Diversity key to successful herbicide use

Using a diverse herbicide application strategy may increase production costs, but a five-year Purdue University study shows the practice drastically reduces weeds and seeds that are resistant to a popular herbicide.

Overuse of glyphosate-resistant crops has produced weeds such as marestail that aren't killed by the herbicide in Roundup, said Purdue Extension weed specialist Bill Johnson. Changing management practices can almost eliminate resistant marestail and its viable seeds in the soil.

Marestail, also known as horseweed, was the first weed to become glyphosate-resistant, according to Johnson's study. Other weeds also are adapting, he said.

Using a variety of herbicides in addition to Roundup before planting and alternating between Roundup and other herbicides in corn can significantly reduce marestail, Johnson said.

Continuing with only Roundup and Roundup Ready crops can intensify the problem, Johnson said.

The Indiana Soybean Alliance, BASF, Dow AgroSciences, Monsanto and Syngenta funded Johnson's study, which will continue looking at management strategies to reduce the numbers of other weeds that have built up a resistance to glyphosate.