Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
The last week of weather has led to some soybean fields with no preemergence herbicides applied. Fields planted but without preemergence herbicides have few options available. Soybeans with herbicide-traits of Roundup, Liberty or Xtend can be sprayed after emergence, but whether to include a residual herbicide is a difficult decision. Products containing metribuzin, sulfentrazone (Authority products), or flumioxazin (Valor, Fierce, Envive) will severely injured emerged soybeans, or even soybeans that have started to crack the soil surface. The Group 15 herbicides, Dual, Warrant, Zidua can be applied to emerged soybeans for residual control, but they will not control emerged weeds. Most of the postemergence herbicides need the soybeans to have 1 to 2 trifoliate leaves before application, so be sure to read the label for application timings.
In no-till fields, be sure the weeds are dead before planting. Once soybeans are planted herbicide options become more limited. In fields with glyphosate-resistant common ragweed, be sure you have an effective herbicide to control these herbicide-resistant weeds. Options include 2,4-D, dicamba (Xtendimax soybeans), or paraquat plus metribuzin.