- Pear scab symptoms are found on every part the tree but the trunk. Twigs, leaves, leaf stems, flowers and fruit can all be infected. Initial symptoms on leaves are small brown lesions on the upper surface that eventually become fuzzy and spread to the lower leaf surface. Infected fruit are often deformed and covered in rough brown lesions that are irregular in shape. Twigs and stems develop rough, velvety spots that eventually coalesce into cankerous regions.
- The fungus overwinters in leaf litter on the ground and causes the initial infection in the spring. Rains trigger the release of spores that are spread by wind to twigs and buds. The severity of this initial infection depends on how long spring rains last. The longer they last, the more spores are released into the the air. Secondary infections from fungus overwintering in twig cankers can occur all summer, provided adequate moisture is present for spore release.
- Clean up fallen leaves, twigs and fruit at the end of the growing season to remove any overwintering fungus. Destroy the debris by burning or place it in a landfill-bound trash can. During the dormant season, prune out infected twigs to reduce the chance of secondary infection. Avoid overhead watering, as water triggers the release of spores.
- According to the University of California, fungicide applications are most effective if applied during the dormant season, just before bud break. Lime sulfur or copper fungicides are effective against scab. Additionally, applying a product containing biuret urea just prior to leaf drop in the fall may reduce the amount of overwintering spores in leaf litter. Always read and follow manufacturer's directions carefully when applying chemicals to your trees.
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