Waterhemp is outsmarting herbicides all around Wisconsin. Here's how to get rid of this tricky native weed.

Samantha Hendrickson
Wisconsin State Farmer
Scientists are getting closer to finding the genes for maleness in waterhemp and Palmer amaranth, two of the most troublesome agricultural weeds in the U.S.

Waterhemp is one tough weed. And over the last five years, it's not just stayed tough —it's getting smarter.

This species of pigweed is outsmarting government-approved herbicides and killing corn and soybean crops statewide. It's spread across Wisconsin via wind, animals, waterfowl migration, contaminated farm equipment and normal combine use in invaded fields, with each plant spreading upwards of 30,000 seeds. 

What's unique about waterhemp, according to Rodrigo Werle, a University of Wisconsin-Extension professor and weed specialist, is that each plant has mutated to carry the "mother seed."

"It's everywhere around the state... and over the past few years, waterhemp has become a major problem," Werle said. "But it's not a new weed species. It's been here forever. It's become problematic because it has evolved resistance to the main herbicides we use to grow our crops." 

The weeds start germinating in May, and bloom in June, July and sometimes into August. It's large emergence window makes it difficult to contain.

If waterhemp growth is left unchecked, Werle said, farmers could be looking at 70-80% crop failure come harvest season. 

However, there is hope for getting rid of this weed, but it takes some significant strategizing in advance. There are several methods for getting rid of waterhemp, if you're willing to put in the work and a little money to save your crops in the long run. 

Waterhemp in soybean field

How to get rid of this well-adapted weed 

One method, Werle said, is making sure the plants never get to seed. Near the end of the growing season, farmers should make sure to get rid of the plants in their fields if their infestation isn't too bad.

"For waterhemp control, post emergence with chemicals is very challenging because the options are very limited, we have a lot of resistance out there. So the secret for waterontrol is to not let it establish," Werle said. 

Burning the seeds is one of the best ways to get rid of them. It's important to get rid of the seeds before harvesting, so that the combine doesn't spread the waterhemp seeds all over again. 

A second strategy to employ is planting cover crops. These compete with the waterhemp for the soil and manage its spread. It's also good for getting rid of other kinds of tricky pigweed. While this may cost a bit more money than just using herbicides, ultimately, Werle said, it's going to save you crops and money in the future. 

It may take three to four years to see differences with cover crops, but cover crops are the better solution for heavier infestations if you can't simply get rid of the weed after growing season. 

Crop rotation is also important, Werle said. If farmers rotate large grain and small grain crops, such as alfalfa along with their soybeans and corn, that can help manage waterhemp growth. 

Non-herbicide strategies are especially important this year, Werle said, as there will likely be a shortage in pesticides and herbicides next year due to supply chain shortages around the world. 

You can find more resources and studies on waterhemp and other pigweeds at UW-Extensions' weed website here. 

Samantha Hendrickson can be reached at 414-223-5383 or shendrickson@jrn.com. Follow her on Twitter at @samanthajhendr.