WASHINGTON (Reuters) – The U.S. Environmental Protection Agency is reviewing its directions on how to use the latest versions of the weed killer dicamba, following hundreds of reports about crop damage when traces of it drift away from application sites, an agency spokeswoman said on Tuesday.

“We are reviewing the current use restrictions on the labels for these dicamba formulations in light of the incidents that have been reported this year,” EPA spokeswoman Amy Graham said in an email to Reuters.

The EPA approved new formulations of the pesticide, a weed killer sold by Monsanto Co, BASF and DuPont late last year. The authorization was only for two years because older versions were known to drift away from their intended targets and settle onto nearby fields.

Regulators in 16 states are investigating dicamba damage reports covering more than 2.5 million acres of crops, according to a report by University of Missouri Associate Professor Kevin Bradley published on July 25.