Denver Tree Diseases

Disease	Description	Treatment Calendar	Photo
Anthracnose	Several species attack trees such as Sycamore, Ash, and Maple causing significant stress and potential death.	March – June
Cytospora Canker	Bacterial disease that affects aspen, cottonwood, mountain ash, spruce and others. Very difficult to control.	March – April & June – July
Dutch Elm Disease	Although not as prevalent as in the 70’s and 80’s, Dutch elm disease is can be terminal to American elm trees. Fungus carried by elm bark beetle. Preventative treatments effective.	April – July
Fireblight	A very aggressive bacterial disease that attacks Apple, Crab-apple, Pear, Peach, Mountain Ash and Hawthorn. Treatable with ArborJet.	March – August
Gummosis	A form of Cytospora Canker, gummosis attacks peach, cherry, apricot and plum. Very destructive.	March- April & June- July
Powdery Mildew	A fungal disease which infects leaves of trees and shrubs such as Apple, Lilac and Roses. Leaves will have a light powdery look. Fungicide applications can help.	March – April
Thyronectria Canker	A fungal disease that kills the living bark and outer wood of honeylocusts.	No Control
1000 Canker Disease	A terminal disease for walnut trees. Vectored by the walnut twig borer.	Late Summer