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Integration of OMRI-Approved Fungicides, Sanitation, and Cultural Controls for Managing Summer Diseases on Apples 2010

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Project Leaders: David Rosenberger, Professor of Plant Pathology, NY State Agricultural Experiment Station at Geneva and Superintendent of Cornell's Hudson Valley Lab, Highland. Kerik Cox, Assistant Professor of Plant Pathology, NY State Agricultural Experiment Station at Geneva.

Abstract: Experiments were conducted to determine if organic apple growers could minimize losses to summer diseases on apples by using cultural management strategies and/or regular sprays of liquid lime sulfur (LLS). LLS is an OMRI-approved fungicide. Diseases of concern were black rot, flyspeck, and sooty blotch. The latter two diseases appear as dark-colored blemishes on apple fruit surfaces. Although these blemishes do not directly impact edibility, apple with these surface blemishes are not acceptable to fresh fruit buyers. Black rot is a fruit decay that makes fruit inedible, and fruit with black rot can add off-flavors if they are use for juice. During 2010, field trials were conducted in a Jonamac orchard at the Geneva Experiment Station and in a block containing the cultivars Royal Court and Cameo at the Hudson Valley Lab in Highland. Trees in replicated plots received either cultural controls alone, treatment with LLS alone, or a combination of cultural controls and LLS treatments. Cultural controls included removal of fruitlet mummies that can harbor black rot inoculum and hand-thinning of fruit in June followed by light summer pruning to enhance rapid drying following rains and dews and to allow improved spray coverage. Apples were harvested at commercial maturity and evaluated for disease. Both LLS and cultural controls reduced disease incidence and severity of sooty blotch and flyspeck at both test locations, and both approaches reduced the incidence of black rot at Geneva. Neither LLS, cultural controls, nor the combination of the two approaches were consistently effective against black rot in the Hudson Valley where hot humid summers favor this disease. At Geneva, fruit treated with LLS alone or in combination with cultural controls had no more summer diseases than fruit treated with conventional fungicides. However, conventional fungicide programs generally out-performed LLS against summer diseases in the Hudson Valley. This experiment verifies that LLS sprays can be used to control flyspeck and sooty blotch on organic apple farms, but neither LLS nor the cultural controls that we tested will control black rot on cultivars such as Royal Court that are highly susceptible to this disease.