Monsanto reportedly prevented key independent testing of its XtendiMax herbicide when introducing the product to market.

Monsanto denied requests by university researchers to study the volatility of the XtendiMax with VaporGrip product, Reuters reports. Volatility measures the product's tendency to vaporize and drift across fields.

Researchers from the University of Arkansas, University of Missouri and the University of Illinois told Reuters that Monsanto provided samples of XtendiMax prior to the product's approval by the EPA but also sent contracts forbidding volatility testing.

"This is the first time I’m aware of any herbicide ever brought to market for which there were strict guidelines on what you could and could not do," Jason Norsworthy of the University of Arkansas told Reuters.

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Scott Partridge, Monsanto's vice president of global strategy, told Reuters that Monsanto prevented the testing because it was not necessary because the XtendiMax product was less volatile than a previous formula of dicamba that had been deemed to be safe.

Partridge said that collecting meaningful data takes a long time. "This product needed to get into the hands of growers," he told Reuters.

Monsanto is one of the top producers of dicamba, along with BASF SE and DuPont. Last month, Tennessee imposed new rules on the use of dicamba, becoming the fourth state to address complaints that the herbicide blows into other fields and damages crops.

Missouri also has issued restrictions for dicamba products. It had temporarily banned the products until it received "safeguards" from Monsanto and other companies. Arkansas has banned the herbicide for most usages, and Kansas also is investigating claims about dicamba.