This will really harsh your mellow.

Illicit marijuana farmers in California are using a deadly pesticide — then shipping the tainted tokes off to Midwestern and Eastern states, according to federal authorities.

Researchers this year found 72 percent of illegal pot plantations hidden on public land in the Golden State are using the banned insecticide Carbofuran — and its residue is showing up on 30 percent of plants.

Recreational wacky tabacky use became legal in California this year and the plant has long been grown for “medicinal” purposes in the state, so most of the illegal contaminated crops make their way to other states where the laws aren’t so chill.

Now federal authorities hope to nip the problem in the bud by dedicating $2.5 million to bogarting bootleg farms across the state, officials announced Tuesday.

“What is happening here is illegal for all purposes under anybody’s law,” California US Attorney McGregor Scott told the Associated Press.

Carbofuran, which is smuggled in from Mexico by drug cartels and laborers, is so toxic that just a quarter of a teaspoon can kill a 300-pound bear — and a sixteenth of a teaspoon will get a human wasted for good, according to a Rolling Stone report.

That’s exactly why black-market ganja growers love it so much, experts say: They can quickly and effectively clear public land of critters and they don’t have to carry many canisters in across the border.

“What they are saying to us is this is extremely effective — it takes a little amount to kill a deer or a bear — so we don’t need to bring a lot of it to last a season,” says researcher Mourad Gabriel.

Before doobie-smoking was given the green light in California, officials encouraged stoners to wash their weed in case it was contaminated with Carbofuran, according to the Modesto Bee.

With Post wires