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Syngenta Tenacity® Herbicide Q&A

Syngenta Tenacity® Herbicide
Q         What is Tenacity?

Tenacity® herbicide is a new tool for lawn care operators for pre- and post-emergence weed control on cool-season turfgrasses such as tall fescue perennial ryegrass and Kentucky bluegrass.
Granted reduced-risk status by the U.S. Environmental Protection Agency (EPA), Tenacity (mesotrione on turf) can be used at seeding, including bare-ground seeding, or selective renovations and overseeding. It keeps weeds from germinating and allows new grass to flourish.
Q         What does it mean when the EPA says that Tenacity was granted Reduced Risk status? How did Tenacity earn this status?
A         The active ingredient in Tenacity, mesotrione, has been granted Reduced Risk status by the EPA for turf use. It has favorable ecotoxicity and human health profiles, compared to many registered herbicides, which result in a reduction in the herbicide load on the environment. Its mode of action is novel among turf herbicides, and it fits well into IPM and resistance management strategies.*
*A Reduced Risk pesticide use is defined as one which may reasonably be expected to accomplish one or more of the following: (1) reduces pesticide risks to human health; (2) reduces pesticide risks to non-target organisms; (3) reduces the potential for contamination of valued, environmental resources, or (4) broadens adoption of IPM or makes it more effective. Mesotrione qualifies under one or more of the above criteria.
Q         How does Tenacity work? What is the mode of action?
A         Tenacity with a group 27 mode of action inhibits a plant enzyme called HPPD that is essential to photosynthesis and prevents formation of carotenoids in susceptible plant species. Without carotenoids, light energy and by-products of photosynthesis will destroy chlorophyll and cell membranes. This results in bleaching of leaves, followed by necrosis and death of the plant.

Q         How was Tenacity herbicide discovered?
A          A Syngenta scientist in California observed that there were fewer weeds growing under his bottlebrush (Callistemon citrinus) plant, far fewer than can be explained by shading alone. He concluded that the plant must be producing allelochemicals to suppress weed competition. Syngenta synthesized mesotrione, based on the allelochemicals produced by the bottlebrush plant.
Q         How quickly does Tenacity work?
A         Once absorbed, Tenacity quickly translocates throughout the plant. Weeds stop competing with the desirable turf soon after application, as photosynthesis is disrupted. Death of the unwanted plant usually occurs within two or three weeks.
Q         What weeds does Tenacity control?
A         Mesotrione, the active ingredient in Tenacity, controls 46 dicot and monocot broadleaf, sedge weeds and grasses, including nimblewill, crabgrass, bentgrass, ground ivy, yellow foxtail and yellow nutsedge.
Q         Lawn care operators and their customers may see some bleaching or “whitening” of weeds after an application of Tenacity. Is that normal?
A         Yes — it means that Tenacity is working. Some degree of turf bleaching is to be expected when using the product, since its mode of action