1. Field of the Invention
The present invention relates generally to granular compositions containing mesotrione herbicides and to methods for the use thereof. More particularly, the compositions of this invention comprise herbicidal mixtures of mesotrione impregnated into or coated on the surface of a granular substrate material such as a fertilizer granule for use to control weeds in turfgrasses without causing damage to the grass.
2. Description of Related Art
Mesotrione is a triketone compound having the chemical structure of (2-[4-methylsulfonyl-2-nitrobenzoyl]-1,3-cyclohexane dione) employing CAS nomenclature. A liquid product containing 40 weight percent mesotrione is being sold under the trademark Callisto® by Syngenta Crop Protection, Inc. as a systemic pre-emergence and post-emergence herbicide for the selective contact and residual control of broadleaf and grassy weeds in field corn, production seed field corn, field corn grown for silage, yellow popcorn and sweet corn. In the context of the present invention, the term “mesotrione” is intended to refer to the triketone compound itself as well as to all formulations containing such compound.
U.S. Pat. No. 5,006,158 describes a wide variety of compounds including mesotrione which are useful as herbicides and can be applied in a variety of ways at various concentrations. The compounds or salts thereof described in U.S. Pat. No. 5,006,158 are described as being formulated into herbicidal compositions, by admixture, in herbicidally effective amounts, with adjuvants and carriers normally employed for facilitating the dispersion of active ingredients for agricultural applications and acknowledges the fact that the formulation and mode of application of such active ingredients may affect the activity of the materials in a given application.
U.S. Pat. No. 5,006,158 further discloses that the diverse active herbicidal compounds or salts disclosed therein can be formulated as granules of relatively large particle size, as wettable powders, as emulsifiable concentrates, as powdery dusts, as flowables, as solutions or as any of several other known types of formulations, depending upon the desired mode of application. The formulations containing the actives are disclosed to contain as little as about 0.5% to as much as about 95% or more by weight of active ingredient. A herbicidally effective amount of the actives is disclosed as depending upon the nature of the seeds or plants to be controlled and the rate of application varies from about 0.01 to approximately 10 pounds per acre, preferably from about 0.02 to about 4 pounds per acre.
Granular formulations wherein the actives are carried on relatively coarse particles as disclosed in U.S. Pat. No. 5,006,158 are usually applied without dilution to the area in which suppression of vegetation is desired. Typical carriers for such granular formulations as described in U.S. Pat. No. 5,006,158 include sand, fuller's earth, attapulgite clay, bentonite clays, montmorillonite clay, vermiculite, perlite and other organic or inorganic materials which absorb or which may be coated with the toxicant. These granular formulations are normally prepared to contain about 0.1% to about 25% of active ingredients which may include surface-active agents such as heavy aromatic naphthas, kerosene or other petroleum fractions, or vegetable oils; and/or stickers such as dextrins, glue or synthetic resins.
In U.S. Pat. No. 6,890,889, herbicidal formulations comprising mesotrione in combination with an adjuvant system were disclosed to optimize post emergent activity on broadleaved weeds in corn. The preferred adjuvant system to optimize weed control and minimize crop response was disclosed to be a crop oil concentrate (COC). Other adjuvant systems for use in the formulation may comprise liquid compositions such as methylated seed oil (MSO), urea ammonium nitrate (UAN) and ammonium sulfate (AMS). No granular formulations are disclosed.
In Published U.S. Patent Application US 2005/0096226, herbicidal compositions useful for controlling weeds in growing crops such as maize (corn) comprising triketone products including mesotrione in combination with an organic phosphate, phosphonate or phosphinate adjuvant were disclosed which can be prepared as a pre-mix concentrate for formulation in various forms including granular formulations with typical carriers such as sand, fuller's earth, attapulgite clay, bentonite clays, montmorrilonite clay, vermiculite, perlite and other organic or inorganic materials which absorb or which can be coated with the active compound.
However, it appears that mesotrione applied as a liquid in spray form as described in U.S. Pat. Nos. 5,006,158, 6,890,889 and in Published U.S. Patent Application US 2005/0096226 is not effective for use in controlling weeds in turfgrasses without causing unacceptable injury to the grasses. Specifically, previously known mesotrione containing formulations in spray form have demonstrated unacceptable levels of damage/phytotoxicity to a range of turfgrass varieties. Turfgrass varieties as referred to herein include perennial ryegrass (Lolium perenne), fine fescue (Festuca spp.), Kentucky bluegrass (Poa pratensis), tall fescue (Festuca arundinacea), zoysiagrass (Zoysia spp.), St. Augustinegrass (Stenotaphrum secundatum), centipedegrass (Eremochloa ophiuroides), and the like and mixtures thereof. In view of this perceived shortcoming of prior liquid mesotrione containing formulations, mesotrione sprays have not been considered to be capable of being employed broadly for effective herbicidal treatment in turfgrass varieties.
Thus, it would be advantageous to provide granular compositions containing mesotrione as an active herbicidal ingredient which can be used to control weeds in turfgrasses such as perennial ryegrass, fine fescue, Kentucky bluegrass, tall fescue, zoysiagrass, St. Augustinegrass, centipedegrass and the like and mixtures thereof without causing unacceptable phytotoxic levels of damage to these grasses.