VIEW ARTICLE

Ecology and Epidemiology

Association of Heterobasidion annosum and the Southern Pine Beetle on Loblolly Pine. S. A. Alexander, Assistant professor, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061; J. M. Skelly(2), R. S. Webb(3), T. R. Bardinelli(4), and B. Bradford(5). (2)(3)(4)(5)Professor, graduate research assistant, former graduate student, and former graduate research assistant, respectively, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061. Phytopathology 70:510-513. Accepted for publication 14 November 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-510.

The association of Heterobasidion annosum and the southern pine beetle (Dendroctonusfrontalis) (SPB) was determined in plantations and in natural, undisturbed stands of loblolly pine (Pinus taeda). Only sites infested with SPB for less than 8 wk were selected for plot establishment. Average incidences of H. annosum in the plantations were 65 and 73%, respectively, for the nine SPB and nine control plots. For the natural stands, average incidences of H. annosum were 24 and 13%, respectively, for six SPB and six control plots. Mean severity levels for H. annosum in SPB and control plots in plantations were 23.1 and 10.9% (P = 0.05), respectively. Mean severity levels for H. annosum in SPB and control plots in natural stands were 12.0 and 0.1% (P = 0.02), respectively. Average percentages of roots colonized in SPB-infested and noninfested trees in the SPB plots were 54 and 11% (P = 0.001), respectively. A significant and consistent association between SPBV-infested loblolly pine and the increased severity of annosum root rot was found on sandy coastal plain soils. Annosum root rot was found to be a major factor in increasing the susceptibility of trees in thinned plantations located on high hazard annosum root rot sites to attack by SPB.