Efficay of foliar applications of a phosphite fungicide for control of apple scab, caused by Venturia inaequalis
M. ELLIS (1), W. Stringfellow (2), L. Wilson (1). (1) Ohio State University, Wooster, OH, U.S.A.; (2) Quest Products Corp., Lindswood, KS, U.S.A.
Phosphite fungicides have been shown to be effective in controlling diseases caused by oomycetes, as well some fungal plant pathogens. We have studied the efficacy of foliar applications of the phosphite fungicide AGRI-FOS for control of apple scab, caused by <i>Venturia inequalis</i>. Dilute foliar applications of the product were made with a hand gun to McIntosh and Delicious apple trees at the rate of 1.89 L per 378.5 L of water. Trees were sprayed until foliage was wet. Treatments were applied in a 7-day standard protectant program, in a curative program applied at 24, 48 and 72 hours after the initiation of an infection period, and in an extended protectant program in combination with Captec fungicide at 0.95 L per 378.5 L of water. Treatments were applied from 12.7 mm (0.5 inch) green through first cover. All treatments received cover sprays of Captec at 7 L per ha on a 14-day schedule starting at second cover for the remainder of each season. All treatments and programs provided good to excellent control of apple scab compared to the non-treated control. Incidence of primary scab for the foliar application in 2008, 2009 and 2010 on McIntosh was 3, 2, and 2% for treated trees, and 96, 92 and 79% for the untreated control. Curative treatments provided a significant level of scab control when applied up to 72 hours after infection. The extended protectant program also provided excellent control of primary scab in 2 years of testing.
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