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 (December) 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 7 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.
Major changes here include two new mesotrione premixes from DuPont, and some reformulating and renaming of Syngenta products. Lexar and Lumax have been subject to minor reformulating, and are now Lexar EZ and Lumax EZ. Camix, the premix of mesotrione and s-metolachlor, has been renamed Zemax. New Dupont mesotrione products include the following:
Instigate, a mixture of mesotrione and rimsulfuron, is labeled for preplant, preemergence, and early postemergence use in field corn. Instigate provides residual control or suppression of annual grass and broadleaf weeds, and has activity on emerged weeds. Application of this product alone will generally not be adequate in either a total preeemergence or preemergence followed by postemergence herbicide program. A mixture of Instigate plus an atrazine premix should have burndown activity that is similar to Lexar and Lumax, as well as similar residual weed control. Can be applied postemergence through the 2-collar corn stage, and should be mixed with COC or MSO plus UAN or AMS when used for control of emerged weeds. Interactions between this product and soil-applied insecticides can result in corn injury – check the label for restrictions.
Realm Q, a mixture of mesotrione and rimsulfuron, is labeled for postemergence use in field corn. This product contains isoxadifen, a safener that reduces the risk of crop injury. Realm Q can be applied up to 20-inch corn and prior to the 7-collar stage. Controls small grass (less than 2 inches) and broadleaf weeds, but should generally be mixed with glyphosate, Liberty, or another herbicide for broad-spectrum postemergence control. Preferred adjuvant system is COC or MSO plus UAN or AMS, although NIS can be substituted for COC/MSO. Additional NIS is not needed when mixing with a loaded glyphosate product. Interactions between this product and soil-applied insecticides can result in corn injury – check the label for restrictions.
Soybean Herbicide premixes
Intimidator (Loveland/CPS) is a premix of s-metolachlor, fomesafen (Reflex), and metribuzin for preplant or preemergence use in soybeans. Activity is similar to a mixture of Prefix plus metribuzin. Intimidator provides broad-spectrum weed control but will be generally less effective for residual control of giant ragweed compared with other broad-spectrum soybean herbicides (Valor XLT, Gangster, Sonic, Authority XL, etc). The addition of a few ounces of metribuzin 75DF will improve marestail control, especially where the lower rates of Intimidator are used.
Matador (Loveland/CPS) is a premix of metolachlor, imazethapyr (Pursuit), and metribuzin for preplant or preemergence use in soybeans. A use rate of 2 pints/A would be typical in a planned preemergence followed by postemergence soybean herbicide program. This rate provides the equivalent of 1 lb ai/A of metolachlor, 3 oz/A of metribuzin 75DF, and 2 oz/A of Pursuit 2L. Matador provides broad-spectrum weed control but will generally less effective for residual control of ragweeds and marestail compared with other broad-spectrum soybean herbicides (Valor XLT, Gangster, Sonic, Authority XL, etc). Mixing this product with additional metribuzin 75DF will improve residual marestail control, and also burndown of some weeds.
Major changes with saflufenacil products within the past year or so include the addition of higher soybean burndown rates and planting restrictions, and one new product. Sharpen can now be applied at rates up to 2 oz/A in soybean burndown programs, and higher rates can improve burndown and residual broadleaf weed control. As Sharpen rates increase above 1 oz/A, the minimum interval between application and soybean planting increases. For soils with more than 2% organic matter, the minimum delay between Sharpen application and planting: 1 oz – anytime before emergence; 1.5 oz – 14 days; 2 oz – 30 days. Similar changes have occurred for Verdict use rates in soybeans. The 5 oz Verdict rate can be applied anytime before crop emergence, while rates of 7.5 and 10 oz/A must be applied 14 and 30 days before planting, respectively. On soils with 2% or less organic matter, the minimum interval between Sharpen or Verdict application and planting is 30 or 44 days even at lower rates.
Optill PRO, which is a copack of Optill plus Outook. The use rate of the copack provides the equivalent of 2 oz of Optill and 10 oz of Outlook per acre. The addition of Outlook improves control of annual grasses, pigweeds, waterhemp, and black nightshade. Outlook PRO can be applied anytime prior to cracking, or soybean emergence.
There have been some changes in the status of the labels for mixing saflufenacil products with other PPO-inhibiting herbicides since last spring. Labels in effect currently state that saflufenacil cannot be mixed with the following herbicides: flumioxazin (Valor, Valor XLT, Envive, Enlite, Gangster, Fierce); or fomesafen (Prefix, Intimidator). In addition to the prohibition of mixing, a period of 30 days must separate the application of any of these and the application of saflufenacil. Several products containing sulfentrazone can still be mixed with saflufenacil, and these include: Sonic, Authority First, and Authority XL.