No. 1 Article 9/March 23, 2007

Herbicide Changes for the 2007 Illinois Agricultural Pest Management Handbook

We begin the new season of weed-related articles for the Bulletin with an overview of changes in herbicide options available to Illinois weed control practitioners. The number of new herbicide active ingredients is limited, and some of these products were actually commercially available in 2006 but not included in the Illinois Agricultural Pest Management Handbook until this year. This article is not intended to provide a complete summary of all label changes that have occurred, and we encourage all who use herbicides to consult respective product labels for full information.

Impact 2.8SC (topramezone) became commercially available in 2006. Impact provides postemergence control of certain annual grass and broadleaf weed species in corn. Topramezone controls susceptible weeds by inhibiting the formation of specific plant pigments, similar to the mode of action of mesotrione. Impact will often be used in tank mixes with other herbicides (especially atrazine) to broaden the weed control spectrum. It has shown good efficacy on such broadleaf species as velvetleaf, smartweed, pigweed, common ragweed, lambsquarters, and cocklebur as well as on certain annual grasses, such as giant foxtail. Applications can be made to corn up to 45 days before harvest, but they are limited to corn up to 12 inches high if tank-mixed with atrazine. Application rates range from 0.5 (north of Interstate 80) to 0.75 fluid ounce per acre, and spray additives (such as COC or MSO in combination with an ammonium nitrogen fertilizer) are required. This active ingredient demonstrates soil persistence, which may be prolonged under dry soil conditions.

Canopy 75DG (chlorimuron + metribuzin) was "reintroduced" into the soybean herbicide market during 2006 by DuPont. Product formulation, rate structure, and label are very similar to when the product was removed from the market a few years ago.

Canopy EX (chlorimuron + tribenuron) has been positioned primarily as a fall-applied herbicide option. Since its introduction into the Illinois market, the product label has carried a 45-day interval that must elapse between application and soybean planting. Recently the interval has been reduced to 7 days. Table 1 details a comparison of Canopy and Canopy EX active ingredients, based on application rate.

Authority First and Sonic 70DF (sulfentrazone + cloransulam) are premix products marketed by FMC and Dow AgroSciences, respectively. These products are labeled for soil applications (PPI or PRE) prior to soybean emergence. Application rates are determined by soil organic matter, up to a maximum of 8 ounces per acre. As an example, 6.45 ounces of either of these products will provide 0.25 lb ai sulfentrazone and 0.032 lb ai cloransulam, equivalent to 5.33 ounces of Authority 75DF and 0.6 ounce of FirstRate 84WDG, respectively. The product will likely be positioned as a "set-up" treatment at a reduced application rate (around 3 ounces) for early-season control of waterhemp prior to the initial postemergence glyphosate application, or at higher application rates when used in conventional soybean production systems. See Table 2 for specifics on active ingredients of Authority First and Sonic 70DF by application rate.

Status (dicamba + diflufenzopyr + safener) contains the same active ingredients as Distinct and is formulated with a safener to reduce the potential for corn injury. Applications can be made to corn between 4 and 36 inches high (V2 to V10) at rates from 5 to 10 ounces per acre. Include a spray additive (such as NIS, COC, or MSO) and an ammonium nitrogen source with all applications. A 5-ounce rate of Status provides the same amount of dicamba and diflufenzopyr as a 4-ounce rate of Distinct. Table 3 compares Distinct and Status active ingredients based on application rate.

Prefix CP (fomesafen and S-metolachlor) is a co-pack product for preemergence applications in soybean. The product contains the active ingredients of Reflex/Flexstar and Dual Magnum and is designed to provide residual control of certain annual grass and broadleaf weed species. A typical application rate of Prefix would provide the equivalent of 1 pint of Dual Magnum and 1 pint of Reflex. Sale of a formulated product containing these active ingredients is anticipated in 2008.

Valor XLT (flumioxazin + chlorimuron) is a new premix product from Valent that contains the active ingredients of Valor and Classic. Valor XLT application rates range from 3 to 5 ounces of product per acre and can be applied for burndown of existing vegetation prior to soybean planting or up to 3 days after soybean planting. Applications made after soybeans begin to emerge will result in severe crop injury. Do not apply more than 5 ounces of Valor per acre per season, or more than 2.5 ounces per acre on soils with a composite pH of greater than 6.8.

Autumn 10WDG (iodosulfuron) contains one of the active ingredients found in Equip (foramsulfuron + iodosulfuron), but not the safener formulated with Option and Equip. Autumn is positioned as a fall-applied herbicide for control of certain winter annual weed species. Currently the label allows planting only corn the spring following a fall application. The application rate of Autumn is 0.3 ounce per acre, and the product will be positioned primarily in the southern half of Illinois.

Stout mp (nicosulfuron and thifensulfuron) contains the active ingredients of Accent and Harmony GT XP. The product is labeled for postemergence applications in field corn up to 5 collars or 16 inches, at 1/2 to 3/4 ounce per acre. Applications must include either COC or NIS and an ammonium nitrogen fertilizer. The active ingredients will provide control of grass weeds and certain broadleaf species (velvetleaf, common lambsquarters, pigweed, smartweed).

SureStart is a new soil-applied corn herbicide from Dow AgroSciences that contains the active ingredients acetochlor, clopyralid, and flumetsulam. The formulation will contain 4.25 lb active ingredient per gallon and be used at rates ranging from 1.5 to 2 pints per acre. --Aaron Hager

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