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Disease Note.

Enhancement of Discula sp. Infection of Flowering Dogwood (Cornus florida) by Pretreating Leaves with Acid Mist. R. L. Anderson, USDA Forest Service, FPM, Route 3, Box 1249A, Asheville, NC 28806. J. L. Knighten, and S. Dowsett. USDA Forest Service, FPM, Route 3, Box 1249A, Asheville, NC 28806. Plant Dis. 73:859. Accepted for publication 7 July 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0859D.

Dogwood anthracnose, caused by Discula sp., has spread rapidly across the South in recent years, causing heavy mortality in some areas. Spraying of pure cultures has provided leaf symptoms (1), but results at other locations have been inconsistent. In an attempt to consistently induce infection by conidia from cultures of Discula sp., we applied three treatments to I-yr-old seedlings of C. florida: 1) water (pH 7) mist only (control) on four consecutive days; 2) water mist on days I and 3, spore mist on days 2 and 4; and 3) mist with water adjusted to pH 2.8 with HCl on days I and 3, spore mist in pH 7 water on days 2 and 4. Each seedling was placed in a plastic bag and held in a head house. Leaf and stem symptoms occurred only on plants receiving acidified mist plus spores. Leaf spots developed in 7 days and leaf blotch and shoot blight, in 14 days. Discula sp. was recovered from all symptomatic tissues. The study was repeated with the addition of an acid mist control; again, symptoms of Discula sp. infection developed only after the acid/spore treatment. These results suggest that acid mist may predispose C. florida to Discula sp. infection.

Reference: (1) C. R. Hibbin and M. L. Daughtrey. Plant Dis. 72:199, 1988.