Triclopyr is a common selective herbicide used widely to control broadleaf weeds and woody plants, but it is frequently applied in turf settings. While triclopyr is highly effective at eliminating tough weeds like clover, ground ivy, and brush, it is formulated to be tolerated by most established turfgrass species. The effectiveness of triclopyr in a lawn environment relies entirely on its chemical selectivity, which prevents damage to the desired grass when used correctly.
How Triclopyr Selectively Targets Weeds
The herbicide triclopyr functions as a synthetic auxin, which means it chemically mimics the plant’s natural growth hormones. This mimicry is the scientific basis for its selective action. When a susceptible plant, specifically a broadleaf plant known as a dicot, absorbs triclopyr, the chemical binds to its auxin receptors. This binding overstimulates the plant’s growth mechanisms, resulting in uncontrolled and disorganized cell division and elongation.
The fatal overgrowth manifests as symptoms like stem twisting, leaf cupping, and epinastic bending, ultimately leading to the weed’s death. Grasses, which are monocots, possess a different physiology that prevents this damage. Tolerant turfgrass species have the metabolic capacity to rapidly break down the active triclopyr compound into non-toxic conjugates. This quick detoxification prevents the herbicide from accumulating to damaging levels within the grass plant’s system.
Common Turfgrasses Tolerant to Triclopyr
Triclopyr is generally safe for application on most established cool-season turfgrasses, which are common across northern regions. These include varieties such as perennial bluegrass, perennial ryegrass, and tall fescue. These grasses possess the necessary metabolic pathways to process the herbicide without suffering significant phytotoxicity when used according to label directions.
Certain warm-season grasses show a greater sensitivity to the chemical. For example, some product labels recommend caution or avoidance when applying triclopyr to:
- Bentgrass
- Bahiagrass
- Centipedegrass
- St. Augustine grass
- Zoysiagrass
While some formulations are safe for established Bermuda grass, the product label must always be consulted because tolerance levels can vary significantly. The health of the grass at the time of application is a major factor in avoiding damage.
When Triclopyr Can Damage or Kill Grass
Damage to turfgrass typically occurs when the selective nature of the herbicide is overwhelmed by specific environmental or application factors. Using a concentration that is too high, or applying the product at a rate that exceeds the label’s specifications, can overwhelm the grass’s detoxification mechanisms. This over-application can lead to the active chemical accumulating in the grass, causing temporary discoloration or, in severe cases, death.
Extreme weather conditions, particularly high heat, significantly increase the risk of turf injury. High temperatures can cause the triclopyr, especially the ester formulation, to volatilize. This vapor can drift and cause damage to non-target plants, including sensitive turf or nearby ornamental plants.
Furthermore, grass that is already stressed by drought, disease, or dormancy is far less capable of metabolizing the herbicide, making it susceptible to damage. Newly established turf, whether from seed, sod, or plugs, is particularly vulnerable to injury. Seedlings lack the robust root systems and mature metabolic function of established turf, so they cannot efficiently detoxify the herbicide. Most product labels recommend waiting a minimum of three to four weeks after seeding before applying triclopyr to allow the grass to become well-established. Another risk is runoff or spray drift onto desirable plants outside the application area.
Safe Application Practices for Lawn Use
The first step for safe and effective use is to meticulously read and follow the product-specific instructions on the herbicide label. The label provides the precise mixing ratios and application rates, which are tailored to minimize turf injury while maximizing weed control. Using a calibrated pump or backpack sprayer is recommended over a hose-end sprayer to ensure accurate and uniform coverage of the target area.
Application timing is critical for both effectiveness and safety, with the ideal temperature range for application being between 50 and 80 degrees Fahrenheit. The herbicide should be applied to actively growing weeds during a period of calm weather to prevent spray drift. Avoid mowing the lawn for one to two days both before and after application, which allows the weed to absorb the maximum amount of product. Finally, do not apply the product if rainfall is expected within four hours, and delay any irrigation for at least 24 hours after treatment.