Which weeds are already present when you’re planning a burndown? Which weeds will most likely emerge later even if you have a clean field after spraying last fall?
These are questions Bill Johnson suggests asking to put together effective weed control strategies. Johnson, a Purdue University Extension weed control specialist, looked at pictures of specific fields and offered possible recommendations for best weed control.
Below are two cornfields in early spring. Both will be no-tilled into soybeans with a split-row planter when soil and temperature conditions allow. Johnson offers the following weed control suggestions:
The first field has green weeds growing before planting. Knowing this field will be no-tilled, the first task is deciding on the best burndown choice, Johnson says. He noticed winter annuals, Canada thistle and dandelions. Notes indicate the photo is representative of the entire field. Patches of thistles and dandelions were scattered throughout.
SIZE UP WEEDS: How many weeds can you see in this field already? Bill Johnson says you can adjust weed control plans based on weeds in the field.
Best choices for burndown would be 2,4-D or dicamba, Johnson says. However, dicamba has lengthy plant-back restrictions if soybeans aren’t dicamba-tolerant Xtend beans. There are plant-back restrictions with 2,4-D even if they are Xtend varieties.
“I would lean toward dicamba if you could plant Xtend varieties, because it’s better on thistles and just as good on dandelions,” Johnson says. If you plant Xtend beans, then XtendiMax, Engenia or FeXapan would be potential burndowns, and you could legally follow and plant without a plant-back restriction.
“I would probably spray and wait a day to plant to give weeds a chance to move herbicide throughout the plant,” Johnson says.
If you’re following with glyphosate-tolerant beans, then you’re likely back to 2,4-D and plant-back restrictions. Remember to cover your bases with other residual herbicides for broadleaf and grass control, depending on what other weeds you expect to emerge later.
The second field looks clean now, but Johnson leans toward applying residual herbicides preemergence. Waiting and scouting weeds that come through and then making a postemergence application is an option, but it can be risky depending on which weeds you typically battle.
STILL NEED HERBICIDES: Fall herbicides resulted in a clean field in the spring. However, Bill Johnson says you still should spray residual herbicides, keeping your toughest weeds in mind.
As it turns out, marestail is a tough competitor here most years, but no marestail has emerged yet. One option for a residual is to use Sharpen, Sencor, Valor, Authority or Zidua. If there are grasses present, add glyphosate. If you’re planting Xtend varieties, you could apply dicamba after soybeans emerge, Johnson says.
If you’re in non-GMO or glyphosate-resistant beans, Johnson recommends Sharpen, Sencor, Valor, Authority or Zidua. If grasses have emerged, add glyphosate or paraquat.
The bottom line is not to skimp on weed control just because the field is clean now, Johnson says. Instead, take advantage of the clean field as a great starting point and prevent new weeds from emerging.
Editor’s note: This is another story in a series of weed control articles using real-life fields as examples for how to build effective weed control programs. Recommendations are not all-inclusive.