Wheat harvest is moving along briskly, and in many Southern states yields are good, especially in Tennessee. Many growers look to follow the harvest with soybeans, either Liberty Link or Roundup Ready, but they need a good burndown and weed strategy to make it profitable.
In a June 19 blog, Larry Steckel, University of Tennessee Extension weed specialist, talks about both soybean flavors and the best way to knock weeds down to give soybeans a help up this year. First he asks a few questions:
What is the weed spectrum in the harvested wheat field? And second, will the soybeans planted in the field be Liberty Link or Roundup Ready?
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.