Check out yellow leaves on rhododendrons and azaleas.
A list of recommended trees and shrubs in Oregon, good for controlling erosion.
Excessive summer irrigation of oak and madrone trees may promote fungal diseases such as the oak root fungus (aka armillaria root disease) and crown rot.
Organic pesticides are usually considered as those pesticides that come from natural sources. They are usually minimally processed. These natural sources are usually plants or minerals. There are also microbial pesticides.