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Dr. David N. Appel

Appel, Dr. David N.
Dr. David N. Appel
Professor, Biological Control
Room 413D LF Peterson
Graduate Education
Ph.D. Plant Pathology, Virginia Tech, 1981
Courses Taught
PLPA 301 Plant Pathology
PLPA 626 Diagnosis of Plant Diseases
FRSC 307 Forest Protection
BESC 489 Special topics in Principals of Environmental Regulations

Research Emphasis


Forest Pathology
The following report describes three of the primary activities in the Forest Pathology Lab. The common theme of these activities is improving our understanding of the epidemiology of plant pathogens to make better disease management decisions.

Oak Wilt: The primary components of the project included an infectious forest disturbance (oak wilt, caused by Ceratocystis fagacearum), an indicator of forest health (the endangered avian species, the golden cheeked warbler), and their coexistence in a large tract of Central Texas savannah located within the Ft. Hood Military Installation, TX. The impact of oak wilt on the golden cheeked warbler (GCW) habitat utilizing remote sensing, a Geographic Information System (GIS) and geostatistical analyses is being analyzed. The spatial patterns of disease incidence are related to numerous independent variables using binary decision trees, semivariograms and kriging to create surface maps useful in predicting disease development. These studies will provide landowners and natural resource managers with better information on which to make disease management decisions.

Pierce’s Disease: The epidemiology of Pierce’s disease of grapes depends, in part, on vector behavior, inoculum sources, and the grape cultivars being infected. The colonization of different grape cultivars is being studied in containerized vines by inoculating them with different pathogen strains and assaying for the growth of the bacterium throughout the plants for a year following inoculation. Direct isolation, ELISA, and real time PCR are being used to study colonization and to compare the efficiency of each diagnostic technique. Sequential disease development within different vineyards is being surveyed to study the spread of the pathogen into, and within, vineyards. The spatial patterns of disease incidence and levels of disease severity are being analyzed.

Sudden Oak Death: The SOD pathogen apparently has been disseminated throughout the United States from contaminated nurseries in California during the past 2 years. The Forest Pathology Lab is involved in 3 different surveys within, and around, nurseries in Texas. One of the surveys involve those nurseries receiving plant materials from the contaminated CA nursery (trace forward survey) while the others include a sample of nurseries from throughout the state. Symptomatic plants from regulated host species are being processed the lab using direct isolation, ELISA and PCR to detect the pathogen.


Appel, D.N. 2001. The basics of oak wilt biology and factors influencing disease incidence and severity. Pages 71-81 in, C.L. Ash, ed. Shade Tree Wilt Disease. APS Press, St. Paul. MN. 257 pp.

Appel, D.N. 2001. The use of Alamo for oak wilt management. Pages 101-106 in, C.L. Ash. ed. Shade Tree Wilt Diseases. APS Press, St. Paul, MN. 257 pp.

Everitt, J.H., D.E. Excobar, D.N. Appel, W.G. Riggs, and M.R. Davis. 1999. Using airborne digital imagery for detecting oak wilt disease. Plant Dis. 83:502-505.

McDonald, B.A., Bellamy, B.K., Zhan, J., and Appel, D.N. 1999. The effect of an oak wilt epidemic on the genetic structure of a Texas live oak population. Can. J. Bot. 76:1900-1907.

Watson, W.T., C.M. Kenerley, And D.N. Appel. 2000. Visual and infrared assessment of root colonization of apple trees by Phymatotrichopsis omnivora. Plant Dis. 84:539-543.