Monsanto Co's (MON) 4,550-word instruction label for its latest flagship weed killer, dicamba, has left some U.S. farmers and weed scientists confused over how to safely use the chemical product and driven Monsanto into an EPA review of the product, Reuters reported.

The weed killer, which is sold under different brand names by BASF (BASFY) and DuPont (DD) , can vaporize under certain conditions, allowing it to blow with the wind and damage or kill crops that have not been genetically engineered to resist it.

Dicamba has already been banned in Arkansas and is currently under review by U.S. regulators. The product was recently cited in a lawsuit in federal court as evidence Monsanto's product could be virtually impossible to use properly given its complex, lengthy instruction label.

The instructions require farmers to follow strict guidelines for wind speed, temperature and spray equipment use. Monsanto is banking on dicamba's success and its pending EPA review, as the company recently increased its outlook for U.S. plantings to 20 million from 15 million on higher sales of the Xtend soybeans on which dicamba is used.

Monsanto stock traded down 0.2% at Friday's close to $116.87. Shares are up 11% year-to-date.

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