Department of Plant Pathology

Apple scab, caused by the pathogen Venturia inequalis, is the most important disease affecting apple production throughout the world (MacHardy 1996). In California, the disease impacts orchards in coastal regions, in the Central Valley, and in the foothills of the Sierra Nevada (Ohlendorf 1999). Leaf and fruit infection occurs as V. inequalis ascospores are released from leaf litter (or as conidia are dispersed from tree branches and budscales) in the course of spring rains (MacHardy 1996). A field trial was conducted to evaluate fungicide control of apple scab (Malus x domestica cv Red Delicious) at an orchard near Camino, El Dorado Co., California, in the spring of 2007. The fungicides Procure, Dithane, Sovran, Evito, Endorse, Flint, the organic Champion + Kumulus rotating to JMS Stylet-oil, and the experimental materials A7402 (difenoconazole), Topguard (flutriafol), and LEM17 (penthiopyrad) were compared to an unsprayed control in a completely randomized design. We examined product effects on foliar and fruit scab lesions and evidence for phytotoxicity/russeting on fruit.