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Issue No. 2, Article 5/April 4, 2008

Herbicide Updates for 2008

With the dawning of a new season of newsletter articles, we provide an overview of some changes in herbicide options available to Illinois weed control practitioners. The number of new herbicide active ingredients is limited again this year. Some of these products were actually commercially available in 2007 but were not included in the Illinois Agricultural Pest Management Handbook until the 2008 edition. 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 additional information.

Authority Assist 4SC (sulfentrazone + imazethapyr) contains the active ingredients of Authority and Pursuit. Authority Assist may be applied from 45 days before soybean planting up to 3 days after planting. For preplant incorporation applications, incorporate no deeper than 2 inches. Application rates are based on soil texture and organic matter content and range from 6 to 12 fluid ounces per acre. The addition of imazethapyr will improve control of certain large-seeded species (such as common cocklebur) over that of sulfentrazone alone.

Authority MTZ 45DF (sulfentrazone + metribuzin) contains the active ingredients of Authority and Sencor. It can be applied from up to 45 days preplant until 3 days after soybean planting. Application rates range from 8 to 20 ounces per acre and are determined by soil texture and organic matter content. Authority MTZ will suppress or control several broadleaf species, particularly small-seeded species such as common lambsquarters, pigweeds, and waterhemp. Control of large-seeded broadleaf species, such as cocklebur and giant ragweed, will probably not be adequate with this product alone. Duration of weed control will generally be directly related to product application rate and timing.

Autumn 10WDG (iodosulfuron) is now labeled for applications at least 30 days before planting field corn. Do not apply Autumn prior to planting sweet corn, popcorn, or corn grown for seed.

Breakfree 6.4EC (acetochlor), Breakfree ATZ 5.25L, and Breakfree ATZ Lite 5.5L (acetochlor + atrazine) contain the same active ingredients as Surpass, Keystone, and Keystone LA, respectively.

Distinct 70WDG (dicamba + diflufenzopyr) can be applied at 2 to 4 ounces per acre prior to soybean planting for control of existing vegetation. Following this type of application, a minimum of one inch precipitation (rainfall or overhead irrigation) and a 30-day waiting interval are required before planting soybean. These requirements must be satisfied to reduce the potential for soybean injury.

Enlite and Envive (chlorimuron + flumioxazin + thifensulfuron) are new soybean herbicide premixes from DuPont. Both products contain the same active ingredients, but the ratios are such that Enlite is better suited to northern areas and higher pH soils (i.e., less chlorimuron), while Envive will be positioned across a broader geography of Illinois. Each product can provide burndown and soil-residual control of many annual broadleaf weed species. Envive 41.3DG can be applied from prior to planting until 3 days after planting but before soybeans emerge. Application rates range from 2.5 to 5.3 ounces per acre but should not exceed 2.5 ounces for soils with a composite pH of greater than 7.0.

Halex GT 4.38CS (S-metolachlor + glyphosate + mesotrione) is a postemergence premix for control of a broad spectrum of grass and broadleaf weed species in glyphosate-resistant corn hybrids. Halex GT can be applied at 3.6 to 4.0 pints per acre to corn from emergence up to 30 inches in height or the 8-leaf stage. Best results will often be achieved when Halex GT is applied before weeds exceed 4 inches in height. Applications must include a nonionic surfactant and ammonium sulfate. An application rate of 3.6 pints per acre provides the equivalent of 1 pint of Dual II Magnum + 3 fluid ounces of Callisto + 0.95 lb ae glyphosate. The S-metolachlor and mesotrione components may provide some level of residual weed control following application.

Laudis 3.5SC (tembotrione) is a new postemergence herbicide registered for use in field and silage corn, seed corn, sweet corn, and popcorn for control of certain annual broadleaf and grass weed species. Laudis causes whitening or bleaching in susceptible species by inhibiting 4-HPPD (the same target site as Callisto and Impact). The commercial formulation contains a safener that reduces the potential for corn injury. The application rate is 3 fluid ounces per acre when applied alone or 2 fluid ounces when tankmixed with Liberty and applied to Liberty Link corn hybrids. Atrazine (0.5 lb ai/acre) is often a preferred tankmix partner and can enhance the control of several weed species. All applications should include the appropriate spray additive(s), which is determined by choice of tankmix partner. Applications of Laudis alone or tankmixed with atrazine should include a crop oil or methylated seed oil concentrate and an ammonium nitrogen fertilizer. Broadcast applications of Laudis can be made to field corn or popcorn from emergence up to the V8 growth stage and to sweet corn from emergence up to the V7 growth stage. Do not make more than two applications of Laudis to field corn or popcorn or one application to sweet corn per growing season. University of Illinois research has shown Laudis to have activity on broadleaf species similar to Callisto and Impact and grass control better than Callisto. Fall panicum is one particular annual grass species that is very tolerant to Laudis.

SureStart 4.16SE (acetochlor + clopyralid + flumetsulam) is a premix product for use only in herbicide-tolerant field corn and silage corn. SureStart can be applied preplant (up to 30 days prior to planting) or postemergence (to corn up to 11 inches tall) at 1.5 to 2 pints per acre. The 1.5 pints per acre rate of SureStart provides the equivalent of 0.88 pint Surpass + 0.45 ounce Python + 2.32 ounces Stinger. These rates will generally provide early-season control or suppression of weeds, but plan to follow up with a timely postemergence herbicide application. SureStart was labeled in 2007, but the current growing season marks its first full season of commercialization.

Prefix 5.3EC (S-metolachlor + fomesafen) contains the active ingredients found in Dual Magnum and Reflex. This premix can be applied preplant or preplant incorporated for control of annual grass and broadleaf weed species in soybean. Application rates will vary in Illinois, ranging from a maximum of 3 pints per acre south of Interstate 70 to a maximum of 2.5 pints per acre north of I-70. This formulation of Prefix replaces the co-pack product available in 2007.

Require Q (rimsulfuron + dicamba) and Resolve Q (rimsulfuron + thifensulfuron) are new premix products for postemergence applications in corn. Each product contains a safener to reduce the potential for corn injury and can be tankmixed with glyphosate for use in glyphosate-resistant corn hybrids. Require Q is applied at 4 ounces per acre and Resolve Q at 1.25 ounces per acre. Application timings vary according to corn stage and by product. Resolve Q can be applied to corn that is up to 20 inches tall but should not be applied to corn exhibiting 7 or more leaf collars. Require Q can be applied any time after corn has reached 4 inches in height (V2) and before it exceeds 20 inches tall or exhibits 7 or more leaf collars.

Rage D-Tech 6.05EC (carfentrazone + 2,4-D ester) can be used for burndown control of existing vegetation prior to corn or soybean planting. The label lists required intervals that must elapse between preplant application and crop planting. Rage D-Tech can also be applied postemergence to corn from spiking until corn is 8 inches tall.--Aaron Hager

Aaron Hager

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