Tenacity is a selective herbicide containing the active ingredient mesotrione. It functions as both a pre-emergent and post-emergent weed control product, targeting specific weeds while leaving certain turfgrasses unharmed. Homeowners frequently ask whether this chemical can be safely applied to Bermuda grass without causing permanent damage.
The Safety Verdict on Bermuda Grass
Tenacity can be used on Bermuda grass, but application requires careful adherence to specific guidelines to prevent injury. The herbicide works by inhibiting the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD) in susceptible plants.
This enzyme is necessary for the production of carotenoids, which are protective pigments in the plant’s chloroplasts. When the HPPD enzyme is blocked, the plant cannot produce these pigments, leading to the destruction of chlorophyll by sunlight.
Bermuda grass, while tolerant of mesotrione, will often exhibit this bleaching effect after treatment. The grass blades will turn a noticeable white or light yellow color, typically starting a few days after application.
This discoloration is a cosmetic, temporary reaction, not an indication of permanent damage to the turf. Homeowners should expect the Bermuda grass to maintain this bleached appearance for approximately two to three weeks before new, green growth emerges and the lawn recovers its uniform color.
Critical Application Factors for Safety
Ensuring the safety of Bermuda grass depends entirely on precise application, starting with the dosage. It is imperative to use the lowest recommended rate specified on the product label for warm-season grasses like Bermuda. Over-application is the primary cause of severe or permanent turf injury, as it overwhelms the grass’s ability to metabolize the chemical.
Temperature is another factor that dictates safe use. Applying Tenacity when air temperatures consistently exceed 85°F to 90°F significantly increases the risk of permanent damage. High heat stresses the Bermuda grass, making it less capable of recovering from the chemical stress. Applications should be scheduled during cooler periods of the year or day to minimize this risk.
The maturity of the turf also plays a role in its tolerance to mesotrione. Tenacity should only be applied to Bermuda grass that is fully established and actively growing. It must never be used on newly seeded, sodded, or sprigged Bermuda grass, as young plants lack the resilience to withstand the chemical’s effects. Applying to immature turf will likely result in plant death rather than temporary bleaching.
For post-emergent weed control, a non-ionic surfactant (NIS) is necessary to help the herbicide stick to the weed foliage. While the NIS improves efficacy, it also increases the chemical’s uptake by the Bermuda grass. This increased absorption heightens the likelihood and severity of the temporary bleaching effect, reinforcing the need to maintain the lowest effective dosage.
Weeds Controlled and Expected Discoloration
Tenacity provides excellent control of grassy weeds such as crabgrass and goosegrass, especially when applied as a pre-emergent barrier. It is also effective against broadleaf weeds, including clover, chickweed, and nimblewill, when used as a post-emergent treatment.
For pre-emergent control, the chemical is applied before weed seeds germinate, preventing emergence. For post-emergent control, the herbicide is absorbed by existing weed foliage, initiating the bleaching process. The weeds themselves will turn white or clear before they die off completely, which can take up to three weeks.
The bleaching of the Bermuda grass typically peaks around seven to ten days after application. This temporary discoloration is a sign that the chemical is active in the plant tissue and confirms the grass is metabolizing the mesotrione.
Following application, proper cultural practices help ensure the Bermuda grass recovers quickly. Avoid mowing the lawn for a few days after treatment to allow maximum herbicide absorption. The lawn should not be under drought stress, as adequate moisture supports the metabolic processes necessary for recovery and the growth of new, green tissue.