Propiconazole inhibits Armillaria tabescens in vitro and translocates into peach roots following trunk infusion

Intravascular trunk infusion of propiconazole has been associated with beneficial effects on Armillaria root rot control in Prunus sp. but its basipetal movement has not been verified. Propiconazole, a sterol demethylation inhibitor fungicide, was more effective in inhibiting mycelial growth of Armillaria tabescens isolates in vitro (average effective concentration to inhibit mycelial growth by 50% [EC50 value] of 0.6 mu g/ml) compared with fungicides from five other chemical classes (EC50 values ranging from 4.6 to >1,000 mu g/ml). The fungicide was infused into the vascular system of peach trees in the spring, summer, and fall of 2005 and 2006. Propiconazole concentration was determined using gas chromatography mass spectrometry in trunk sections above and below the infusion site and in primary roots. Over two experimental years, spring and fall infusions resulted in consistent propiconazole accumulations in primary peach roots. Spring infusions yielded propiconazole concentrations of 1.7 mu g/g in 2005 and 5.6 mu g/g in 2006, whereas the highest accumlations were detected following fall infusions with 9.2 mu g/g in 2005 and 6.7 mu g/g in 2006. Propiconazole was also consistently detected in trunk sections collected from above and below the infusion site. The basipetal movement of propiconazole in peach trees and its inhibitory activity against A. tabescens in vitro suggest that propiconazole infusion could be useful for targeted Armillaria root rot management.