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Valor Registered for Soybeans

April 20, 2001
Valor 51WDG (flumioxazin) recently received a label for use in soybeans. The active ingredient belongs to the N-phenylphthalimide herbicide family and controls susceptible species by inhibiting the PPO enzyme of the chlorophyll biosynthesis pathway. Valor may be applied at 1 to 3 ounces per acre, as a burndown alone or tank-mixed with other herbicides, or at 2 to 3 ounces per acre, as a preemergence treatment. Include a crop oil concentrate, methylated seed oil, or nonionic surfactant when using Valor as a burndown treatment. A spray grade nitrogen source may also be included. Do not incorporate Valor into the soil after application. Valor may also be applied before, during, or after planting but before soybean emergence. Application after soybeans emerge will result in severe crop injury. Do not use Valor in soybean fields where products containing flufenacet (Axiom, Domain), alachlor (Lasso, Micro-Tech), metolachlor (Dual II Magnum), or dimethenamid (Frontier, Outlook) will be used, as soybean injury may occur.

Valor has better activity on small-seeded broadleaf weed species than against large-seeded broadleaf species. Table 1 contains Valor efficacy ratings on various broadleaf weed species. The mode of action of Valor is similar to the herbicide Authority (sulfentrazone), and the two herbicides have very similar weed control spectrums. Research at the University of Illinois and other Midwest universities has compared these two herbicides for weed control performance and soybean tolerance.

Since these two herbicides are so similar with respect to their weed control spectrum and activity, what are some of the differences between these two herbicides? Comparisons have shown that Authority may provide longer soil residual weed control than Valor. This has been apparent in a number of trials that have been conducted at the University of Illinois. This may not be a particular concern in planning weed control strategies since both of these herbicides will most likely be used as a foundation herbicide in a sequential herbicide program. The half-life of these herbicides may account for their differences in persistence; Valor's soil half-life ranges from approximately 12 to 18 days, while Authority's soil half-life is 100 to 280 days.

Soybean tolerance to Valor and Authority is another area where research at the University of Illinois has shown some differences. Greenhouse and field research conducted by Taylor-Lovell, Wax, and Nelson indicated Valor is less injurious to soybeans than Authority. Soybean tolerance in these studies was directly related to differences in soybean variety and environmental conditions. Even though differences in soybean tolerance were evident with both herbicides based on soybean variety, differences among varieties were more apparent with Authority than with Valor. From this research they also found that differences in soybean varieties with one herbicide may be unrelated to the other, suggesting that a thorough screening of soybean varieties may need to be done with both herbicides to determine soybean tolerance based on variety. In all cases, soybean yield was not reduced with labeled rates of Valor. Environmental conditions that equated to greater soybean injury with Valor and Authority were cooler temperatures and significant amounts of rainfall after soybean planting.--Christy Sprague and Aaron Hager

Author: Aaron Hager Christy Sprague

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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