Published on 26/09/2025
It’s used pre-emergence to control wireweed in vegetable crops.
Last year, the EPA imposed restrictions on the chemical due to significant concerns about its effects on foetal development. This followed an emergency suspension order issued by the US Environmental Protection Agency.
Independent economic research found agricultural use of chlorthal-dimethyl was already fairly low, EPA says.
Information from chemical suppliers shows about two-thirds of NZ growers have turned to using alternative products that are readily available and cheaper.
Among products containing chlorthal-dimethyl, Chlor-Back 75 WG is the only one currently registered under the Agricultural Compounds and Veterinary Medicines Act. Dacthal and Deramot Xtra have been de-registered since the temporary restrictions were imposed.
The chemical is now banned in Australia, Canada, the European Union and the United States.
“We analysed the toxicological studies, and these confirmed the potentially harmful effects of chlorthal-dimethyl,” says Dr Shaun Presow, acting hazardous substances applications manager.
“Evidence indicates that chlorthal-dimethyl presents risk primarily to pregnant bystanders, or pregnant workers who work with chlorthal-dimethyl, or those who enter treated fields after the substance has been applied.”
For anyone pregnant and exposed to the chemical, the endocrine effects could harm the development of the foetus and lead to significant impacts on offspring.
“Even the strictest application controls, such as wearing respirators and gloves during spraying, will not sufficiently protect pregnant workers.
“Our research of the data also showed that there is a risk of chlorthal-dimethyl contaminating groundwater regardless of controls put in place,” says Presow.
“If revoked, all herbicide approvals containing chlorthal-dimethyl as an active ingredient would no longer be approved under the HSNO Act and banned for import and manufacture in NZ.”
The ban would come into effect immediately, and we would then propose a six-month period for disposal of existing stock.