Persistence of Propiconazole in Peach Roots and Efficacy of Trunk Infusions forArmillariaRoot Rot Control

Abstract

Trunk infusion of peach with propiconazole has been suggested as a potential strategy to protect roots from colonization by Armillaria species. In the present study, we investigated the persistence of propiconazole in peach roots following fall infusions and its potential for Armillaria root rot control in a commercial peach orchard. Four 12-year-old trees were infused with either 2 liters of a propiconazole solution at 0.4 mg ml -1 or water in September 2007. Bark tissue collected from primary roots of propiconazole-infused trees 48 hr and 6 and 12 months after infusion and analyzed using gas chromatography-mass spectroscopy contained 6.4, 1.4, and 0.9 µg propiconazole per gram fresh bark, respectively. Asymptomatic trees adjacent to trees that had died from Armillaria root rot (protective treatment) and symptomatic but alive trees (curative treatment) were infused with 1 liter of a propiconazole solution (0.4 mg ml -1 ) in spring and fall of 2008 and 2009 at a commercial peach orchard planted in 2005. Trees were rated for Armillaria root rot severity 6, 12, 24, and 36 months post-infusion. In the protective treatment, the survival rate in both non-infused and infused trees was 80% 36 months post-infusion. However, more (60%) of the propiconazole-infused trees remained asymptomatic compared to the control trees (30%). A significant difference was observed between the non-infused and propiconazole-infused trees following curative treatment. None of the control trees were alive after 36 months compared to 40% of propiconazole-infused trees. 438A. Amiri and G. Schnabel We conclude that fall infusion of peripheral trees of infection centers with propiconazole can slow the expansion of Armillaria root rot infection centers in commercial peach orchards.