Dicamba Use and Considerations on PrePlant Soybeans

As we look ahead to another cropping season, soybean growers need to have a plan to control marestail.  Best practice management for soybeans includes a fall burn down followed by an early spring burn down to allow the field to begin marestail free.  In fields not treated with a burn down herbicide last fall, dicamba is a good spring burn down option.  Work by Mark Loux, OSU Extension weed specialist, and his lab, has shown dicamba to be the most effective burn down herbicide on glyphosate-resistant marestail in the spring, usually killing or at least stopping emerged marestail in their tracks without help from other herbicides. 

The issue with dicamba use in the spring has typically been that label restrictions make it difficult to use in a timely manner.  For example, the label on the dicamba product Clarity says “Following application of Clarity and a minimum accumulation of one inch rainfall or overhead irrigation, a waiting period of 14 days is required for 8 fluid ounces/acre or less, and 28 days for 16 fluid ounces/acre.  These intervals must be observed prior to soybean planting or crop injury may occur.”  Note that the 14-day waiting period begins after an inch of rain has accumulated following the application, not after the application itself.  With the new dicamba products and technology, soybean growers now have another, less restrictive, option for preplant dicamba application as a spring burn down.

Mark Loux, in a recent OSU Extension Ag crops team newsletter outlined that less restrictive option.  For growers who are using Xtend soybeans, “ …it is possible to apply the approved dicamba products, Engenia, XtendiMax, or FeXapan, any time prior to planting without a waiting period regardless of product rate (within the specified range), and then also at or after planting as well. These are the only three dicamba products that are approved for this less restrictive type of use. Since the use is specific to these products and Xtend soybeans, the user is required to consult the individual product labels and websites for approved tank mixes, nozzles, etc. Furthermore, all of the stewardship guidelines and restrictions on application listed on labels and covered in the dicamba training sessions apply here. Tank mix options are generally not as numerous, since every individual tank mix partner must be on the approved list.”