The complaints departments of several US state governments have been flooded by submissions from irate farmers, who claim new versions of Monsanto herbicides have caused significant damage to their crops.

The chemical – dicamba – was Monsanto’s bet to replace its line of glyphosate-based herbicides, which were losing their effectiveness as weeds had started developing resistance to them, Reuters wrote on 1 November.

Farmers were claiming that dicamba evaporated and drifted away from its application zones, damaging crops that had not been engineered to resist the herbicide.

According to Monsanto and BASF, which was in the process of acquiring the agrochemicals manufacturer for US$63.5bn, said dicamba was safe when properly applied, but US farmers had failed to follow the detailed 4,550-word instructions on product labels.

Dicamba was previously used to kill weeds before crop planting but, in 2016, the US Environmental Protection Agency (EPA) approved the use of the chemical on dicamba-resistant crops until 9 November 2018.

EPA was scheduled to review the approval extension next year based on consulting and feedback from farmers.

According to Reuters, many of the major soyabean-growing states, including Arkansas, Missouri and Illinois, had each received four years’ worth of complaints about possible damage to crops due to dicamba.

In total, US states had launched 2,708 investigations related to dicamba up to 15 October, according to statistics from the University of Missouri.

Monsanto was hoping to have dicamba-resistant soyabeans account for half of all US soyabean planting by 2019.

The company was also delaying the launch of its NemaStrike pesticide due to reports that it was causing rashes on people, Reuters reported on 2 November.

NemaStrike was intended to combat certain worms attacking corn, soya and cotton and it had undergone extensive evaluation by the EPA before being approved for use, according to Monsanto.

“There have been limited cases of skin irritation, including rashes, that appear to be associated with the handling and application of this seed treatment product,” Brian Naber, US commercial operations leader at Monsanto, said in a letter to customers.

Monsanto attributed some of the cases to improper handling, including not wearing proper safety gear.