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Anthracnose Infection of Dogwood Seedlings Exposed to Natural Inoculum in Western North Carolina. K. O. Britton, Research Plant Pathologist, USDA Forest Service, Southeastern Forest Experiment Station, Athens, GA 30602. . Plant Dis. 77:34-37. Accepted for publication 9 September 1992. 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, 1993. DOI: 10.1094/PD-77-0034.

Groups of 25 healthy dogwood seedlings were exposed for 2 wk to naturally occurring inoculum under mature, diseased trees at 2-wk intervals for three growing seasons. After exposure, seedlings were placed in an incubation room and supplied with trickle irrigation and fluorescent lighting for 2 wk. Following incubation, percent leaf area infected (LAI) was estimated visually. In 1989, LAI remained less than 5% until June. However, consistent rainfall throughout the summer created conditions conducive to infection of seedling groups exposed from 6 June through September, and LAI ranged from 11 to 47% during that period. In 1990 and 1991, LAI was less than 5% until early May, and heavy infection began in mid-May. Midsummer droughts reduced LAI to less than 5%. LAI increased with renewed rainfall but dropped below 10% for the remainder of the season beginning in mid-July 1990 and in September 1991. Numerous secondary infection cycles occurred in each of the 3 yr. Stepwise regression analysis showed that 34% of the variance in LAI was explained by 2-wk rainfall total and 17% was explained by the LAI of the previous seedling group. This supports the hypothesis that secondary infection cycles in southwestern North Carolina depend on consistently recurring rainfall and inoculum buildup.

Keyword(s): Cornus florida, dieback, Discula destructiva Red.