Corn and Soybean Herbicide Updates

Chris Boerboom, Ext. Weed Scientist

Corn

Autumn (Bayer) is a herbicide targeted for fall burndown applications for broadleaf weed control before field corn.  Spring burndown applications are also labeled, but they must be made 30 days before planting corn, which would prevent this as a practical option.  Autumn is a 10% dry formulation of iodosulfuron, which is an ALS inhibitor.  The labeled rate is 0.3 oz/a Autumn with crop oil concentrate at 1% plus either 1.5-2 qt/a UAN or 1.5-3 lb/a AMS.  Several of the key weeds on the label that would be important in Wisconsin include alfalfa, dandelion, horseweed, and mustards among others.  Tank mixtures with either 2,4-D at 1 pt/a or glyphosate would be likely options depending on the weed spectrum. 

Status (BASF) is a dry premix of 40% dicamba and 16% diflufenzopyr (same ingredients and ratio as Distinct) plus isoxadifen.  Isoxadifen is the safener that is also used in Option.  Status can be applied postemergence to control many broadleaf weeds in field and seed corn.  The spectrum of control will be similar to Distinct since the active ingredients are the same.  However, the safener will lessen the risk of injury compared to Distinct, which might be a concern to some people, especially with applications to taller corn or when high temperatures favor rapid corn growth.  While Status increases corn’s tolerance, care should still be used with Status in cleaning out spray tanks and avoiding drift conditions because Status contains dicamba.   

Status can be applied at 5 to 10 oz/a to 4- (V2) to 36-inch (V10) tall corn.  Nonionic surfactant (0.25%), crop oil (0.5-1%), or methylated seed oil (0.5-1%) plus UAN or AMS are recommended adjuvants.  Status can also be tank mixed with glyphosate, Liberty, or Lightning at rates starting at 2.5 oz/a. A 5 oz/a rate of Status contains an equivalent rate of dicamba and diflufenzopyr as a 4 oz/a rate of Distinct.

Soybean

Canopy (DuPont) is now registered for use in Wisconsin.  It had been registered for use in states to our south for several years, but was not registered for use in Wisconsin because of concerns of carryover injury to corn.  Canopy contains the ingredients in Classic (chlorimuron) and Sencor (metribuzin), which will provide burndown and residual broadleaf and foxtail control.  It can be applied from 45 days before planting to preemergence after planting soybean.  Only the lowest rate of 2.25 oz/a can be used in Wisconsin and it can only be used south of I-90 west of Madison and south of I-94 east of Madison.  The 2.25 oz/a rate contains the equivalent of 1 oz/a Classic and 1.9 oz/a Sencor.

Authority First DF (FMC) and Sonic (Dow) are identical premixtures of the ingredients in Spartan (sulfentrazone) and FirstRate (cloransulam).  A rate comparison is shown in the next table.  These premixtures should be applied from preplant to 3 days after planting and will provide residual control a range of broadleaf weeds including lambsquarters, nightshade, pigweeds, common and giant ragweed, and velvetleaf.  The labeled rate ranges from 6.45 to 8 oz/a, but reduced rates would provide early season weed control of broadleaf weeds in glyphosate-resistant soybeans.  Potato, sweet corn, and snap beans cannot be planted the year after applying these premixes.

Prefix CP  is a co-pack of Dual Magnum and the two products in the pack are labeled as Prefix (the Dual Magnum component) and Reflex.  A true premix of these herbicides will be marketed in the future.  This preemergence mixture will provide residual grass and broadleaf weed control.  The standard rates will be 1 pt/a of each product, which will provide early season weed control and could be followed by a postemergence herbicide for season long control.