The state of California, one of most important for the US agriculture industry, has moved to ban the controversial insecticide active ingredient chlorpyrifos, which some studies have linked to neurological problems in infants and children.

The ban is expected to take full effect in six months to two years.

Chlorpyrifos is sprayed on crops such as oranges, grapes and almonds, and state health officials said there is growing evidence that it can cause serious health effects at lower levels of exposure than previously understood.

California’s new Democratic governor, Gavin Newsom, has proposed $5.7 million to support the transition to “safer, more sustainable alternatives,” according to the state’s Environmental Protection Agency.

In response to a petition from the NGOs Natural Resources Defense Council and Pesticide Action Network North America, US President Barack Obama in 2015 pledged to revoke all food residue tolerances for the chemical nationwide. This proposal was overturned by the incoming Trump administration before it could take effect, however.

“By reversing the previous administration’s steps to ban one of the most widely used pesticides in the world, we are returning to using sound science in decision-making rather than predetermined results,” incoming EPA Administrator Scott Pruitt said.

Reports persisted that then-Dow Chemical CEO Andrew Liveris, who campaigned with Trump and headed his US Manufacturing Council before it was disbanded, may have whispered in the administrator’s ear.

The EPA’s backtracking was short-lived, as in August 2018 a US appeals court ordered the agency to halt sales of chlorpyrifos-containing products within 60 days. This decision was immediately appealed, and its implementation is still on hold.

While the agency’s current leadership came in for criticism in the ruling, the judge commented that over the past two decades the EPA’s own scientists had documented the possible adverse effects of chlorpyrifos without any action being taken.

DowDuPont, which manufactures the product developed by Dow, has pledged to fight the grower state’s ban, saying it would “remove an important tool for farmers and undermines the highly effective system for regulating pesticides that has been in place at the federal level and in the state of California for decades.” The state is the top US user.

“This proposal disregards a robust database of more than 4,000 studies and reports examining the product in terms of health, safety and the environment,” said the merged group, whose new agrochemicals arm, Corteva, will start business on Jun. 1.

With the EPA now rolling back more regulations than it creates, US states are increasingly adopting their own environmental legislation. In 2018, Hawaii became the first to ban products containing chlorpyrifos, starting from 2022. New York will have a ban in place by the end of 2021. Oregon, Connecticut and New Jersey also have bills to remove products containing chlorpyrifos from the market.

On their own, other states have ordered manufacturing companies to remove fluorochemicals from waterways or have begun regulating greenhouse gas emissions, and the patchwork of differing regulations has created uncertainty at businesses operating in more than one state. Most of the firms support national standards.

While newly confirmed EPA administrator Andrew Wheeler has encouraged states to make their own rules – in an effort to appease small government advocates, he has insisted that he would oppose moves that could interfere with national commerce.