CHICAGO (Reuters) - Monsanto Co invited dozens of weed scientists to a summit this week to win backing for a controversial herbicide but many have declined, threatening the company’s efforts to convince regulators the product is safe to use.

Monsanto logo is displayed on a screen where the stock is traded on the floor of the New York Stock Exchange (NYSE) in New York City, U.S. on May 9, 2016. REUTERS/Brendan McDermid/File Photo

Monsanto faces a barrage of lawsuits over its dicamba herbicide and risks of tighter restrictions on its use, after the chemical drifted away from where it was sprayed this summer and damaged nearby crops unable to tolerate it.

Arkansas and Missouri suffered the most complaints of U.S. states with damage linked to dicamba. Weed scientists from the two states declined to attend the summit on concerns about Monsanto’s response to the incident.

The company plans to present data at the summit that it says show user error was behind the damage, contrary to academics’ findings that dicamba products can vaporize and move off target under certain conditions in a process known as volatilization.

Missing will be Kevin Bradley, a University of Missouri plant sciences professor who has tracked the number of crop acres nationwide that have been hurt by dicamba sprayings. Bradley said he believed Monsanto was not willing to discuss volatilization.

“I think it’s best for me to stay away from that,” he said.

To prevent damage next year, states and the U.S. Environmental Protection Agency (EPA) are considering new rules for usage, decisions to be based partly on advice from university weed scientists invited to the meeting, whether they attend or not.

Tighter restrictions could hurt sales of the herbicide or of Monsanto soybean seeds engineered to resist the chemical, the company’s biggest ever biotech seed launch.

Arkansas on Thursday moved just one step away from barring sprayings of dicamba next summer, setting the stage for a potential legal showdown with Monsanto.

Time is now of the essence as farmers start to make planting decisions for next spring.

The EPA has held calls with university weed experts to discuss potential regulations.

BASF SE, which also sells a dicamba-based weed killer, has invited scientists to its own meeting on the herbicide. The American Soybean Association, which represents farmers, is convening a meeting, too.

Monsanto’s summit, to be held near the company’s headquarters in St. Louis, will be the largest meeting so far on dicamba, said Scott Partridge, the company’s vice president of global strategy. At least half of about 60 invitees will attend and hear presentations from Monsanto and outside experts, he said.

Reuters contacted 10 scientists who were invited. Of these, three said they would attend and seven said they would not, for reasons including scheduling conflicts.

“We want them to challenge us and we intend to challenge those who are presenting data,” Partridge said.

INTEGRITY QUESTIONED

Monsanto recently upset U.S. weed scientists by questioning the objectivity of two Arkansas experts, Jason Norsworthy and Ford Baldwin, who said dicamba had problems with volatilization. The specialists could be biased against the chemical because they were affiliated with Bayer AG, which sells a competing system to control weeds in soybeans, according to Monsanto.

Norsworthy, a University of Arkansas professor, has declined an invitation to speak about volatilization at Monsanto’s meeting, according to the university. Last year, the EPA cited his research on the best way to use dicamba when the agency approved the use of the chemical on crops that can resist it.

Two other University of Arkansas experts, Tom Barber and Bob Scott, will also not attend.

“With Monsanto questioning of the integrity of our science, we felt it was best not to participate,” university spokeswoman Mary Hightower said.

Monsanto highlighted connections Norsworthy and Baldwin had to Bayer to ensure that Arkansas fairly reviewed dicamba, Partridge said.

In July, Arkansas banned dicamba use for 120 days.

MONSANTO MONOLOGUE?

Monsanto’s critiques of experts follows past accusations by farmers and activists that the company improperly influenced science.

In March, farmers and others suing Monsanto claimed in court filings that Monsanto employees ghostwrote scientific reports that U.S. regulators relied on to determine that glyphosate, a chemical in its Roundup weed killer, did not cause cancer.

In 2015, the New York Times reported U.S. academics who received grants from Monsanto were used in lobbying and corporate public relations campaigns to defend the safety of genetically engineered food.

Monsanto will cover travel costs for academics who attend this week’s meeting, as is customary for the company, spokeswoman Charla Lord said.

Among those attending will be University of Tennessee weed scientist Tom Mueller, who told Reuters he planned to pay his own way and was skeptical Monsanto would engage in discussions.

“I think it’s just going to be a monologue,” he said.

Mueller said U.S. weed scientists had discussed skipping the meeting because they were upset Monsanto had criticized the Arkansas scientists.

“There’s some pretty strong sentiment that some states won’t send anybody,” he said. Reuters did not confirm that any states would have no representatives at the meeting.