Purdue University Extension weed control specialist Bill Johnson visited two fields to assess weed control after a burndown application. Corn is emerging in both fields, located counties apart in Indiana. Johnson actually didn’t physically visit these fields. He did so virtually through pictures. After all, these fields were observed in 2020, the “virtual year.”
Johnson believes there are lessons here about what works and what doesn’t work when it comes to burndowns, and how to control tough weeds that may appear in continuous no-till fields. Here’s a closer look.
The field above, featuring green corn spiking through mostly brown vegetation, still has a few weeds remaining. “The ones that stick out are nutsedge and dandelion because those are ones you would need to deal with as escapes,” Johnson says. There is also some chickweed and common mullen present, but they will likely be less of a problem.
“Looking at your field at this stage is a good practice because you can see what the burndown and residual worked on, and what escaped,” Johnson says. “If this is representative of the entire field, you would need to deal with the nutsedge and dandelions yet this season.”
Johnson’s guess is that the burndown was probably glyphosate. “It’s weak on winter annuals and dandelion, especially if you’re spraying in cool weather,” he says.
Adding 2,4-D or dicamba to the burndown probably would have taken care of the dandelions, he says. For nutsedge, Permit could have been added. To control the nutsedge escapes, he would recommend Permit. A dicamba product postemergence would control dandelions.
In the field below, corn was planted into grass. You can see corn plants beginning to emerge in the lower right corner of the picture.
“The real lesson here is figuring out why the burndown didn’t work better than it did,” Johnson says. “The grass isn’t dead, and there are still dandelions present.
“We don’t know what was applied. The burndown may not have been appropriate for what was present in the field.” For example, if it was glyphosate, it wouldn’t have taken out the dandelions, Johnson adds.
This picture was taken on June 1. May was cool throughout the eastern Corn Belt.
“One possibility is that it was just too cool for the burndown herbicide to be as effective as it should have been,” Johnson says. “The other possibility is that someone tried to shave rates, and you simply can’t do that when you’re trying to burn down this much vegetation.”
Or it could have been the trifecta, he adds. Perhaps it was a burndown herbicide not effective on established grass or perennials, applied at low rates when it was cool.
“The message here is that it doesn’t pay to cut corners,” Johnson says.