The US Environmental Protection Agency (EPA) is assessing if dicamba herbicide can be sprayed on soyabean and cotton plants genetically engineered to resist the chemical, without posing “unreasonable risks” to other crops, according to an Insurance Journal report.

Farmers and scientists had reported problems with dicamba drifting away from where it was sprayed on fields, causing damage to plants whose genes had not been modified to resist the weedkiller, the 22 December report said.

In 2021, the EPA said it had received about 3,500 reports that more than 404,685ha (1M acres) of non-dicamba-tolerant soyabean crops had allegedly been damaged when the chemical drifted from where it was applied. Trees and crops including rice and grapes also suffered damage.

The number, severity and geographic extent of the incidents were similar to 2020, when the EPA had tightened restrictions on dicamba use following complaints from farmers and scientists about dicamba drifting, the agency said.

“Right now we don’t know whether over-the-top dicamba can be used in a manner that doesn’t pose unreasonable risks to non-target crops and other plants,” Michal Freedhoff, assistant administrator for the EPA’S Office of Chemical Safety and Pollution Prevention said.

The EPA was evaluating all its options for addressing future dicamba-related incidents, he said.

Bayer AG, which sells the herbicide under the name XtendiMax, as well as seeds to grow dicamba-resistant crops, had settled lawsuits brought by landowners who claimed their crops had been damaged by neighbouring farmers using dicamba, Insurance Journal wrote.

Bayer said it believed the EPA’s latest restrictions on use, announced in October 2020, “helped the vast majority of XtendiMax herbicide users succeed with weed control and on-target applications this season [2021].”

Some farmers and seed companies were calling for regulators to limit spraying to before crops were planted, according to the report, with environmental group the Center for Biological Diversity saying the EPA should impose “a complete ban.”

Regulatory changes would probably not be fully implemented by the 2022 growing season, the EPA said, adding that it would work with states that wanted to impose further restrictions.

A US appeals court had blocked dicamba sales in June 2020 ruling that the EPA had substantially understated risks related to its use, Insurance Journal wrote. Four months later, the EPA under former US president Donald Trump had re-authorised the use of dicamba-based weedkillers with new restrictions, invalidating the court ruling, the report said.