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ARS Home » Pacific West Area » Wenatchee, Washington » Physiology and Pathology of Tree Fruits Research » Research » Publications at this Location » Publication #188194
Title: APPLE SCAB MANAGEMENT ASSISTED BY TREE DEFOLIATION WITH VEGETABLE OIL EMULSIONS

Author
item Curry, Eric
item ZU, ZHIGO - SELF EMPLOYED, CHINA
item DOAN, Y - SHANDONG, CHINA

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2005
Publication Date: 10/1/2005
Citation: Curry, E.A., Zu, Z., Doan, Y. 2005. Apple scab management assisted by tree defoliation with vegetable oil emulsions. HortTechnology. 15(4):854-858.

Interpretive Summary: Apple scab, caused by the fungus Venturia inaequalis, is a widespread disease of apple and ornamental crabapple. Without adequate control, it may greatly reduce marketable yield by causing exensive damage to fruit, especially in regions where spring weather is cool and humid. Because previous work indicated vegetable (corn) oil emulsion (VOE) defoliated apple trees within a few days, we evaluated combinations of VOE for tree defoliation, and urea to accelerate leaf decomposition to reducing ascospore population and scab development the following spring. Applied in the fall at 2%, 4% or 6%, VOE induced leaf abscission, with the highest concentration causing the most defoliation. VOE at 4% plus 2% lime sulfur and/or 2% urea applied in late fall defoliated 'Gala' trees effectively and controlled scab on fruit to < 7% the following spring. In the 'Fuji' planting, the combination of 4% VOE plus 2% lime sulfur and 2% urea reduced scab on fruit from 21% in controls to 0%.

Technical Abstract: Vegetable oil emulsion (VOE) was applied to 'Gala' and 'Fuji' apple trees after harvest to induce defoliation and reduce apple scab. Applied in the fall at 2%, 4% or 6%, VOE induced leaf abscission, with the highest concentration causing the most defoliation. At the same concentrations, VOE applied in early, mid, or late Ocrober had similar effects on leaf drop. VOE treatment reduced respiration and stimulated ethylene production in leaf tissue within 24 h of application. None of the treatments affected tree hardiness during the winter, or shoot growth the following spring. Return bloom density was unaffected; however, VOE delayed anthesis by 2 to 4 days. Under controlled conditions, ‘Gala’ and ‘Fuji ’trees inoculated with Venturia inaequalis developed 48% and 65% scab, respectively. VOE-induced defoliation reduced scab by 50% to 65%. VOE-induced defoliation plus leaf removal from the orchard floor, or VOE-induced defoliation in late fall plus application of 5% lime sulfur in early spring controlled scab to < 5% on both leaves and fruit. Neither lime sulfur nor urea applied in late fall at 2% induced defoliation or controlled scab. VOE at 4% plus 2% lime sulfur and/or 2% urea applied in late fall, however, defoliated ‘Gala’ trees effectively and controlled scab on fruit to < 7% the following spring. In the ‘Fuji’ planting, the combination of 4% VOE plus 2% lime sulfur and 2% urea reduced scab on fruit from 21% in controls to 0%.