Pesticide Classification
_X Herbicide __ Fungicide
__ Bactericide
__ Insecticide/Miticide
__ Molluscicide __ Repellent
Properties Properties Properties
_X Selective
__ Non-selective

_X Pre-emergent
_X Post-emergent

_X Systemic
_X Contact
__ Broad Spectrum
__ Specific

__ Systemic
__ Non-systemic

__ Protectant
__ Eradicant
__ Synthetic
__ Biological
__ Oil
__ Soap
__ Botanical
__ Other
__ Broad-spectrum
__ Specific

__ Systemic
__ Non-systemic

__ Contact poison
__ Stomach poison
__ Other

Common Brand Names:


 Chemical Action and Usages: Tenacity (active ingredient mesotrione) is a systemic pre-emergence and post-emergence herbicide for the selective contact and residual control of weeds in turfgrasses. It has pre- and post-emergence activity on 46 monocot (grassy type) and dicot (broadleaf) weed species. It can selectively control perennial monocots (nimblewill, annuals such as crabgrass and goosegrass, and yellow nutsedge) in many turf species. Tenacity is only labeled for use on the following cool-season grasses grown in the St. Louis area: Kentucky bluegrass, perennial ryegrass, turf type tall fescues and fine leaf fescues. It is not labeled for use on the warm-season grasses of Bermuda and Zoysia.

When used as a post-emergence, susceptible weeds absorb Tenacity through foliar contact and root uptake. Tenacity quickly translocates throughout the plant after application. Weed growth is quickly suppressed after application, as photosynthesis is disrupted. Foliage of treated weeds turn white from lack of chlorophyll (bleached appearance) and the weeds die within two to three weeks. Tenacity may also cause temporary slight whitening of the foliage of the desired turfgrass. These symptoms usually appear 5-7 days after application and may last for several weeks.

To effectively control nimblewill, repeat applications at two- to three-week intervals may be needed. Best control is obtained when applying to actively growing weeds. A non-ionic surfactant should be added to the spray mix being applied to the targeted weed.

Cautions/Instructions: Read the label carefully and apply the product according to the directions on the label. Tenacity is a very concentrated chemical so extremely accurate measurements of both the herbicide and surfactant are needed to avoid significant desirable turf damage. Do not apply directly to water or to areas where surface water is present. This product has a high potential for runoff. Runoff will be reduced by avoiding applications when rainfall or irrigation is expected to occur within 48 hours of applications. When using this product as a post-emergence, applications should be made to the targeted weed rather than as a broadcast application. Do not use grass clippings from treated turf as mulch around trees or in vegetable gardens.

Toxicity: Can cause mild eye and skin irritation. Prolonged and/or repeated skin contact may cause allergic reaction in some individuals.  Applicators should wear long pants, a long-sleeved shirt, chemical resistant gloves and eye protection when applying this product.