Herbicide Diversity Needed

Using a diverse herbicide application strategy may increase costs, but a five-year Purdue University study shows the practice will drastically reduce weeds such as marestail, also known as horseweed, and seeds that are resistant to the popular herbicide, Roundup. It is Roundup?EUR??,,????'?????<

 

Excess usage of glyphosate-resistant crops has led to weeds, such as marestail, that also are resistant to glyphosate, the herbicide used in Roundup. Bill Johnson, a Purdue associate professor of weed science, said changing management practices can almost eliminate resistant marestail and its viable seeds in the soil. ''Another herbicide application is expensive, and it means more trips,'' Johnson said. ''But we can reduce the population and density of resistant weeds.''

Marestail, also known as horseweed, was the first weed to develop resistance to glyphosate. Other weeds also are adapting, Johnson said, reducing the effectiveness of products such as Roundup, the most widely used herbicide on the market.

It is Roundup's popularity that is contributing to its diminished effect. Johnson said farmers have come to rely on Roundup Ready crops that resist glyphosate as an easy way to control weeds. But overuse of any herbicide allows weeds to adapt and develop resistance. Johnson's study found that using a variety of herbicides in addition to Roundup before planting and alternating between Roundup and other herbicides can significantly reduce marestail. Sites that had three resistant weeds for every susceptible weed while using only Roundup and Roundup Ready crops saw weed populations drop to one resistant weed for every six susceptible weeds while rotating herbicides as Johnson suggests. That rotation also may lead to a 95 percent decrease in the number of viable marestail seeds in the soil. The results of Johnson's five-year study were published in the Journal Weed Science.