Distribution of Heterobasidion irregulare in Missouri pine-oak forests

We surveyed the Missouri Ozarks region for the pathogenic fungus Heterobasidion irregulare, a parasite that has gone largely disregarded within the region since the 1960s despite its potential to cause major problems for the restoration and management of shortleaf pine ( Pinus echinata ). Using spring surveys, we recovered the pathogen (as both spores and basidiomata) at 21 of 31 surveyed sites throughout the extent of the Ozarks region. Using a more intensive spore-trapping procedure, we also surveyed pure hardwood stands within the oak-pine matrix and pure hardwood forests outside the distribution of shortleaf pine. We detected some spores from pure hardwood stands that were relatively near overstory pines, but we detected no spores from pure hardwood forests at long distances (>100 m) from pines. We conducted a GIS-based analysis of pathogen presence and relative spore abundance relative to pine patch distance, pine patch size, and pine patch edge length within the surrounding landscape and determined that distance to the nearest overstory pine as well as the number of pine patches within 500 m were important predictive variables. These data indicate that Heterobasidion irregulare inoculum is likely to be detected within 100 m of overstory pines in the Missouri Ozarks region and demonstrate the ability of this pathogen to persist and spread inoculum even in a landscape with significantly reduced host plant density.