"In corn, when applying burndown herbicide treatments, there is concern regarding any cold, wet soil stress and any cracked open seed trenches we may see if we have a tough spring," says McGrath. "Try to avoid applying 2,4-D under these conditions if there is potential of a rain driving acetanilide (or other residual herbicides for that matter) and 2,4-D into the seed zone soon before and/or after planting, as this can cause seedling damage. With the price of glyphosate being low, glyphosate herbicide would be a great substitute in with an atrazine premix rather than 2,4-D if there is a weather driven risk of corn injury."
If a weed is not growing actively, there is greater risk that a burndown herbicide treatment won't work as well as it usually does
Bottom line on all of this: If a plant is not growing actively, there is a greater risk that the burndown won't work as well as planned. "Sometimes to get the majority of early weeds taken out before the crop is up, we have to compromise, so don't hold your dealer's feet to the fire if your burndown misses a few weeds," says McGrath. "Follow your local dealer's best recommendations. They will be working with chemical company reps for specific ideas on burndown herbicide treatments and how to use them."
A couple other key thoughts on the subject of using burndown herbicides
* Use plenty of adjuvants/additives such as Concentrated Oil Concentrates, or COCs, Nonionic Surfactants, or NIS, and Ammonium Sulfate, or AMS surfactants -- whatever your dealer recommends for the tank mix, be generous with the amounts, especially if the weather is tough, like cold nights or drought stress.
* If the wind will cooperate, flat fan nozzles (like XRs) do a better job on tough weeds than AIs or TTs in general.
* "We often add more NIS and sometimes some COC to our glyphosate even if it is already a "loaded" product," says McGrath. "Local experience and many of our local agronomists tell us this helps get more consistent weed control."