That layby application you made, or didn’t make, matters when it comes to continued pigweed control in cotton, and it can help preserve a valuable tool.

“A lot of our growers are challenged with their time, and unfortunately a lot of them have decided to not use a layby application, or hooded application. Our research is saying that's a really bad idea when it comes to fighting Palmer amaranth. That layby application allows us to do several things,” said Stanley Culpepper, University of Georgia Extension weed specialist.

Culpepper was one of the presenters of the 30 stops at the annual Sunbelt Ag Expo Field Day held in Moultrie, Ga., July 25.

With a layby application, Georgia cotton growers get a valuable chance to deploy substitute urea chemistries, such as diuron, which are not used in any other agronomic crops. “And these chemistries are very effective, not only in controlling the emerging pigweed, but they also give excellent residual control to let the cotton close out. … When our growers pull these precision, timely applications out and they go over the top, a lot of times we don't get good enough coverage of those weeds high under the cotton.”

In a cotton test plot at the Sunbelt Ag Expo farm, Culpepper applied a pre-emergence, which is always needed, and then delivered sequential Roundup-Dicamba applications over the top, or a what would be considered a standard program. He then came in with a layby application of Roundup plus diuron along with a little bit of Envoke to clean up morning glory. “There's not one pigweed plant per acre left where we ran that system,” he said.

On an adjoining test plot, Culpepper followed the same standard herbicide system going over the top, but left out the layby application. In the test plot without the layby, he had what would equate to 1,400 Palmer amaranth plants per acre, which may not necessarily look like a lot when you ride by on the road. But think about it, he said.

“Half of those plants are females. Those females are going to produce upwards of a half a million seed per plant. If for some reason one survived those Roundup-Dicamba applications we made, we really ought to be concerned. If it's resistant or is tolerant to dicamba, just one of them, and produces that progeny, here we go. In three years, we could lose this chemistry,” he warned.

Last year, Culpepper surveyed about 400 cotton growers and of those about 40 percent were still using layby applications as part of their weed management program. Of course getting that percentage higher would be good, he said.

“I know we can't necessarily get (layby applications) on every acre, but 99 percent would be wonderful, right? But we all know where our problem fields are. We know the fields that have the most Palmer Amaranth. We know just from experience. That's where we want to start the focus,” he said. “The ability to use different chemistry that's very effective on emerged (pigweed) and residual control with that ability to get good coverage under the cotton. That full coverage is critical and essential for long-term sustainability.”