determining if your lawn is safe from potential harm. The answer depends entirely on the application method, the concentration used, and the maturity of the grass itself.
Understanding How Dicamba Works
Dicamba is classified as a synthetic auxin, a type of herbicide that mimics natural plant hormones regulating cell division, growth, and differentiation. The herbicide is designed to mimic these regulators, but it does so in excessive and uncontrolled amounts.
When a sensitive plant absorbs Dicamba through its leaves or roots, the chemical is rapidly translocated throughout the plant’s vascular system to areas of new growth. This systemic movement causes a massive hormonal overload, forcing the plant’s cells to grow abnormally and uncontrollably. This destructive growth quickly exhausts the plant’s resources, leading to the collapse of its internal structures and death.
This mechanism explains why Dicamba is considered a selective herbicide, primarily targeting broadleaf plants (dicots). Monocots, which include all turfgrass species, possess a different physiological structure and the ability to metabolize the chemical more rapidly, making them tolerant to the herbicide when applied correctly.
Dicamba’s Effect on Established Grasses
When applied at the recommended label rates, Dicamba is safe for most established turfgrass varieties. Common lawn grasses, including fescue, Kentucky bluegrass, Bermuda, and ryegrass, exhibit natural tolerance to the herbicide. This tolerance results from distinct metabolic pathways, which allow the grass plant to quickly process and chemically deactivate the Dicamba molecule.
The speed at which the grass metabolizes the herbicide prevents the chemical from accumulating to levels that would cause lethal hormonal disruption. The environment created by the dense turfgrass stand also contributes to safety, as Dicamba’s biodegradation rate is significantly faster in the organic thatch layer of turfgrass compared to deeper soil.
This safety does not apply to all grass types. Certain warm-season grasses, notably St. Augustinegrass and Bentgrass, are highly sensitive to Dicamba and should not be treated with products containing the herbicide. Product labels specify these exceptions, and ignoring them can result in severe damage or complete dieback of the lawn.
Scenarios That Cause Grass Injury
While established grasses are tolerant, several specific scenarios can lead to injury or death of the turf.
Over-Application
The most common cause of damage is the over-application of the product, which overwhelms the grass’s detoxification capacity. Applying a concentration higher than the rate listed on the product label introduces a dose of the synthetic auxin that the grass cannot metabolize quickly enough, causing disruptive growth.
Young Grass
Newly seeded or young grass is also highly vulnerable to Dicamba exposure. Seedlings lack the mature metabolic machinery and root systems necessary to rapidly process the chemical, making them susceptible to damage. Product labels strictly advise against applying Dicamba until the turf is well-established, usually after several mowings.
Drift and Volatilization
Another frequent cause of widespread injury is the movement of the chemical off the target area, known as drift or volatilization. Dicamba is a volatile compound, meaning it can turn from a liquid spray into a gas, particularly when temperatures are high. This vapor can be carried by the wind for significant distances, causing damage to non-target plants, including neighboring lawns and sensitive ornamentals.
When a turfgrass lawn is injured by Dicamba, the symptoms relate to hormonal disruption. Affected grass often displays twisted, curled, or stunted growth tips, sometimes with the leaves cupping upward. The roots may also be stunted or display abnormal development, which impairs the plant’s ability to absorb water and nutrients.
Post-Application Grass Care
If a lawn has been injured by accidental over-application or exposure to Dicamba drift, immediate steps can mitigate the damage and promote recovery. The first step involves removing the chemical from the grass and soil before it can be fully absorbed. This is accomplished by heavy watering, which helps to flush the Dicamba deeper into the soil profile where it is rapidly degraded by soil microbes.
Following the flushing, promoting the grass’s recovery is the focus. Apply a light application of nitrogen fertilizer, typically one or two weeks after the exposure. This nutrient boost provides the necessary energy for the turf to produce new, healthy leaves and shoots to replace the damaged tissue.
Further stress on the recovering turf should be avoided by raising the mowing height and reducing mowing frequency for up to three weeks. If the damage is severe enough to require re-seeding, a waiting period is necessary. A standard recommendation is to wait at least three weeks after the Dicamba application before planting new grass seed to ensure residual herbicide does not inhibit germination.