Southern Minnesota has some of the most productive farmland in the world, producing corn and soybeans at an impressive rate and providing a major economic boost to the region and the state.

For years many have warned of the threat of “superweeds” moving into the row crop fields of the Midwest. But many in the ag community and the chemical companies that make weed killers have ignored or pooh-poohed the threat. Now the first of the superweeds has made its appearance in southern Minnesota — and it’s a nasty one.

Palmer amaranth is a highly aggressive weed that can grow 8 feet tall and has a thick woody stem that as one scientist said is “almost chain saw material.” It is already causing major economic damage in the cotton fields of the south and it has been slowly moving north. The weed has shown up just northwest of the Mankato region in Yellow Medicine County. The weed seed was among a prairie seed mix that more than a dozen farmers planted. Ag officials are burning and attacking the weed in hopes of slowing its movement into row crop fields, but the vigorous weed can’t be eradicated.

The last line of defense for farmers — weed killers — also won’t work on the weed. That’s because it, like other superweeds, has grown resistant to glyphosate, which is the ingredient in the widely used Roundup herbicide.

It is the unbridled use of Roundup that created the superweeds in the first place. More than a decade ago, corn, soybean and cotton plants were genetically modified so they would not be harmed by Roundup. The discovery was a boon. All farm fields could be sprayed without a weed showing up and without the crops harmed.

The argument in favor of the modified plants was that less herbicide would have to be used to control weeds. That was true for a time. Studies done by Washington State and others show that herbicide use declined in the first years, but has steadily increased since. That’s because weeds — and bugs — have a natural inclination to survive and to resist new threats like Roundup. That growing resistance by weeds and pests means farmers have to use more and more spray.

But with the weeds like Palmer amaranth, virtually no amount of spray — at least any safe amount — does anything. Scientists have tried spraying very high rates of glyphosate on the weed but it stays healthy while the crops suffer.

In 2014 the Texas Department of Agriculture, trying desperately to stop the spread of the weed there, asked the EPA for permission to use the restricted chemical herbicide propazine on millions of acres of cotton. The request had to be denied because of the high risk propazine would poison the water supply.

The advent of superweeds in America’s Corn Belt raises frightening and difficult questions. Its economic and environmental damage could be immense.

There are no easy answers. Development of a new wonder chemical is doubtful and even if something is created, we know from our Roundup experience that it will be a short-lived victory. Whatever the answers, it’s a serious debate that state and federal ag officials, the Legislature, universities, farm groups and others need to begin quickly.

— Mankato Free Press, Dec. 29