P-670 - Identification and Management of Fungal Species Associated with Branch Canker and Dieback Disease on Pear (Pyrus communis) in California

California is the leading state of Bartlett pear production, with an annual market value of $117 million. Branch canker and dieback disease of pear are most prevalent near pruning wounds in major pear-producing regions of Northern California. The purpose of this study is to determine the causes of the disease and evaluate management practices. In fall 2023,302 symptomatic branch samples were evaluated through morphological assessments and phylogenetic approaches with three gene regions (ITS,tef1,and tub2).Results showed species of Botryosphaeriaceae,Eutypa lata,Phaeoacremonium minimum,and Kalmusia variispora. The most prevalent are Diplodia malorum,D.seriata,and D.mutila. During dormant pruning,we evaluated the efficacy of biological and synthetic pruning wound protectants against the most prevalent fungal species. Pruning wounds were made on 2–3-year-old branches (n = 4) of ‘Bartlett’ trees in Mendocino County,followed by treatment applications and inoculated 7 days later with 20 µl of 2000 mycelial fragments of the three Diplodia species, respectively. 4 months later, branches were collected,evaluated for vascular discoloration,and isolated on acidified potato dextrose agar to determine pathogen recovery. Preliminary results suggest thiophanate methyl,fluopyram + tebuconazole,and Trichoderma-based products were most effective, reducing the mean percent infection to 2.8%,compared to 33% in untreated controls. Identification and evaluation for managing canker pathogens is crucial to help growers make informed management decisions to reduce infection and improve tree health.