Cotton Injury From Post-Applied Dual Magnum And Warrant

DR. LARRY STECKEL

JACKSON, TENN.
   A lot of reports of cotton injury from post applied Dual Mag or Warrant over the past several days. This is not unusual as we have this issues to some degree every year.Despite being a common issue for most springs it is somewhat hard to predict how much a problem it will be for any given year as so much depends upon the environment.
   This year injury from these herbicides seems to be more widespread of a problem as many acres received one or the other of those herbicides during a warm week with a lot of humidity which really increases injury from these herbicides. What made matters worse is that the cotton had very thin cuticles at time of application which makes them more susceptible to injury. Moreover some cotton had also suffered sand-blasting which can increase the injury from those herbicides.
   In walking some of these fields it appears that the cotton is recovering. Going by past history this is also what I would expect. However, we would like to avoid this injury for the rest of the year and below are some tips to help reduce injury from these post applications:
   If possible wait for soil to dry as wet soil can increase burn from Dual Magnum or Warrant due to the increase in humidity.
   Use larger droplet size nozzles (TTI, AIXR, AI, TDXL, TADF, etc) and reduce the gallons per acre to 10 or less. This decreases the coverage and lessons the area of the leaf that will be injured.
   Do not let the agitation shut down even for a few minutes and then start to spray. Dual and Warrant will readily settle out without agitation and the next acres will get a high rate of those causing excessive burn.
   If spray load sits overnight be sure to agitate load for 10 to 12 minutes then spray for several minutes before spraying field.
   Of course many of these applications go out tankmixed with acephate, glyphosate and/or Liberty. Scott Stewart and I have several years of research with acephate tankmixed with all of these combinations and have never found that adding that insecticide increases injury. With thrips more of an issue in recent years it makes sense to add acephate.
   The addition of glyphosate with either Dual Magnum or Warrant can heat up the burn a little depending upon the surfactant in the glyphosate used. Typically this increased injury is not much more than what you can get with either Warrant or Dual Magnum alone.
   Liberty is loaded with surfactant as well and this can also heat up the injury if tankmixed with Dual Magnum or Warrant. On the true Liberty Link cotton the injury is typically not a major issue and the added residual is a good practice. However, on cotton with moderate glufosinate tolerance injury can be excessive. It is best to apply the Warrant or Dual Magnum with a separate application over those cotton varieties. ∆
   DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee
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