Waterhemp and Palmer amaranth, both members of the pigweed family, have become significant threats to crop yields and farm incomes across the Americas. In the U.S., they compete with crops in the South and in parts of the Midwest, but according to the Weed Science Society of America (WSSA), a new community-based awareness initiative is informing growers about the risks 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.
The “No Pigweed Left Behind” campaign is designed to raise grower awareness and to provide specific tips and techniques for controlling the weed before it goes to seed. For years Loux and his colleagues have shared information on pigweed with crop advisors, but they wanted to raise visibility and broaden their reach. Now catchy and colorful “No Pigweed Left Behind” materials are being used to call attention to their cause.
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.
Pigweed Best Practices
So how do you battle pigweed if herbicides alone aren’t enough? The team at The Ohio State University recommends the following best practices:
1. 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.
2. 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.
3. 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 (CREP) plots, field buffers, roadsides and natural areas where problem pigweeds might be lurking.
4. 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.
5. 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.
6. 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.