We’re already hearing that Palmer amaranth is making its presence known this season —both the University of Kentucky and Iowa State University reported infestations of the “pigweed on steroids” in their respective states recently, and it’s likely that more findings will pop up as the growing season continues.

When it comes to protecting your crops from Palmer amaranth, the old adage, “Prevention is the best medicine,” is your best defense. But we know that even the most aggressive prevention efforts may not keep a plant — which is capable of releasing 400,000 seeds and growing 2 to 3 inches per day — from making a home on your land. 

Here are 7 guidelines from Aaron Hager, weed science specialist at University of Illinois, on managing Palmer amaranth.

1. Verify its identity

Palmer amaranth can be confused with common waterhemp and redroot pigweed. If you suspect you have Palmer amaranth, send a leaf tissue sample to the University of Illinois for identification. This video by Purdue University can also help you identify Palmer amaranth in your field.

2. Physically remove the weed prior to flowering

Whether it’s confirmed or not, any plants you suspect of being Palmer amaranth should be physically removed by hoeing or hand-pulling. Hager notes that herbicides cannot be relied on for sole control. If you remove the plants by hoeing them, make sure to sever the plant stem at or below the soil surface to reduce potential for regrowth. Plants left on the field will re-root from stem fragments.

3. Leave the seed.

If Palmer amaranth isn’t identified until after brown to black-colored seeds are present on female plants, leave the weed undisturbed to avoid spreading seed.

4. Flag the area

Be sure to mark the area where Palmer amaranth seeds were produced. Intensively scout and implement an aggressive management plan the following season to prevent further seed production. 

5. Do not harvest it

Instead, physically remove the plants prior to harvest and either leave the plants in the field, or remove them by placing them in a sturdy garden bag. Bury or burn the bags in a burn barrel as soon as possible, Hager says.

6. Keep no-tilling

By continuing to utilize no-till practices you leave the seeds on top of the soil surface, thereby increasing opportunities for seed predation.

7. Use an integrated herbicide program

This should include soil-residual herbicides applied at full-recommended use rates of within two weeks of planting. Follow with post-emergence herbicides before Palmer amaranth plants exceed 3 inches in height. Herbicides that control waterhemp will also control Palmer amaranth.

Laura Allen,
Associate Editor
No-Till Farmer