The effect of post-harvest foliar urea applications on tree healthand ascospore production of Venturia inaequalis


Abstract: Apple scab, caused by Venturia inaequalis, is typically managed by applying frequentapplications of fungicides to prevent infection by ascospores, the only significant source ofprimary inoculum. This study investigated the use of single and split post-harvest applications of5% urea on ascospore production and the effects on tree health. In 2007, 2008, and 2009,naturally infected ‘Cortland’ leaves were sprayed by hand with urea to (1) determine the mosteffective time of application to reduce the production of ascospores and (2) determine if two2.5% and three 1.6% split applications of urea were more effective than a single 5% ureaapplication. Treated and untreated leaves were overwintered on the orchard floor and in thespring ascospores were collected onto slides using a volumetric spore trap in order to calculateascospore production. All urea treatments significantly reduced ascospore production comparedto an untreated control. Split applications of two 2.5% urea were more effective at reducingascospore production than a single 5% application made immediately post-harvest. The sameurea treatments were applied with an air blast sprayer to ‘Marshal Mac’ trees in 2007, 2008, and2009 to determine their effects on winter injury, fruit set, foliar nitrogen content, and extensionshoot length. The urea treatments had no adverse effects on winter injury, fruit set, and foliarnitrogen content.

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