Previous View
 
APSnet Home
 
Phytopathology Home


VIEW ARTICLE

Ecology and Epidemiology

Measurement of Expanding Oak Wilt Centers in Live Oak. D. N. Appel, Associate professor, Department of Plant Pathology and Microbiology, Texas A&M University, College Station 77843; R. C. Maggio(2), E. L. Nelson(3), and M. J. Jeger(4). (2)Associate professor, Department of Forest Science, Texas A&M University, College Station 77843; (3)Graduate research assistant, Computer Science Department, Texas A&M University, College Station 77843; (4)U.K. Overseas Development Natural Resources Institute, London, U.K. Phytopathology 79:1318-1322. Accepted for publication 28 July 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1318.

Local, tree-to-tree spread of Ceratocystis fagacearum was monitored in live oak (Quercus fusiformis) with sequential, color infrared aerial photography during 1982–1987. A computer-based system for analyzing expanding foci was developed to measure rates of crown defoliation and mortality, as well as expansion distances. Four foci expanded radially an average of 11–16 m/yr, with longer maximum distances of expansion (up to 40 m/yr) commonly occurring. One focus that expanded most rapidly increased from 0.3 to 3.6 ha over 5 yr, affecting 10,774 m2 of crown cover. This was initially the smallest focus, and it had the greatest live oak density. The largest initial focus had a lesser oak density and increased from 1.5 to 6.6 ha, affecting 11,396 m2 of crown cover. Crown survival in 1987 ranged from 4 to 26% for trees that originally showed symptoms in 1982. A strong linear correlation between the area of affected crown cover and total area occupied by each focus was noted. The rapid rates of focus expansion were attributed to a high potential for root grafting and the occurrence of common root systems among clonally propagated live oaks.

Additional keywords: Ceratocystis fagacearum, epidemiology, Quercus fusiformis.