Palmer Amaranth Hates A Thick Biomass Blanket

"Every year or two years we can keep the (Palmer) seed from germinating, that seed is rapidly dying."

Published on: Mar 20, 2012

Herbicide-resistant Palmer amaranth, or pigweed, has changed the cotton game in the Southeast, unfortunately forcing many growers to abandon traditional conservation tillage practices in an effort to control the fast-growing, prolific weed. But the monster has weaknesses, ones that can be exploited to keep conservation in cotton's future.

For all its strength, Palmer's seeds are relatively weak. They don't last long in the ground and need plenty of sunlight to germinate. Cover crops, particularly ryegrass, can create enough mass to blanket a field, block sunlight and prevent the seeds from emerging, stopping them long before they become a problem for a grower, said Stanley Culpepper, a weed specialist with the University of Georgia's Cooperative Extension.

Palmer Amaranth Hates A Thick Biomass Blanket
Palmer Amaranth Hates A Thick Biomass Blanket

"Any cover crop can do, but I've been more successful with rye. But if I can get a significant amount and I can roll that rye just before I go in and plant, I basically create a barrier where the sun can't get to the soil," Culpepper said. "And when the sun can't get to the soil, Palmer amaranth will generally not emerge or germinate."

Snuffing out the seed bank is a must in any Palmer control. With a high-biomass approach like a heavy rye cover crop reaching seven to eight feet tall rolled to the ground, as much as 80% of a field's Palmer seed bank can be eliminated in just a few years. "Every year or two years we can keep the (Palmer) seed from germinating, that seed is rapidly dying," he said.

But the system isn't perfect, yet, he said, but it is looking very economical compared to the measures, and money, now being used to combat the weed. The greatest limitation to the system is what Culpepper calls "blowout," or when the rye wraps around the ripper shank and causes the soil to blowout, leaving an uneven bed or furrow for the seed and potential for a non-uniform stand.

"If we can't address (blowout) the average cotton producer will not move to this system," he said. "But I'm really optimistic that we've got some neat ideas that over the next year or two not only we'll we produce a sound system, we'll solve or greatly reduce the potential for blowout for these growers."

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