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Effects of Pretreatment with Simulated Acid Rain on the Severity of Dogwood Anthracnose. K. O. Britton, Project Leader, USDA Forest Service, Southern Research Station, 320 Green St., Athens, GA 30602. P. Berrang, Biological Scientist, and E. Mavity, Biological Scientist, Southern Research Station, Center for Forest Environmental Studies, Rt. 1, Box 182A, Dry Branch, GA 31020. Plant Dis. 80:646. Accepted for publication 15 February 1996. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1996. DOI: 10.1094/PD-80-0646.

The effects of simulated acid rain on dogwood anthracnose severity were evaluated in a series of greenhouse and field experiments over a 4-year period. In 1990 and 1991, Cornus florida seedlings received 10 weekly foliar applications of simulated rain adjusted to pH 2.5, 3.5, 4.5, and 5.5. They were then placed under mature dogwoods naturally infected with Discula de-structiva. In both years, the percent leaf area infected increased significantly as the pH of the simulated rain solution decreased. In 1992 and 1993, seedlings were wrapped in plastic bags below the root collar to permit separate application of simulated acid rain (pH 2.5) or normal rain (pH 5.5) to the foliage or the growing medium or both. Application of pH 2.5 rain to the growing medium increased disease severity. Foliar applications alone did not increase disease. These results suggest that changes in nutrient availability, rather than foliar damage, are responsible for the increase in anthracnose severity in dogwoods pretreated with simulated acid rain.