Palmer Amaranth Management In 2016
DR. LARRY STECKEL
JACKSON, TENN.
There has been some discussion about how to manage Palmer amaranth next year in light of the likely PPO-resistant Palmer amaranth in the picture in some fields. Utilizing Liberty Link soybeans is a good option but seed supply in my mind is a question. The Roundup Xtend and/or Enlist soybeans could be another option but I do not count on them until we have the label in hand and again seed supply is a question.
At this point, I think we need to plan for next year like the tools we have now are what we will have available on significant acres next year. With that in mind, I talked to several of my colleagues from the Midwest this morning where this PPO-resistant waterhemp has been a fact of life for over a decade now to see how they have managed it. First they have not gotten away from using herbicides like Prefix or Envive. They still get good residual control from those products. Moreover they can control PPO-resistant waterhemp even POST with a pint of Flexstar up to about 2” tall. Prior to the resistance development they were often controlling waterhemp up to 6” tall.
Seeing how the resistance seems to be the same in our Palmer amaranth as in waterhemp I think we can assume that PRE applied PPO herbicides should provide a similar level of residual control between the PPO resistant and susceptible Palmer. From a POST applied perspective judging from the fields I have walked as well as reading the literature on how the waterhemp is managed, I still believe a quart of Prefix will control the PPO-resistant Palmer amaranth from emergence up to about 1” tall. We plan to do some greenhouse work to see if this is the case. However, I would expect very sketchy control of 2 to 3” tall Palmer amaranth with a post applied PPO herbicide.
We need a program approach. The field must start clean. We then need to use a PRE Plant or PRE applied premix or tankmix that contains two effective Palmer amaranth herbicides followed 14 days later with Prefix or Dual Magnum or Zidua/Anthem POST emergence would be a good plan. In other words, overlay residuals and do not allow the Palmer to emerge is plan A. If the Palmer amaranth does emerge then plan B is to spray it before it gets an 1” tall. Herbicides to go with here would be Prefix spiked with more Flexstar or Ultra Blazer or Cobra if it is borderline too large.
Some good premixes in no certain order would be Boundary (Dual Magnum + metribuzin), Trivence (Dual Magnum + metribuzin + Valor), Authority Elite/BroadAxe (Sulfentrazon + Dual Magnum), Intimidator (Dual Magnum + metribuzin + Reflex), Verdict (Sharpen + Outlook) and Fierce (Valor + Zidua). Another option would be to make your own tankmix like Envive plus Zidua.
Consider going with higher rates of PRE applied herbicides. Check the label but many of the more popular premixes can be spiked with more active ingredient. If the soil type allows spike Dual Magnum up to 1.5 pts, Zidua up to 2.5 ozs, Outlook up to 18 ozs and metribuzin up to 1/3 of a lb would be a good rates to target. ∆
DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee