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Apple Scab Control with Bitertanol as Influenced by Adjuvant Addition. W. F. S. Schwabe, Fruit and Fruit Technology Research Institute, Stellenbosch 7600, South Africa. A. L. Jones, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824. Plant Dis. 67:1371-1373. Accepted for publication 23 June 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1371.

In greenhouse studies, lesion development and conidial production were used to evaluate the curative control of apple scab with bitertanol alone and combined with the adjuvant Agridex. Bitertanol at 62.5 and 125 μg/ml combined with the adjuvant at 250, 500, and 1,000 μl/L prevented most lesion development when applied 2472 hr after inoculation, but when applied 120 hr after inoculation, chlorotic scab lesions were apparent. Because of a higher number of chlorotic lesions, bitertanol alone provided less disease control than when combined with the adjuvant. The adjuvant at 500 and 1,000 μl/L with bitertanol did not improve disease control or inhibition of conidial production over that at 250 μl/L. All curative treatments of bitertanol, either alone or combined with the adjuvant, provided nearly complete inhibition of conidial production. Bitertanol at 62.5 μg/ml plus adjuvant at 250 μl/L (applied 24120 hr before inoculation) provided less disease control than metiram at 1,200 μg/ml. Addition of 600 μg/ml metiram to bitertanol plus adjuvant was highly effective in protecting trees from scab infection for 72 hr.