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Factors Affecting Infection of Water Oak, Quercus nigra, by Tubakia dryina . Y. C. Zhang, Plant Pathologist, Shanxi Forestry Research Institute, Taiyuan P.R. of China. J. T. Walker, Professor, Department of Plant Pathology, University of Georgia, Georgia Station, Griffin 30223-1797. Plant Dis. 79:568-571. Accepted for publication 15 March 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0568.

Tubakia dryina is commonly associated with leaf spots of water oak growing in the Piedmont of Georgia. The fungus was isolated from leaves, buds, or twigs collected from symptomatic trees from October 1991 through August 1992. The greatest isolation frequency (82 to 92%) occurred on leaves sampled in June, July, and August; a lower frequency (29 to 62%) was obtained for spring and fall months. Conidia! germination on 2% water agar occurred from 10 to 35C with maximum germination between 20 and 30C after 24 h. The disease severity ratings of inoculated excised leaves and leaves on trees in the field increased with time and developed at a somewhat faster rate later in the season. Leaves on 1 -year-old water oak seedlings, growing in soil treated with diuron + imazapyr at less than recommended rates, developed more severe disease when inoculated with T. dryina than seedlings treated with each herbicide alone or no herbicide

Keyword(s): Actinopelte, Tubakia leaf spot