The county parks department signs will urge visitors to:
Park in designated areas.
Stay on established trails and avoid mud.
Don't collect and transport wood, soil or plants.
Clean off hiking shoes, bike wheels, horse hooves and dog paws.
Wash off mud on car's tires, wheel wells and undercarriage at the nearest automated car wash.
The tree-killer, a relative of the fungus that caused the great potato famine in 19th-century Ireland, girdles a tree, destroys its cell walls and disrupts the flow of nutrients. California's tanbark oaks, coast live oaks and black oaks are most severely affected.