Burndown Strategies With The Calendar Running Out and Crop Mix in Question

JACKSON, TENN.
   This spring has been almost 180 degrees different from last spring. The dry spring of 2012 allowed a lot of early field work and at this time we were in the middle of corn planting. This spring we are way behind on applying burndowns due to all the wet weather. With the crunch to get burndowns out there have been a lot of calls on how best to proceed burning down particularly now with some looking to adjust their crop mix from corn to more cotton.
   This spring with all the cold weather marestail is just starting to green back up. That marestail is still small and makes it easier to control than it was this time last year and gives us some good options. Glyphosate mixed with either Dicamba, 2,4-D or Sharpen would all be good choices here regardless of what crop is to be planted. Glyphosate mixed with Verdict would be a good choice if the field is to be planted to corn or soybean. As the marestail begins to bolt over the next week to 10 days then higher rates of the products mentioned above should be utilized. Another good option would be a tankmix of Sharpen + pt of 2,4-D on large marestail.
   The next question that comes up is if a residual herbicide should go into the mix and if so which one? There is no across the board answer to this question. The answer depends upon two main things. First, what crop is expected to be planted? If the field is to go to corn and the field is expected to be planted around April 1 then a residual may not be needed. If your corn program is a planned two pass (which is the most consistent way to go) then a qt of atrazine or simazine with crop oil or Gramoxone will allow a clean start.
   Second, what is the expected time frame of planting? If the field is slated to go to soybean or cotton and may not be planted for 4 to 6 weeks then some kind of residual makes sense. The two most common are Valor or Leadoff. Both will do a good job providing residual control on winter annual weeds like horseweed. However, if Palmer amaranth is the main concern then Valor would be the best fit. Please note if you plan to use the new premix of Fierce which contains Valor and pyroxasulfone, that only 3 ozs of Valor can be utilized in soybean. If Fierce is to be used then in most cases Leadoff or another residual herbicide at burndown would be the way to go. Please also note that the plant back to cotton or soybean after a 1.5 oz/A Leadoff application is 30 days. Δ
   DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee