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PalmerAmarath1540x800 Photo courtesy of Howard F. Schwartz, Colorado State University, Bugwood.org.
Palmer amaranth with seed head, growing in a Colorado crop field.

7 tips to battle pigweed

Weed is especially challenging to control because a single female plant will produce hundreds of thousands of seeds.

A new community-based awareness initiative is informing growers about the risks of waterhemp and Palmer amaranth and teaching them how to fight back.

Weed scientists with The Ohio State University have worked with the United Soybean Board and the Ohio Soybean Council to launch a “No Pigweed Left Behind” campaign in their state, where problematic pigweeds (Amaranthus species) have been spotted in multiple counties.

“Our goal is to hold the line against pigweed and avoid large-scale infestations,” says Mark Loux, Ph.D., of The Ohio State University. “We want growers to understand they can’t beat these weeds with herbicides alone.”

What makes pigweed (especially Palmer amaranth and waterhemp) so problematic?

A single female plant will often produce hundreds of thousands of small seeds. The weed grows rapidly – as much as three inches a day under ideal conditions. That’s a problem since most post-emergence herbicides must be applied when the plants are less than three inches tall. To add to the complexity, pigweed plants can rapidly develop resistance to multiple herbicides.

What is the “No Pigweed Left Behind” campaign designed to do?

The campaign is designed to raise grower awareness and to provide specific tips and techniques for controlling the weed before it goes to seed.

How are growers being informed of the campaign?

Bumper stickers, brochures and other new campaign materials are being handed out at meetings, workshops and conferences and to agricultural dealer groups, extension agents and others likely to be working one-on-one with growers.

“If an agronomist arrives at a local farm with one of our ‘No Pigweed Left Behind’ magnets on their truck, it’s a great conversation starter and gives them a chance to share what they know about pigweed and how it is best controlled,” Loux said.

How can you battle pigweed?

  1. While the campaign is focused in Ohio now, the team at The Ohio State University recommends the following best practices that can be implemented wherever you farm:
  2. Know what pigweed looks like. There are a number of pigweed species with varying leaf shapes and characteristics, so it’s important to study up. This handy fact sheet can help you identify members of the pigweed family, including Palmer amaranth, waterhemp, spiny amaranth, smooth pigweed and redroot pigweed. 
  3. Be careful of cross-contamination. If you purchase or lease equipment, know where it has been. Avoid combines, plows and custom harvesting equipment used in areas known to harbor pigweed. Avoid cotton feed products or hay that might contain pigweed, as well as manure from animals fed with cotton feed products.
  4. Scout for pigweed. Inspect fields continually throughout the growing season for pigweeds that might have escaped herbicide applications. Pay special attention to recently seeded cover crops, Conservation Reserve Enhancement Program plots, field buffers, roadsides and natural areas where problem pigweeds might be lurking.
  5. Be smart about herbicide selection. Use residual herbicides to control early-emerging pigweed, but mix things up instead of relying on a single herbicidal site of action. Herbicide applications that include multiple sites of action still effective on the targeted pigweed population can slow the development of resistance.
  6. Avoid seed dispersal during harvest. If you spot patches of pigweed as crops are being harvested, make certain to avoid them. Running a combine over pigweed can disperse seeds and prove problematic for years to come.
  7. Use safe removal techniques. If you spot pigweed plants that have yet to produce mature seeds, pull them or cut them off just below the soil line. Plants with mature seeds should be bagged before being removed and destroyed. Either burn the plants or bury them under at least a foot of compost.

Want more information?

Consult the following resources to learn more about pigweed and how it is best controlled:

Source: The Weed Science Society of America, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset. 
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