Below are brief descriptions of herbicides introduced over the past year or so. As readers are undoubtedly aware, there is currently almost no development of new active ingredients. Most of the products mentioned here are premixes of existing herbicides. Some of these seem to have a fit for Ohio situations while others do not. A brief Powerpoint video on this is covered here: http://agcrops.osu.edu/specialists/weeds.
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 labeled for pre-plant/pre-emergence use in corn and soybeans over the past year or so. It can also be applied early post-emergence in corn, but only for residual control of later-emerging weeds, not control of emerged weeds. Mode of action of pyroxasulfone is similar to the acetamides — a group 15 seedling growth inhibitor.
Pyroxasulfone controls most annual grasses, pigweed, waterhemp, Palmer amaranth, 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 pre-emergence followed by a post-emergence 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 currently available pyroxasulfone products and uses are listed below.
Zidua (BASF), pyroxasulfone, is labeled for pre-plant or pre-emergence use in soybeans and 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 pre-emergence or pre-emergence plus post-emergence program. Zidua can also be applied early post-emergence, but should be mixed with other herbicides that control emerged weeds.
Anthem (FMC) is a premix of pyroxasulfone and fluthiacet-methyl (Cadet) for pre-plant/pre-emergence/early post-emergence use in corn. Fluthiacet does not provide residual weed control, so the spectrum of control is due to pyroxasulfone alone (identical to Zidua). Anthem ATZ is a premix of pyroxasulfone, atrazine, and fluthiacet. Both products can be used in any type of corn.
Fierce (Valent) is a premix of pyroxasulfone and flumioxazin (Valor) for pre-plant use in field corn, and pre-plant/pre-emergence use in soybeans. 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. It can be applied pre-plant or no later than three days after soybean planting, and prior to crop emergence. This product controls annual grasses, pigweeds, waterhemp, lambsquarters, velvetleaf, marestail, smartweeds, and black nightshade, and controls/suppresses common ragweed.
Control of marestail is from the flumioxazin alone, so control of this weed is not improved with Fierce compared with Valor. The same can be said for most of these other broadleaf weeds as well, since Valor already has substantial activity on most of them, and so the pyroxasulfone ends up contributing primarily grass control. Fierce can be more effective for residual control of waterhemp and Palmer amaranth compared with Valor. Fierce XLT should be available for use in soybeans in the near future, and is essentially a premix of pyroxasulfone and Valor XLT.
Corn and Soybean Premixes
Callisto GT (Syngenta) is a premix of mesotrione (Callisto) and glyphosate for post-emergence use in glyphosate-resistant corn. It can be applied until corn is 30 inches tall or the V8 stage, whichever occurs first.
Authority MAXX (FMC) is a premix of chlorimuron (Classic) and sulfentrazone (Spartan/Authority) for pre-plant/pre-emergence use in soybeans. The ratio of sulfentrazone to chlorimuron is higher in this product compared with Authority XL, but the spectrum of control and other characteristics are similar between the two products. Due to the lower rate of chlorimuron in Authority MAXX, the crop rotation restrictions are not pH-dependent, which differs from most other chlorimuron products.
Intimidator (Loveland/CPS) is a premix of s-metolachlor, fomesafen (Reflex), and metribuzin for pre-plant or pre-emergence 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 where the lower rates of Intimidator are used.
Marvel (FMC) is a premix of fomesafen (Reflex) and fluthiacet (Cadet) for post-emergence use in soybeans. The rate of fomesafen is fairly low in this product and the spectrum of control for fluthiacet is narrow. The 7.25 oz rate contains the equivalent of 10 oz of Reflex and 1 oz of Cadet. Marvel is apparently intended for use in mixtures with glyphosate in Roundup Ready soybeans to help control glyphosate-resistant weeds, primarily glyphosate-resistant Amaranthus species. This product has no activity on marestail.
Matador (Loveland/CPS) is a premix of metolachlor, imazethapyr (Pursuit), and metribuzin for pre-plant or pre-emergence use in soybeans. A use rate of 2 pints/A would be typical in a planned pre-emergence followed by post-emergence 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.
Pummel (MANA) is a premix of metolachlor and imazethapyr (Pursuit) for residual control of weeds in soybeans. It is generally intended for pre-plant/pre-emergence use but can also be applied early post-emergence. This product may have limited fit in Ohio since it provides little to no control of marestail, and post-emergence activity is due to an ALS-inhibiting herbicide. When used pre-plant/pre-emergence, Pummel should be mixed with metribuzin to ensure residual marestail control.
Torment (MANA) is a premix of imazethapyr (Pursuit) and fomesafen (Reflex) for pre-plant, pre-emergence or post-emergence use in soybeans. This product provides little to no control of marestail pre-emergence, and none post-emergence. Spectrum of control is otherwise fairly broad, but this product may be most appropriate for the management of glyphosate-resistant Amaranthus species.
Labels for all saflufenacil products, Sharpen, Verdict, and Optill PRO, currently still prohibit mixtures with other PPO-inhibiting herbicides — flumioxazin (Valor, Envive/Enlite, Gangster, Fierce), sulfentrazone (Authority products, Sonic), and fomesafen (Prefix, Vise, Torment). Applications of saflufenacil should be separated from application of the other PPO inhibitors by at least 30 days.
The other major change for Sharpen and Verdict has been the addition of higher rates in soybeans. The higher rates have improved the length of residual marestail control in OSU research, even with the labeled waiting period between application and planting for these rates. Sharpen can now be applied at rates up to 2 oz/A in soybean burndown programs. 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.