Alan York has a clear message for North Carolina cotton farmers this year: “Don’t let up on Palmer.”
Speaking at an Extension cotton meeting in Rocky Mount Feb. 1, York, Williams Neal Reynolds professor of crop science at North Carolina State University, said progress has been made in Palmer Amaranth control in the best five to 10 years, but pigweed continues to be the number one weed worry in North Carolina.
“I encourage you don’t let up on it,” York told the cotton farmers. “I know coming in after a bad year, you’re looking for ways to cut costs anywhere you can but don’t slack up to much on this one. We think the way to get ahead and stay ahead of Palmer Amaranth is to work on the seed bank.”
York pointed to data from Georgia that shows that the viability of palmer Amaranth seeds is basically gone if it has been dormant for about three years. “Eighty to 90 percent of those pigweed seeds ae not viable after three years. If you can go two to three years without making a crop of seed, you’re going to get a head start on this weed,” York said.
York said N.C. State’s recommendations for palmer Amaranth control basically are unchanged.
“If you’re in no-till or strip-till, we still like to see something residual as a burn down. That’s where we tended to use a flumioxazin product. We still want a 2, 4-D or a dicamba in burn down,” York said.
“But if you are in conventional tillage, you’re going to be working the land anyway, so don’t forget things like Treflan and Prowl incorporated for pigweed control. We like some residual behind the planter, and I like at least two active ingredients. That can be a Warrant-Reflex, a Warrant-Direx or a Reflex-Direx. We like at least two modes of action. I’ve been very pleased with a three-way mix of Warrant, Reflex and Direx.”
York also encourages reduce rates of those compounds. He suggests two pints of Warrant, 10 to 12 ounces of Reflex and one pint of Direx. “We tend to be cutting some of the injury back, but we’re getting very good control,” he said.
York stressed the importance of timely post-emergence herbicide applications.
“Most of you are using Liberty to take care of the palmer. You know that if it’s bigger than about two and a half inches, then you have better had paid the preacher if you’re going to kill it. We have to be timely. We need some residuals. We need some Warrant, some Dual or some Outlook,” York said.
“We are using a lot of Liberty dealing with this Palmer Amaranth. We need to be careful that we don’t abuse it and select for resistance. If you’re in a program using Liberty, make sure you continue to use your residuals when you plant. Limit that Liberty to two shots per year. Use timely applications. We know when you start cutting rates, that encourages resistance,” York said.
“When we start treating weeds way too big, then that’s asking for difficulties with resistance. Put the full rate of Liberty. We need to get good coverage. We need some residuals in with the Liberty post. Good coverage includes residuals,” he advised.
In addition, York said a residual layby application of herbicide is critical in effective Palmer Amaranth control. “A layby still has a place in resistance management,” he said.