The U.S. Environmental Protection Agency executed search warrants in parts of southeastern Missouri earlier this month to look for signs of improper use of the herbicide dicamba, the agency said on Tuesday.
The searches stemmed from complaints that dicamba, which has only been approved for application on fields before planting season or after harvest, damaged 41,000 acres (16,600 hectares) of soybeans and other crops. The complaints allege that improperly applied dicamba drifted into neighboring fields.
Dicamba can injure crops that are not resistant to dicamba, reducing final yields.
The warrants were executed the week of Oct. 10 at sites in Cape Girardeau, Dunklin, New Madrid and Stoddard counties as part of a criminal investigation, the EPA said. The agency did not specify what sites it searched.
Monsanto this year began selling a new dicamba-resistant soybean seed, Roundup Ready 2 Xtend, in the United States. Farmers have said that has led to an increase in the unapproved use of dicamba as growers planting those seeds can spray the herbicide without worrying about damage to their crops.
The EPA is expected to make a decision this autumn about whether to approve dicamba application on soybean fields that have already been planted, known as "over-the-top" application.