{"id":34837,"date":"2026-06-02T22:57:04","date_gmt":"2026-06-03T02:57:04","guid":{"rendered":"https:\/\/extension.umaine.edu\/publications\/?page_id=34837"},"modified":"2026-06-03T14:33:03","modified_gmt":"2026-06-03T18:33:03","slug":"2381e","status":"publish","type":"page","link":"https:\/\/extension.umaine.edu\/publications\/2381e\/","title":{"rendered":"Bulletin #2381, Management of Sphaerulina Leaf Spot, Leaf Rust, and Powdery Mildew"},"content":{"rendered":"\n

By Seanna Annis, PhD., Extension professor and professor of mycology, University of Maine and University of Maine Cooperative Extension and Leala Machesney, wild blueberry Extension and research professional, University of Maine Cooperative Extension<\/em><\/p>\n\n\n\n

For information about UMaine Extension programs and resources, visit extension.umaine.edu<\/a>.<\/strong>
Find more of our publications and books at extension.umaine.edu\/publications\/<\/a>.<\/strong><\/p>\n\n\n\n

Introduction<\/strong><\/h3>\n\n\n\n

Sphaerulina leaf spot, leaf rust, and powdery mildew are the three most common leaf spot diseases found in wild blueberry fields. All three can reduce the amount of leaf area that plants can use for photosynthesis by causing plants to shed, or \u201cdrop,\u201d leaves. We sometimes see early leaf drop in July, but not every year or in every field. Whether a leaf will be dropped depends primarily on how old it is and how much light it is getting. Older leaves at the bottom of the stem are likely to be lost due to normal processes, because these leaves will be the least productive in photosynthesis. Other factors impacting leaf loss are the amount of leaf tissue affected by leaf spots (more heavily infected leaves are less productive) and drought, which puts the plants under more stress, so they may lose the least productive leaves to save water.<\/p>\n\n\n\n

Sphaerulina Leaf Spot<\/strong><\/h3>\n\n\n