What is in this article?:
- Glyphosate-resistant pigweed in a class all alone among cotton pests
- Must stay ahead of the weed
• Growing at rates as fast as 2 inches a day, the weed has been known to reach a height of 9 feet and a weight of 40 pounds, far exceeding the dimensions of any of its competitors.
• From 2005 until now, this resistant weed has continued to spread throughout the Eastern Seaboard and down into south Alabama.
AUBURN UNIVERSITY EXTENSION weed scientist Mike Patterson explains the continuing battle against glyphosate-resistant pigweed during the recent East-Central Alabama Row Crops Workshop held in Shorter.
Anyone who is a college football fan is familiar with the five-star rating system for high school recruits — the biggest, fastest and meanest receive the top rating of five stars.
If such a system was applied to cotton weed pests, glyphosate-resistant Palmer amaranth pigweed undoubtedly would be in a class all alone, at six stars, says Mike Patterson, Auburn University Cooperative Extension System weed scientist.
Growing at rates as fast as 2 inches a day, the weed has been known to reach a height of 9 feet and a weight of 40 pounds, far exceeding the dimensions of any of its competitors, he says.
Speaking at the recent East-Central Alabama Row Crops Workshop in Shorter, Patterson recalled the history of Palmer amaranth, and when glyphosate was first sprayed on the weed species.
“In past years, we would spray glyphosate at the standard rate on Palmer amaranth that was knee-high and burn it down to the ground,” he says.
“In 2004-2005, there was one cotton field in south-central Georgia where a farmer noted he couldn’t kill Palmer amaranth with glyphosate. From 2005 until now, this resistant weed has continued to spread throughout the Eastern Seaboard and down into south Alabama.
“In 2009, it was discovered in a soybean field in north Madison County in Alabama’s Tennessee Valley. To the best of my knowledge, there are probably 26 counties in Alabama that have at least one field of glyphosate-resistant Palmer-amaranth pigweed. Farmers in central Alabama also have reported resistant pigweed,” says Patterson.
Some refer to resistant Palmer amaranth as “Frankenweed,” the monster weed, he says.
“One of the reasons it’s so hard to manage is that the seed production is very high. More than 1.7 million seeds have been documented on one plant. Even if you get 99.9 percent control of female plants, and you leave one or two per acre, with each plant producing at least a half-million seeds, you still have a lot of plants out there,” he says.
USDA researchers have been looking at resistant pigweed seed mortality, says Patterson.
(For another look at the numbers game, click here).
“Their research has shown that in the first year after those seed hit the ground, during the winter before the next season, as much as 50 percent of the seed will rot and won’t come up. But when you’re dealing with populations of hundreds of millions, you’ve still got a bad problem.”
Most weed scientists in the Southeast agree that farmers need to maintain residual control of this weed, from burndown all the way through layby, he says.
“If it’s as tall as your cotton in a Roundup Ready system, it’s extremely difficult to control, and it’ll put you out of business. With most residual herbicides in cotton, you get two to three weeks of activity.”
Soil residual herbicides once again have become a standby of cotton production, and one of the critical factors in controlling this weed, says Patterson.