Measurement of Expanding Oak Wilt Centers in Live Oak

Abstract

Appel, D. N., Maggio, R. C., Nelson, E. L., and Jeger, M. J. 1989. Measurement of expanding oak wilt in live oak. Phytopathology 79:1318-1322. Local, tree-to-tree spread of Ceratocystis fagacearum was monitored live oak density. The largest initial focus had a lesser oak density and in live oak (Quercus fusiformis) with sequential, color infrared aerial increased from 1.5 to 6.6 ha, affecting 11,396 m 2 of crown cover. Crown photography during 1982-1987. A computer-based system for analyzing survival in 1987 ranged from 4 to 26% for trees that originally showed expanding foci was developed to measure rates of crown defoliation and symptoms in 1982. A strong linear correlation between the area of affected mortality, as well as expansion distances. Four foci expanded radially crown cover and total area occupied by each focus was noted. The rapid an average of 11-16 m/yr, with longer maximum distances of expansion rates of focus expansion were attributed to a high potential for root (up to 40 m/yr) commonly occurring. One focus that expanded most grafting and the occurrence of common root systems among clonally rapidly increased from 0.3 to 3.6 ha over 5 yr, affecting 10,774 m 2 of propagated live oaks. crown cover. This was initially the smallest focus, and it had the greatest Additional keywords: Ceratocystisfagacearum, epidemiology, Quercusfusiformis. Oak wilt centers are classical examples of disease foci, or in live oak; and to facilitate the placement of barriers for disease local concentrations of diseased plants about primary sites of control. This report describes the system and illustrates some infection (10). As defined, the size and shape of foci tend to important aspects of oak wilt epidemiology in Texas. influence patterns of further spread. Contaminated insects (Coleoptera: Nitidulidae) initiate foci in new areas by acquiring