Double Crop Burndown Strategy

JACKSON, TENN.
   Wheat harvest is in full gear and yield reports have been very good. This of course has led to a number of questions on double crop burndown strategy. The answer to these question hinges on two questions that I always ask. First, what is the weed spectrum in the harvested wheat field? Second, will the soybeans planted in the field be Liberty Link (LL) or Roundup Ready (RR)?
   If the weed spectrum in the field consists of a significant population of horseweed or giant ragweed then Liberty tankmixed with metribuzin would be a very effective choice. However, if the field has a good stand of Palmer amaranth then Gramoxone tankmixed with metribuzin would probably be the best choice even if horseweed is present. The reason I say this is that I am more concerned about Palmer amaranth in the double crop soybeans than horseweed.
   I often recommend metribuzin in the double crop burndown situation. The reason for this is that metribuzin will improve the weed control of both Gramoxone and Liberty. Moreover, metribuzin can provide effective and economical residual control of Palmer amaranth. I have had some folks ask about using Verdict or Sharpen for horseweed burndown after wheat harvest. Unfortunately, I really do not have any research on how these herbicides perform on horseweed that has been cut off during wheat harvest.
   The second question on whether the soybeans will be LL or RR also plays a role on what burndown to utilize. If the field will be planted to LL soybeans then I would not use Liberty as a burndown and just go with it early post emergence, probably tankmixed with Dual or Warrant. If the field is to go to RR soybeans, then Liberty in the burndown would be a good fit if horseweed is present in big numbers.  However, if the horseweed population is spotty and/or there is a good deal of Palmer amaranth, then Gramoxone would be the best option. Then in crop be sure to tankmix say a Prefix in with the first application of glyphosate. Also, FirstRate in RR soybeans can help suppress any horseweed cripples that survive the Gramoxone burndown. ∆
DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee