What is in this article?:
• The three keys to managing pigweed are: Start clean, overlap residual herbicides, and manage escapes.
• To manage pigweed the seed bank must be stable or decreasing every planting season to achieve sustainability.
Must reduce seed numbers
To manage pigweed, Smith says, the seed bank must be stable or decreasing every planting season to achieve sustainability. He showed the 200 or so cotton farmers in the audience a picture of a female pigweed plant he calls Elvira. “In the lab, we counted 1.8 million seed from this one plant, which looked more like a tree and could shut down any cotton picker foolish enough to take it on,” he says.
Controlling pigweed is a numbers game that farmers simply cannot win, the Arkansas weed scientist adds. Elvira is a bit atypical of female pigweed plants, but the more typical plants consistently produce 200,000-300,000 seed if left untreated.
If 95 percent of the seed die during the winter months and the farmer gets 99 percent control from his herbicide program, he still has more than 3,000 pigweed plants. If half are female, the farmer has the potential of having another half million or so pigweed to deal with the next year. “It’s truly a numbers game that farmers won’t win,” Smith says.
If there is a good side of pigweed management it is that these weed seeds don’t last long in the soil. Usually four years is about the life span of Palmer amaranth pigweed in the soil. By comparison, cocklebur survives in the soil 25 years or more.
This short life cycle gives growers some options for keeping the seed bank under control. Keeping a field clean over a relatively short period of time gives growers a chance to get ahead of the numbers game and at least have a chance to control these yield-robbing weeds.
During the NPE program, farmers Bowen Flowers from Clarksdale, Miss.. and Kent Wannamaker from St. Matthews, S.C., shared some of their experiences in dealing with pigweed.
The ante goes up considerably on pigweed when you get weeds that are tolerant to glyphosate, Flowers says. “It’s one of those deals where you can pay me now or you can pay me a lot more later. Unfortunately, our farming operation fit into the pay me a lot more later category,” the Mississippi grower adds.
“In 2009, we cleaned up some land that had some resistant pigweed on it. We thought we did a good job and it didn’t look like much of a problem. In 2010, I sprayed my burn-down treatment and planted without any residual herbicide.
“We got a good rain, and up came the pigweed. We sprayed with glyphosate and killed at least 80 percent of the new flush of weeds. Once the 20 percent left over got over six inches tall, we had a big mess on our hands.
“We had 100 acres of cotton that we ended up disking up because we just couldn’t control pigweed. On the rest of our land, it cost a lot of money — a lot of ‘pay me later’ — to grow cotton on much of land,” Flowers says.
In 2011, the Mississippi grower says he took the ‘pay me now’ approach. “In February, we burned down with glyphosate and 2,4-D. Three weeks before planting we applied Reflex and at planting we applied Gramoxone and Cotoran behind the planter.