Waterhemp and Palmer amaranth are both members of the pigweed family that significantly threaten crop yields and farm incomes across the U.S. Weed scientists with The Ohio State University have worked with the United Soybean Board and the Ohio Soybean Council to launch a local campaign, “No Pigweed Left Behind,” to ensure growers have tools to fight these invasive weeds.

“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.”

Pigweeds are so problematic because 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 an issue 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.

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 sheetcan 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 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 including 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.

Pigweed Resources
Use these resources to learn more about pigweed and how to control it:

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