Weed Control Management In Conventional Soybean

DR. LARRY STECKEL

JACKSON, TENN.
   There have been a number of calls this spring on weed control in conventional soybean. This is not new as calls on weed control in conventional soybeans have been more frequent the last two years. Typically the weed spectrum that is the main issue with these calls is not Palmer amaranth but cocklebur and sicklepod. 
   The reason cocklebur and sicklepod are the main weeds in question is that most design their weed management to control Palmer amaranth. They utilize overlapping residuals with herbicides that are effective on Palmer amaranth. These herbicides often are not effective on large seeded broadleaf weeds like sicklepod and cocklebur. Roundup or Liberty in RR or LL soybeans are very effective on sicklepod and cocklebur which of course is not an option in conventional soybean.
   The majority of the cocklebur in our state is ALS-resistant so metribuzin PRE followed by Storm or Reflex early POST are the best herbicide options.  Sicklepod is not ALS-resistant, though Scepter and Pursuit were never very effective on it. According to research by Dr. Bob Hayes, Classic and FirstRate are both good options for sicklepod applied either PRE or POST. Classic or FirstRate are often added in premixes with our main Palmer herbicides like Valor and Authority. If you go the premix route, be sure to follow the label and go with the higher use rates for the given soil type to be sure to have enough Classic or FirstRate to provide consistent control. As with all PRE applied herbicides, control may not be adequate and an early post application of Classic or FirstRate may be needed. ∆
   DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee