Many marijuana growers in states that have legalized recreational or medical marijuana use pesticides, without any federal regulations, according to NPR.

While the federal government tells farmers which pesticides are safe, it has not issued rules on pesticides for marijuana. The drug remains illegal under federal law.

As a result, growers are experimenting with little oversight, according to Colorado State University entomologist Whitney Cranshaw. “In the absence of any direction the subject of pesticide use on the crop has just devolved to just whatever people think is working or they think is appropriate,” he said.”Sometimes they’ve used some things that are inappropriate, sometimes unsafe.”

Brett Eaton, a plant expert with American Cannabis Company, a Denver-based consulting group, says pesticides can harm the product as well as the consumer. “Anybody can get their hands on harmful chemicals, and they can just spray away all the way up until the last day of harvest,” he said.

In Denver, officials placed a hold on tens of thousands of marijuana plants earlier this year, due to safety concerns. While Colorado does not require growers to test marijuana for traces of pesticides before selling it, state agriculture officials recently released a list of pesticides considered appropriate for use on marijuana. Similar lists have been released by Washington state, Nevada and Illinois.

“Other agricultural industries already have policy in place for the safe use of spraying certain pesticides and fungicides,” Eaton said. “This being a new industry, it hasn’t been addressed yet.”