Synthetic and organic fungicide control of apple scab: 2009 field trial
Summary Apple scab, caused by the fungal pathogen Venturia inaequalis, is a significant disease in regions of California characterized by spring precipitation. Disease control is typically attained with periodic application of fungicides. We conducted a field experiment near Camino, California to test the effects of several registered and experimental fungicides on control of scab in mature Red Delicious apple trees. In late spring 2009, following four applications (from green tip into post-bloom), we evaluated disease incidence and severity (lesion density). High disease incidence (>95%) and high lesion density (>12 lesions/fruit) on untreated and water-treated fruits suggested significant disease pressure during the preceding months. Generally, fruits and leaves treated with kresoxim-methyl or mancozeb + flutriafol showed the lowest incidence and severity of disease. Flutriafol (used alone) was moderately effective; tea tree oil, parafinnic oil and monopotassium phosphate (fertilizer) showed little to no ability to control scab.