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Factors Affecting Control of European Apple Canker by Difolatan and Basic Copper Sulfate. H. J. Dubin, Research Assistant, Department of Plant Pathology, University of California, Davis 95616; Harley English, Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 64:300-306. Accepted for publication 17 July 1973. DOI: 10.1094/Phyto-64-300.

Oil enhanced the toxicity of basic copper sulfate (BCS) to Nectria galligena conidia at copper concns between 10⁰ and 10² µg/ml but reduced toxicity at 10³ µg/ml as measured by germination inhibition. The effect was not observed with respect to inhibition of germ tube elongation. Difolatan was fungitoxic in vitro at 1.0 µg/ml. In field spray tests, Difolatan 4 Flowable 2.8 liters/378.5 liters (3 qt/100 gal) reduced conidial and perithecial production but BCS 2.3 kg + 1.9 liters Supreme oil/378.5 liters (5 lb + 2 qt/100 gal) decreased only perithecium production. Both fungicides were retained on the trees for the 12-wk leaf fall period but only Difolatan was redistributed in fungitoxic amounts. Three wk after spraying, Difolatan apparently had increased on twigs whereas it had decreased on leaves. The less retentive leaves served as a temporary reservoir for Difolatan. The copper in deposits of BCS decreased linearly with time and rainfall. Bioassays showed that Difolatan totally inhibited conidial germination during the normal infection period but inhibition on BCS-sprayed trees decreased rapidly with time.