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POSTERS: Chemical and Biopesticide Control II

P-090 - Foliar phosphite application may reduce disease progress of butt rot in California almond orchards

Tuesday, August 5, 2025
9:30 AM - 10:15 AM HST
Location: Exhibit Hall 3
Abstract Text: Butt rot, caused by Ganoderma adspersum, is an emerging disease of almond causing tree mortality in California. There are no known disease management strategies. The objectives of the current study were to i) evaluate the efficacy of fruiting body excision as a tool for mitigating disease transmission, and ii) determine the efficacy of phosphite, either applied through chemigation or to the foliage, for suppression of fruiting body regrowth and development of new infections. Disease incidence, rated by presence of fruiting bodies, was evaluated in December 2023 on 16 rows of ‘Nonpareil’ and eight rows each of ‘Monterey’ and ‘Fritz.’ Infected trees were labeled, and fruiting bodies were excised. Fruiting body regrowth was evaluated monthly in 2024. Using a randomized complete block design, K-Phite 7LP was applied as a foliar spray (7 L/ha) to eight rows of ‘Nonpareil;’ eight rows remained untreated. Similarly, four rows each of ‘Fritz’ and ‘Monterey’ were treated with K-Phite 7LP (9.4 L/ha) applied by chemigation; four rows remained untreated.  All phosphite-treated rows were treated in both April and July 2024. Over 70% of fruiting bodies regrew within a year of excision; neither phosphite treatment affected fruiting body regrowth. Chemigation with K-Phite 7LP did not affect disease progress; however, foliar application significantly reduced the development of new incidents of disease. The results suggest that fruiting body excision is unlikely to suppress disease transmission, but foliar K-Phite 7LP application may limit disease progress and thus extend orchard longevity.