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On a research plot near the Rochester airport, Jared Goplen has watched weeds for the past three summers. His specialty is giant ragweed, one of more than a dozen species of “superweeds” that resist the most widely used ­herbicides. Superweeds can take over cropland, reduce yields and wipe out farmers’ profits. Even consumers can face a secondary effect in the form of higher food prices.

“It’s a serious problem and one that will continue to grow,” said Paul Meints, research program manager for Minnesota Soybean.

Weeds that won’t succumb to mainstream herbicides are a rising concern nationally, especially in cotton, corn and soybean country, and the largest agribusinesses are racing to propose solutions. In Minnesota alone, growers plant nearly 16 million acres of corn and soybeans each year.

Goplen, a University of Minnesota graduate student, is testing whether crop rotation and other non-herbicide methods can make a difference in keeping weeds under control. He records the number of giant ragweeds as they come up, collects and counts seeds that fall from mature plants, and even sifts seeds in the soil to map hot spots in the seedbank where seeds are waiting to sprout next year. 

In states such as Arkansas, Tennessee and Georgia, the primary menace is a different weed.

Thousands of acres of soybeans and cotton had to be mowed down in recent years because the herbicide-resistant Palmer amaranth had overrun the fields.

Meints said the Palmer weed has reached southern Iowa but is not yet in Minnesota, where farmers grow more than 7 million acres of soybeans and about 8.5 million acres of corn. No Minnesota farmers have lost entire crops to herbicide-resistant weeds, he said, but some have experienced yield losses.

University researchers and grower associations have pushed hard the past couple of years to let farmers know that using the same herbicide year after year is a bad idea, Meints said, and that herbicides and crops need to be rotated more frequently to lessen the chances of runaway superweeds on their fields.