Farmers of soybeans and other crops in southeast Missouri, western Tennessee and northeastern Arkansas are facing widespread crop damage believed to be the result of illegal spraying of dicamba, an older herbicide that is finding new life as a tool to battle glyphosate-resistant weeds.

In four Missouri Bootheel counties alone, more than 100 complaints of pesticide drift have been reported since June 22, said a representative from the Missouri Department of Agriculture. For comparison, the department typically receives 75 to 80 complaints statewide in an entire year. Experts say all signs point to dicamba as the culprit behind the surge.

�The symptoms match what we would expect coming out of dicamba,� said Kevin Bradley, an associate professor in the University of Missouri�s division of plant sciences and a lead scientist for the university�s agricultural extension. Possible exposure to the herbicide has been officially reported on 40,000 acres of soybeans in the state, causing the plants� leaves to pucker and potentially hurting yields across the region.

State investigations into each complaint are ongoing, but many suspect the problem stems from farmers who have planted Roundup Ready 2 Xtend soybeans � a dicamba-resistant crop variety released this year by Creve Coeur-based Monsanto Co. But the dicamba-based herbicide meant to be applied to Xtend seeds has not been approved by the Environmental Protection Agency, leaving farmers without the tool intended to fight increasingly stubborn weeds that have developed resistance to other herbicides such as Roundup, which has glyphosate as its active ingredient.

Even without the corresponding herbicide, Monsanto began releasing the seeds because the company says they offered farmers attributes � such as improved yields � beyond dicamba tolerance. Monsanto officials reported that seeds for 1 million acres of soybeans have been sold with the technology this year, along with 3 million acres of cotton, introduced in 2015.

Some farmers, it appears, have taken matters into their own hands, spraying other forms of dicamba that are unauthorized for use with Xtend crops. This alleged �off-label� use of the herbicide leaves dicamba-resistant plants unharmed but can drift into neighboring fields, either when blown by wind or when liquid particles turn to gas and spread as vapor.

�It basically boils down to the fact that you have a very sensitive crop in soybeans planted in close proximity to crops that are a GMO,� or genetically modified organism, �that is able to withstand dicamba,� Bradley said. �And some people made dicamba applications, allegedly, and hurt people�s crops.�

Even low dicamba concentrations measuring in parts per million can damage non-GMO varieties of soybeans. That sensitivity has led companies such as Monsanto to seek less volatile forms of the herbicide that do not vaporize as easily.

Monsanto said the Xtend-compatible dicamba still seeking approval offers that lower volatility than dicamba alternatives currently on the market. But in its absence, drift from suspected �bad actors� knowingly using unapproved substitutes is taking its toll.

Although dicamba damage can be seen visually, its ultimate effect on yields won�t be known until harvest. Whatever its impact, insurance companies have indicated they will not compensate farmers for losses related to wrongful dicamba use.

�That still doesn�t keep a person from suing personally, and I�m afraid that�s what�s going to happen,� said Terry Weaver, a farmer near Holcomb, speculating on how some victims might resort to litigation to recover losses. But linking diminished yields directly to dicamba � and to a specific wrongdoer � could be difficult.

�The problem with dicamba is it travels so easily and so far that it�s hard to pinpoint where it actually came from,� said Kade McBroom, a farmer and the operator of Malden Specialty Soy, a processing facility for non-GMO soybeans in the area. �That burden of proof can get kind of tricky.�

Many farmers have said there are not sufficient penalties in place to deter illegal use of herbicides, likening the current $1,000 fine � enforced by the state Department of Agriculture � to a slap on the wrist.

�If the speeding ticket�s $5, why worry about it?� Weaver said. �If they get a clean field, that�s a whole lot cheaper than getting it clean with hand-hoeing.�

While calling the behavior �selfish,� Weaver said illegal dicamba application was a predictable outcome when farmers can spray a field for a fraction of the cost that it would take to manually remove Roundup-resistant nuisances such as pigweed.