Tips for early herbicide application
The warm and relatively dry weather has many growers chomping at the bit to apply herbicides now, whereas this might have been more likely to occur in several weeks in a more typical spring weather pattern. It probably makes sense to apply burndown herbicides now in many no-till fields based on the size of the weeds that are present. Vegetation in no-till fields is larger than usual for this time of the year due to the warm weather, and lack of fall herbicide application in all but a few fields. Waiting several weeks to apply herbicides will only result in an even more challenging burndown situation. It can make sense to apply burndown herbicides now even where a field will be tilled later, in fields where there is enough vegetation to interfere with spring seedbed preparation.
This is probably the ideal situation for the use of the higher rates of 2,4-D ester in burndown treatments. We have been encouraging use of the higher rates to improve control of marestail, which is fairly advanced in rosette size in some fields already. A reminder that any 2,4-D ester product can be applied 7 days before planting at rates up to 0.5 lb ai/A. There are several products that can be applied 15 days before planting at rates up to 1 lb ai/A (e.g. Weedone 650, E99, Salvo), but otherwise the higher rates require 30 days. Treating fields now with the 1 lb rate of 2,4-D ester (with glyphosate or other burndown herbicides), with the intention of planting in two weeks or so, can improve control of larger, older weeds. As we move closer to planting, or in especially weedy fields, the addition of Sharpen to glyphosate/2,4-D mixtures can improve control. The addition of products containing chlorimuron (Canopy/Cloak, Valor XLT, Envive, Authority XL) can also improve burndown of some no-till weeds.
One caution about burndown herbicides, especially in a year when weeds are more numerous and larger than usual. We have previously mentioned the alternatives to glyphosate/2,4-D for burndown of marestail, which include Liberty/metribuzin and glyphosate/Sharpen. While the latter two mixtures are effective for burndown of marestail and a number of other weeds, they can struggle some in a situation where the full complement of large no-till weeds is present (they typically work well in fields that have received a fall herbicide application).
Glyphosate/2,4-D still has the lowest cost and most utility across a range of no-till burndown situations, and switching to a mixture that does not include 2,4-D should generally occur only where necessary and where the weed spectrum fits the alternative mixtures. Optimum activity from mixtures that contain Sharpen, Liberty or Gramoxone will occur with spray volumes of at least 15 gpa and the appropriate nozzles.