Propiconazole distribution and effects on Ceratocystis fagacearum survival in roots of treated red oaks

We investigated the interaction between the oak wilt pathogen (Ceratocystis fagacearum) and propiconazole in lower stems and roots of Quercus rubra to better understand published reports of fungicide failure after 2 years. Propiconazole was infused into mature oaks in July 2004 and roots were inoculated with pathogen endoconidia 1.0 m from injection sites at ±2 weeks of fungicide treatment. Pathogen presence in wood samples was determined by isolation and fungicide concentrations measured using gas chromatography-mass spectrometry. Propiconazole was detected in the roots (<1.0 m from injection sites) of all treated trees at 2, 12, and 24 months. Propiconazole was detected in all samples (n =68) at 2 and 12 months and in 93% of samples (n = 72) at 24 months with concentrations ranging from 815 ppm (12 months in lower stem) to 0.7 ppm (24 months in most distal root segment). Although pathogen isolation incidence was lower in treated than disease control trees at 2 and 12 months, at no time did an infused oak fail to yield the fungus upon isolation. The results document basipetal movement and degradation of propiconazole, as well as the survival of the pathogen, over time in roots and lower stems of infused red oaks.