With the turn of the calendar to June, farmers in the U.S. Midwest are wrapping up the planting of new soybean crops and tending to growing fields of young corn plants and vegetable plots. But many are also bracing to be hit by an invisible enemy that has wreaked havoc in farm country the last few summers – the chemical weed killer dicamba.

Jack Geiger, a certified organic farmer in Robinson, Kansas, describes the last few summer growing seasons as characterized by “chaos,” and said he partially lost certification for one field of organic crops due to contamination with dicamba sprayed from afar. Now he is pleading with neighbors who spray the weed killer on their fields to make sure the chemical stays off his property.

“There is dicamba everywhere,” Geiger said.

Geiger is only one of hundreds of farmers around the U.S. Midwest and several southern states who have reported crop damages and losses they claim were caused by drifting dicamba over the last few years.

Farmers have been using dicamba herbicides for more than 50 years but traditionally avoided applying the herbicide during hot summer months, and rarely if ever over large swaths of land due to the well-known propensity of the chemical to drift far from intended target areas.

That restraint was reversed after Monsanto launched dicamba-tolerant soybean and cotton seeds to encourage farmers to spray new formulations of dicamba “over the top” of these genetically engineered crops. Monsanto, which is now owned by Bayer AG, along with BASF and Corteva AgriScience all gained approval from the Environmental Protection Agency (EPA) to market new formulations of dicamba herbicides for spraying over the tops of growing dicamba-tolerant crops. The companies claimed their new versions of dicamba would not volatize and drift as older versions of dicamba weed killing products were known to do.

But those assurances have proven false amid widespread complaints of dicamba drift damage since the introduction of the new dicamba-tolerant crops and the new dicamba herbicides.

A consortium of farmer and consumer groups sued the EPA over its backing of the over-the-top use of the dicamba herbicides and is now awaiting a ruling by the ninth circuit court of appeals in San Francisco regarding their demand that the court overturn the EPA’s approval of the three company’s herbicides. Oral arguments were held in April.

The consumer and environmental groups allege the EPA broke the law by failing to analyze the “significant socioeconomic and agronomic costs to farmers” leading to “catastrophic” levels of crop damage.

The groups say the EPA seems more interested in protecting the business interests of Monsanto and the other companies than in protecting farmers.

Lawyers for Monsanto, representing the company as a unit of Bayer, said the plaintiffs have no credible argument. The company’s new dicamba herbicide, called XtendiMax, “has assisted growers in addressing a significant nationwide weed resistance problem, and soybean and cotton yields have hit record highs nationwide during this litigation,” according to a brief filed by the company’s lawyers on May 29.

“Petitioners’ request for an order immediately halting all sales and uses of the pesticide invites legal error and potentially disastrous real-world impacts,” the company said.

As they await the federal court’s decision, farmers are hoping that new restrictions put in place by some states will protect them. The Illinois Department of Agriculture has advised applicators that they can’t spray after June 20, that they should not spray dicamba products if the temperature is over 45 degrees Fahrenheit, and that they should only apply dicamba when the wind is blowing away from “sensitive” areas. Minnesota, Indiana, North Dakota and South Dakota are among other states putting in place cut-off dates for spraying dicamba.

Steve Smith, director of agriculture at Red Gold Inc, the world’s largest canned tomato processor, said even with the state restrictions he is “extremely concerned” about the upcoming season. More acres of being planting with the dicamba-tolerant soybeans developed by Monsanto so it is likely there will be more dicamba being sprayed, he said.

“We’ve worked hard to keep the message out there of not to get close to us, but someone, sometime, is going to make a mistake that could seriously cost us our business,” he said.

Smith said he is hopeful the court will overturn the EPA approval and “stop this insanity of a system.”

Separately from the potential dicamba damage to crops, new research was recently published showing that farmers exposed to high levels of dicamba appear to have elevated risks of liver and other types of cancer. Researchers said the new data showed that an association previously seen in the data between dicamba and lung and colon cancers was “no longer apparent” with the updated data.