When actress René Russo appeared in a video (posted below) about “New Oak Threats,” she wasn’t acting. The veteran of big-budget thrillers like Lethal Weapon 3 and 4 and the Thomas Crown Affair expressed her personal convictions when she called for Californians to become educated and observant guardians of California oaks.

“I love our beautiful oak trees,” Russo said. “But there’s a new pest in town, and we could potentially lose every tree that we have. It would change the face of Southern California. It’s terrifying.”

The actress says the death of 80,000 oak trees in San Diego County since 2008 from...