Baccharis pilularis, also known as Coyote Bush, is a terrific drought tolerant, California native shrub. Coyote Bush is great for slopes and requires little care once established. This client noticed that her Coyote Bushes started to turn brown at the center of the plant and are slowly dying.
Since only the Coyote Bushes were affected, the probable cause is an insect. The most common type of insect in San Diego that causes this kind of damage is the Flatheaded Borer. Borer insects lay their eggs on the bark of trees and shrubs, especially ones that are weakened by drought. The eggs hatch and then the larvae bore their way into the bark of the plant. This tunneling damages the phloem, or food carrying, section plant. This in turn will slowly kill the plant.
Some borers can be killed with a systemic insecticide. For more information about insects and how to kill them check out the UC Davis Pest Control Webpage;