Palmer Pigweed – How To Battle The Scourge Of The South

Battling glyphosate-resistant Palmer Amaranth (aka Palmer pigweed) has become a major focus of crop producers across the South, especially in cotton and soybeans.

Alan York, Professor Emeritus at North Carolina State University, is one of the leading researchers exploring ways to control glyphosate resistant Palmer Amaranth more effectively, and he says it’s a challenging job.

We asked him about the weed and what makes it so tough to control.

“It has a number of characteristics about it,” he explains. “Over all you can say it’s a very vigorous growing plant– a very tough, competitive plant. “There’s physiology inside the plant that helps it deal with drought conditions. Bottom line, it can be bone dry and the crop wilting and Palmer amaranth is happy. It grows fast.

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“When it initially starts it’s not that fast but once it gets to 4 to 6 inches, it’ll easily grow one inch a day and under good conditions it’ll grow two inches a day. Also, it produces a lot of seeds. We’ve actually documented plants in North Carolina last year with 1.5 million seeds per plant.”

So what recommendations does York have for controlling Palmer amaranth successfully? Here are some pointers:

COTTON

  • Apply at least one residual herbicide either prior to or right behind the planter.
  • Use more than one active ingredient to get better weed control pre-emergence.
  • In conventional tillage cotton, York recommends starting with a soil-incorporated herbicide.
  • For the conservation tillage grower he strongly recommends a residual herbicide in the early burndown 3 or 4 weeks ahead of planting followed by a pre-emergent herbicide.
  • Add a residual herbicide to post-emergence sprays.
  • Consider a layby directed spray. “I think there’s a lot of value to a layby directed spray,” he says. “I know they’re a pain to put out but they really work and I really recommend them.”

SOYBEANS:

  • York is seeing a trend in full-season (i.e., not double-cropped) soybeans where growers are applying a residual herbicide ahead of planting.
  • Again, using more than one active ingredient will give more complete control of weeds and help control resistant weeds more effectively.

University of Georgia Extension Weed Scientist Stanley Culpepper offers some timely tips and recommendations on Palmer amaranth control as well.

The challenge is dealing with all of the curveballs that you get, like getting 8 inches of rain.

“It’s unfortunate that (commodity) prices are low, but you still have to control the Palmer amaranth,” Culpepper emphasizes. “You can’t cut corners with this weed. We have to be and remain aggressive. It’s not a one-season battle. If you cut corners one year, all of the hard work we’ve done the last five years is down the drain.”

The most important recommendation from Culpepper is timeliness:

“The timeliness of the sprays is critical,” he says. “The challenge is dealing with all of the curveballs that you get, like getting 8 inches of rain. Growers know what to do but getting the weed control out there in a timely fashion can be hard. But it’s critical.”