Jeffrey L. Gunsolus, Extension Agronomist - Weed science
On June 8, 2018 the Minnesota Commissioner of Agriculture released a letter to stakeholders indicating that the MDA will be keeping the 24(c) restrictions for XtendiMax, Engenia and FeXapan in place for 2018. The Commissioner’s letter also explains the rational for holding to the 24(c) restrictions, despite the challenges presented by late planting dates for soybean in many parts of the state.
Please note that with the increase in temperature and good to excessive soil moisture, key target weed species such as common lambsquarters and common and giant ragweed are rapidly growing and herbicide applications will be most effective on weeds less than 4 inches tall. Also, dicamba is less effective on tall waterhemp because tall waterhemp is a late emerging summer annual with a long duration emergence period that extends well into July. Dicamba does not have effective soil residual activity to control tall waterhemp emergence into July.
A primary purpose for the Xtend technology is to help manage the multiple herbicide resistance issues found in common and giant ragweed, tall waterhemp and kochia. As early season weed control options diminish, poor control due to late applications of dicamba has the potential to advance the rate of selecting for resistance to dicamba. This would defeat a primary purpose of this technology.
Rationale for keeping the 24(c) restrictions
Please keep in mind that if the 24(c) restrictions were removed then the default growth stage would be through the R1 growth stage but before the R2 growth stage. Due to the wide range of soybean planting dates, it is likely that many soybeans will not enter the R2 growth stage until July. In 2017, 50% of the dicamba-related injuries reported to the MDA occurred at or after July 2nd and 75% of the dicamba-related injuries occurred after June 21st. The sheer volume of dicamba-related injuries reported after June 20th last year support the rationale for this cutoff date.Please note that with the increase in temperature and good to excessive soil moisture, key target weed species such as common lambsquarters and common and giant ragweed are rapidly growing and herbicide applications will be most effective on weeds less than 4 inches tall. Also, dicamba is less effective on tall waterhemp because tall waterhemp is a late emerging summer annual with a long duration emergence period that extends well into July. Dicamba does not have effective soil residual activity to control tall waterhemp emergence into July.
A primary purpose for the Xtend technology is to help manage the multiple herbicide resistance issues found in common and giant ragweed, tall waterhemp and kochia. As early season weed control options diminish, poor control due to late applications of dicamba has the potential to advance the rate of selecting for resistance to dicamba. This would defeat a primary purpose of this technology.
Federal label restrictions
This article has focused solely on the 24(c) restrictions, yet the Federal label has many other challenging restrictions on wind speed, adjacent sensitive crops, and inversions that must be addressed as the June 20th cutoff date approaches. Please be considerate of your applicators’ concerns as it is the applicator who is ultimately the responsible party if off-target injury issues occur.