The chemical weed killer dicamba is so controversial that it has spawned a federal class-action lawsuit against its manufacturers, California restricts its use on farms and Arkansas has temporarily banned its use on farms.

But good luck finding out if the herbicide is even being used on farms in Hawaii, where the state doesn’t regulate dicamba.

“It’s not a restricted use pesticide,” said Janelle Saneishi, a spokeswoman for the Hawaii Department of Agriculture. “You can get it over the counter.”

Dicamba made big news on the mainland over the summer because of problems arising from a new use for the weed killer. Farmers have used dicamba for more than 50 years to clear fields in the spring before planting, said Jason Norsworthy, an agricultural weed scientist at the University of Arkansas in Fayetteville.

But things changed in recent years as big biotech companies developed genetically modified, dicamba-resistant varieties of crops like soybeans and cotton. Those crops are designed to help farmers deal with weeds that have evolved to tolerate glyphosate, the active ingredient in herbicides like Roundup, said Scott Partridge, Monsanto’s vice president for global strategy.

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The idea is farmers can spray a new, low-volatility version of dicamba on fields of dicamba-resistant crops and kill the weeds without killing the crops, Partridge said. The low volatility makes the substance less likely to drift, he said.

Monsanto calls the new dicamba product Xtendimax with VaporGrip Technology. The EPA has approved the use of Xtendimax on genetically engineered crops, with a number of restrictions. BASF and DuPont also make dicamba herbicides to use with GMO crops.

Other forms of dicamba have long been for sale in Hawaii and are widely available in about 60 products, including Spectracide Weed Stop for Lawns and Ortho Weed B Gon weed killer, the Department of Agriculture’s Seneishi said. Those products are not the subject of recent controversies.

The problem involves dicamba used on farms. As mainland farmers have begun spraying dicamba on growing plants, the herbicide seems to have drifted to nearby fields of crops not engineered to withstand the chemical. By one recent account, government regulators in 17 states were investigating more than 1,400 complaints of dicamba problems covering 2.5 million acres.

The cause of the problems is in dispute, and at the center of a class action lawsuit filed in federal court in St. Louis in July.

It appears Monsanto has used dicamba on GMO soybeans in Hawaii, but the company wouldn’t say how much and when.

Monsanto’s Partridge said it appears many farmers did not follow label instructions for using Xtendimax, which include such details as the type of nozzle to use, the speed and height of the spraying rig, pressure for the tank and size of the buffer zones around the fields. In Georgia, where regulators required training to use the product, Monsanto has gotten no complaints, Partridge said.

But the named plaintiffs in the lawsuit, a group of farmers, contend that Monsanto and the other companies rushed the dicamba-resistant soybeans to market knowing that it was likely farmers would misuse dicamba in ways that might let the chemical drift onto and damage non-GMO crops.

In one instance in Arkansas, one farmer allegedly shot and killed another last year during a dispute over crop damage caused by dicamba.

Plaintiffs Say They Like GMOs

The farmers leading the class action suit against the biotech companies actually extoll the virtues of GMO crops but say the companies were greedy and negligent in the way they rolled out the new products.

“With a global population expected to exceed nine billion by 2050, food production must grow 70% to feed the world,” the complaint says. “While there are some that believe organic or non-GMO crops are a better choice, the math is clear … without GMO crops, there will not be enough food to feed the world.”

“This is not an anti-GMO lawsuit,” the suit adds. “It’s a lawsuit about corporate greed, a rush to market, and the resulting fallout.”

It appears Monsanto has used dicamba on GMO soybeans in Hawaii, but the company wouldn’t say how much and when.

The EPA did not register the new form of dicamba for use in Hawaii, so Xtendimax is not used in the state, said Michelle Starke, science and environmental outreach lead for Monsanto Hawaii. But she said the EPA has approved a dicamba formulation to spray on its seed crops in Hawaii.

Although Monsanto’s Hawaii operations focus mostly on corn, which is naturally resistant to dicamba, the company has grown some dicamba-resistant soybeans, said Starke.

She would not say when Monsanto used dicamba or how much it used, but she said Monsanto would likely use dicamba as it would any other approved agricultural product.

“We, like any other farm, would look at what the needs are out there,” she said.

Starke said Monsanto does not have to spray plants with dicamba to test whether their seeds are genetically resistant to the chemical.

There are no permit requirements to use dicamba in Hawaii, but the state requires companies selling it to register, Saneishi said.

In California, by contrast, farmers need a county permit to use dicamba, said Charlotte Fadipe, a spokeswoman for the California Department of Pesticide Regulation. That means the public can know details of dicamba use.

In light of the recent controversies, Arkansas banned the large-scale sale and use of dicamba, essentially banning it from farms, for 120 days starting July 11.

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Both Arkansas and California allow the sale and use of smaller quantities of dicamba. Arkansas still lets people use dicamba for lawns and gardens, for instance, and in California, there’s no restriction on smaller quantities, such as liquid dicamba sold in containers of a gallon or less and dry formulations packaged in containers of 50 pounds or less, Fadipe said.

Whether Hawaii imposes tighter restrictions depends on the U.S. Environmental Protection Agency, Saneishi said.

“If the EPA restricts it, then we’ll of course follow,” she said.

Norsworthy, the weed scientist from Arkansas, said reports that the EPA is considering banning dicamba have been exaggerated. He said he had been on conference calls with the regulators and it would be hard to infer that the agency is considering a ban.

“That’s an incorrect statement,” he said.

In an email, EPA spokeswoman Amy Graham said the agency is still studying dicamba problems.

“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,” she said. “The underlying causes of the various damage incidents are not yet clear, as ongoing investigations have yet to be concluded.”