By Mark Loux, Ohio State University Extension herbicide specialist
There are some changes with regard to Pyroxasulfone herbicides that growers should be aware of in the coming year. Here is an overview.
Pyroxasulfone is a new active ingredient for residual control of annual grasses and certain small-seeded broadleaf weeds. It can be found in several products that were recently labeled for use in corn, and several of these will be labeled for use in soybeans in the near future as well. Mode of action of pyroxasulfone is similar to the acetamides — a group 15 seedling growth inhibitor. Pyroxasulfone controls most annual grasses, pigweed, waterhemp, lambsquarters, and black nightshade, and also has fair activity on common ragweed and velvetleaf at higher rates. The spectrum and length of control is dependent upon rate, as with most herbicides.
The premix products that contain pyroxasulfone are geared for use in a planned preemergence followed by postemergence program. The lower pyroxasulfone rate in these products is generally not intended to provide full-season weed control, and also results in reduced control of some broadleaf weeds. Several companies have access to pyroxasulfone, but it appears that some can sell it only as a premix product, while others can sell it as a stand-alone product. The pyroxasulfone products and uses that are approved at this time are listed below.
Anthem (FMC) is a premix of pyroxasulfone and fluthiacet-methyl (Cadet) for preplant/preemergence use on corn. Fluthiacet does not provide residual weed control, so the spectrum of control is due to pyroxasulfone alone (identical to Zidua). Anthem ATZ, a premix of pyroxasulfone, atrazine, and fluthiacet, should be registered in the near future. We had not seen a label for either product at the time that this was written.
Fierce (Valent) is a premix of pyroxasulfone and flumioxazin (Valor) for preplant use in field corn. Similar to the Valor label, Fierce has to be applied at least seven days before corn planting, and can only be used in no-tillage conditions. This product controls annual grasses, pigweeds, waterhemp, lambsquarters, velvetleaf, smartweeds, and black nightshade, and controls/suppresses common ragweed. Fierce should be available for use in soybeans in the near future, along with Fierce XLT, which is essentially a premix of pyroxasulfone and Valor XLT.
Zidua (BASF), pyroxasulfone, is labeled for preplant or preemergence use in all types of corn — field, seed, sweet, and popcorn. Zidua should generally be mixed with another herbicide that has broadleaf activity regardless of whether it is a preemergence or preemergence plus postemergence program. Zidua can also be applied early postemergence, but should be mixed with other herbicides that control emerged weeds.