Update on Diseased and Dying Acacias in the East Bay
On April 1, Matteo Garboletto, extension specialist in forest pathology and adjunct professor at UC Berkeley, released a summary report on the work he and his colleagues have been doing to diagnose the dying acacias in the East Bay hills. The report is available on the Sudden Oak Death website along with lots of other great information for assessing your own trees and shrubs.
Between December 2020 and February 2021, Matteo Garbelotto and his colleagues sampled and analyzed blackwood acacia (Acacia melanoxylon) and some silver wattle (Acacia dealbata) trees at five sites in the Bay Area, including Leona Heights/Montclair and Dimond Canyon in the East Bay. Only two fungi, Diaporthe foeniculina and Dothiorella viticola, were identified at all five sites, and the symptoms the researchers observed on the trees—pie-shaped wood discoloration and stem or branch cankers—are consistent with disease caused by these two fungi.
Both fungi have complex lifecycles. They start as endophytes, living inside trees without obviously affecting tree health, but they often become pathogens when exposed to stress factors like drought, heat stress, fewer foggy days, and competition due to crowding. After an infected tree dies, the fungi continue to live off the wood of the dead tree. Very rainy years, like 2017 in the Bay Area, are known to facilitate fungal infection, and very dry years are known to trigger the shift from endophytic to pathogenic lifestyle.
The April 2021 report includes more detail about the causes of these fungal infections in acacias along with some preliminary management recommendations for acacias in gardens and wildlands and ways to avoid spreading the pathogen to other plant species, including natives.
Matteo Garbelotto and his colleagues are continuing to study the acacia dieoff as well as recent declines in some other East Bay trees and shrubs. Not only is this work important in identifying the cause of serious plant disease and developing management and treatment strategies, but it will also help us understand the fire risk posed by large-scale dieoff events.
On a lighter note, even a drought could not stop the flowers. I enjoyed photographing flowers that were new to me almost every day and am continuing to do so even as the hills turn brown. Of course you can see many gorgeous flower photos on our chapter’s Facebook and Instagram pages as well as the gallery on the CNPS East Bay home page.
– Cathy Chambers, Rare Plant Committee Chair, CNPS East Bay Chapter