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Table: Diagnosis and Control of Apple Scab
Pest Identification Host Plants Damage Symptoms
Apple Scab
Venturia inaequalis
Crabapple trees and apple trees. Some crabapple trees are resistant to apple scab (Adams, David, Liset, red Jewel, and White Cascade). Apple scab causes a spotting of the leaves and fruit. Initial symptoms appear as olive-green spots, which later become velvety. When initial infections are severe, apple scab may also cause premature leaf and fruit drop. Symptoms on the fruit may appear as small necrotic spots or larger lesions that cause deformation of the fruit. The severity of apple scab in any given year will vary depending on the amount of moisture available during the season.
Monitoring Control Options Pesticides
Watch for initial infections to appear shortly after periods of rainfall, early in the spring. It is during this time that spores are being released and new growth is beginning to form. Since apple scab is severe during periods of high humidity and moderate temperatures, monitoring of environmental conditions will help in determining the severity of scab. Once leaves are infected the fungus will continue to spread throughout the tree during periods of wetness. Apple scab should be controlled by a combination of cultural and chemical practices. Cultural practices include sanitation and eradication of infected leaves in the fall as well as infected fruit hanging on the tree. In most cases where apple scab has been present in the past, a chemical spray program including captan, 'home fruit spray', or mancozeb should be conducted. Apple scab spray programs should be started when the leaves begin to emerge and continue according to the label. Captan and 'Home fruit' sprays listed for ornamental crabapples.


Description and Life History
Description: Apple scab is a fungal disease of crabapples that is able to infect leaves, flowers, fruit, and twigs. This disease produces spores in perithecia on fallen leaves and most importantly conidia on infected leaves in the tree.

Life history: Spores produced on infected leaves and fruit, both on the ground and in the tree, infect new healthy leaves in the spring, just as the new growth begins to appear. Once the fungus is established in the tree, it begins to produce secondary spores (conidia) that infect leaves and fruit throughout the tree. Since the spores are only produced during wet periods, the severity of this disease may vary from year to year depending on temperature and rainfall.


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Last modified on March 06, 2013