SACRAMENTO — Researchers and federal authorities are finding what they say is an alarming increase in the use of a powerful pesticide at illegal marijuana farms hidden on public land in California.

The pesticide residue is showing up in about 30 percent of the plants themselves, researcher Mourad Gabriel said.

Most of the illegally grown California pot is destined for Midwestern and Eastern states, federal prosecutors said. Federal and state authorities are announcing Tuesday that they will target the illegal grows with $2.5 million in federal money.