The US Environmental Protection Agency (EPA) has renewed approval for the use of the controversial herbicide dicamba onto genetically modified (GM) resistant crops.

The herbicide has been credited with damaging thousands of acres of non-dicamba resistant crops due to issues with volatilisation and drift.

The EPA's extension of the use of two dicamba herbicide products comes just days before the US presidential election.

“After reviewing substantial amounts of new information, conducting scientific assessments based on the best available science and carefully considering input from stakeholders, we have reached a resolution that is good for our farmers and our environment,” EPA administrator Andrew Wheeler said.

Drift

Over the past three years, US growers have been dealing with issues relating to new dicamba-tolerant GM soyabean varieties.

When the dicamba active is applied onto the target soyabean plant, it causes that crop no harm, but is highly effective on weeds. However, as the chemical has a high vapour pressure, it’s more likely to evaporate and rise into the atmosphere post-application.

The herbicide has been credited with damaging thousands of acres of non-dicamba resistant crops

When present in the atmosphere, the chemical can drift to "off-target" plants in neighbouring fields which, in many cases, are not dicamba-tolerant. In research published in 2018, dicamba damage was observed over 70 metres away from application sites.

In June, a ruling by the US Court of Appeals for the Ninth Circuit vacated the EPA’s 2017 registration of the products.

The court found that the herbicides drifted from where they were applied and were responsible for damaging crops, including 3.7m acres of nontolerant soyabeans in 2017. It also found that the damage—and resulting harm to farming communities—persisted into 2018.

Restrictions

The EPA will implement new restrictions on dicamba products that will "take care of the drift issues that we have witnessed in the past," Wheeler said.

The court found that the herbicides drifted from where they were applied and were responsible for damaging crops

The new registration requires farmers using XtendiMax and Engenia to add a separate pH buffer to their tank mixes to reduce the volatility of the products.

Both products were originally formulated with low-volatility salts to prevent drift, however thousands of farmers were still effected by drift issues.

Farmers will also have to follow new label instructions, which expand the buffer zone where dicamba can’t be sprayed. The restrictions also prohibit use of the herbicide on soya beans after 30 June and on cotton after 30 July.