Stinkwort made its first California appearance in 1994, but remained quite rare until the mid-2000s, when it began spreading rapidly. Stinkwort is now found in 36 of the state's 58 counties, particularly along roadsides.
"If it gets a major foothold and produces millions and millions of seeds, then the seedlings will grow and they can form a carpet," DiTomaso said. "Then it would block light and prevent the growth of more desirable species – like native plants. It will out-compete them, and that is a concern."
Another troubling aspect is that the weed has been seen in vineyards, said John Roncoroni, UCCE advisor in Napa County, a weed science expert.
"I've seen it on the roadsides in Napa, and it's just encroaching into the vineyards at Napa Valley College," he said.