Using chemical markers to detect root disease in stressed ponderosa pine stands with a low incidence of disease in eastern Oregon

A total of 284 ponderosa pine growing near the southern edge of the Blue Mountains in eastern Oregon were categorized into one of three crown classes based on the degree of “tufted”, or “lion's tail” appearance of their branches, a potential symptom of black-stain root disease, then pushed over and their root systems examined for visual symptoms of disease. Only 23 (8.1%) were found to have more than a trace level of black-stain, annosum root disease, or both at about 38 cm below the root collar. Although there were many measurable differences in crown growth parameters among the three classes, they were not reliable for predicting the presence, or severity of root disease. Differences in crown morphology associated with these classes probably resulted from the combined effects of tree size, levels of resources available on site to support vigorous growth, especially water, and stresses that enhanced water deficits. The sapwood water content of diseased trees was 80.0% of the water content in healthy trees. Acetaldehyde, acetone, methanol, and ethanol concentrations, quantified in the headspace analysis of sapwood collected above the root collar prior to harvest, were all higher in trees with root disease compared to those without disease. Logistic regression models with 0-5 chemical explanatory variables were compared simultaneously by the practical information-theoretic approach to select the best model for predicting trees with root disease. The one selected contained only acetone fresh weight concentrations as an explanatory variable, and would facilitate increased rates of sapwood analysis in the laboratory. More importantly, acetone concentrations may function as useful markers to identify the most severely diseased trees for removal, or in general stand surveys to estimate the level of root disease when symptoms in the crown are lacking or confounded by other stresses.