(Reuters) – Missouri will limit the use of a weed killer made by BASF SE after farmers complained the chemical drifted and harmed their crops, following a move by Arkansas to prohibit sprayings next year of the herbicide and rival products.

Missouri on Thursday banned sprayings of BASF’s Engenia herbicide, which is based on a chemical known as dicamba, in 10 counties that had high numbers of complaints about crop damage, starting on June 1, 2018. The ban will expand statewide on July 15 and end in October.

Missouri said it expects to impose similar bans on dicamba herbicides sold by Monsanto Co and DowDuPont Inc.

The United States has faced a weed-killer crisis this year caused by new formulations of dicamba-based herbicides, which farmers and weed experts say harmed crops this summer because they evaporate and drift away from where they are applied.

Summer can be a riskier time for sprayings, experts said, because high temperatures can increase vaporization.

Manufacturers say the herbicides are safe when properly applied. The companies need to convince regulators, though, after farmers flooded state agriculture departments with complaints about crop damage associated with the products.

The herbicides will carry tighter usage instructions next year, and the Environmental Protection Agency could block sales if complaints persist.

Missouri wants the EPA to keep dicamba herbicides on the market to give farmers options for weed control, said Chris Chinn, director of the state’s department of agriculture.

“We wanted to make sure we had a very successful year in 2018,” she said.

BASF and DuPont, which makes the herbicide FeXapan, declined to discuss details of Missouri’s restrictions.

Nationwide, 3.6 million acres of soybeans suffered harm associated with dicamba, and states launched 2,708 investigations into dicamba-related crop damage, according to data compiled by the University of Missouri.

Missouri received about 310 complaints from growers related to dicamba, second only to the nearly 1,000 filed in Arkansas.

Arkansas blocked the use of Monsanto’s herbicide, XtendiMax, on crops this year. A state board voted this month to ban it for a second summer, along with the products sold by BASF and DuPont.

Monsanto, which is being acquired by Bayer AG for $63.5 billion, sued Arkansas to prevent the state from prohibiting sprayings after April 15, 2018.

The limits on Engenia use in Missouri are “more reasonable” than Arkansas’ proposed deadline for dicamba sprayings, said Scott Partridge, vice president of global strategy for Monsanto.

“There’s really no science that supports an arbitrary cutoff date,” he said.