Cystotheca lanestris explained

Cystotheca lanestris, the live oak witch's broom fungus, is a species of mildew that infects buds and induces stem galls called witch's brooms on oak trees in California, Arizona, and Mexico in North America.^{[1] [2]} Witch's brooms are "abnormal clusters of shoots that are thickened, elongated, and highly branched." This fungus infects coast live oaks, interior live oaks, canyon live oaks, valley oaks, and tanoaks, and is most commonly found along the coast. Research published in 2023 newly describes this fungus as also growing in association with Quercus laceyi and Q. toumeyi.^[3]

According to the U.S. Forest Service Treesearch Department:

While this fungus is technically considered a plant disease, most infections are harmless "except possibly in small seedlings".^[4] Cystotheca lanestris is considered widespread in California.

Notes and References

1. Book: Russo, Ronald A. . Plant Galls of the Western United States . Princeton University Press . 2021 . 978-0-691-21340-8 . 2020949502 . 91–92 . en-us . 10.1515/9780691213408.
2. Web site: Live Oak Witches' Broom Fungus (Cystotheca lanestris) . iNaturalist . 2023-10-23 . en-US.
3. Bradshaw . Michael . Braun . Uwe . Quijada . Luis . Coombes . Allen J. . Contreras-Paredes . Carlos . Pfister . Donald H. . 2023-05-04 . Phylogeny and taxonomy of the genera of Erysiphaceae, part 3: Cystotheca . Mycologia . en . 115 . 3 . 427–436 . 10.1080/00275514.2023.2194172 . 37159342 . 0027-5514.
4. A Field Guide to Insects and Diseases of California Oaks . Swiecki . Tedmund J. . Bernhardt . Elizabeth A. . 2006 . U.S. Forest Service Treesearch Department . 10.2737/PSW-GTR-197 . Albany, California . 82 (widespread), 83 (description), 87 (impact on tree health) . Pacific Southwest Research Station . Gen. Tech Rep. PSW-GTR-197.