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Ask the Arborist: Anthracnose Leaf Loss

Question: My Ash tree lost all of its leaves last spring.  It put out new leaves but has looked terrible all summer.  What can I do to prevent this from happening again next year?

Answer: Your Ash was infected by anthracnose, an infection caused by any of several fungi, depending on the species of tree attacked.  Sycamore, Ash, Dogwood and Chinese Elm are particularly susceptible to this disease.  Infections are more severe when prolonged spring rains occur after new growth is produced.  Infected leaves fall prematurely and throughout the growing season, and sometimes trees are completely defoliated. 

Once symptoms develop or become severe they cannot be reversed in the same year but they can be prevented from recurring, or at least limited, in the following year. Rake and dispose of fallen leaves and twigs during the growing season and in the fall.  Prune during winter to increase air circulation in the canopy and remove the previous seasons infected twigs and branches.  To stimulate growth of trees severely affected by anthracnose, fertilize after the leaves open and spring rains have stopped. 

Foliar fertilizer sprays are not effective if the rains continue.  As an alternative to foliar sprays on a highly valued tree, trunk injections in the fall with a systemic fungicide, Alamo, will protect next year’s leaves.


Live Oak The Atherton Tree Committee is a volunteer, non-profit, community based organization dedicated to the preservation of Atherton's heritage trees. The committee participates in a variety of programs designed to educate residents about the value of trees in our environment and to encourage appreciation and protection of our urban forest resources. For more information about town ordinances, policies, inspections, and plan reviews contact the Atherton Town Arborist, Sally Bentz (650-752-0526, or link to the Town of Atherton Web Site. For more information about the Tree Committee contact Denise Kupperman (650-704-1693,