evaluation of some fungicides for the control of armillaria root rot of walnut trees

Armillaria root rot, primarily caused by the closely related species armillaria mellea, is a prevalent disease affecting walnut trees globally, leading to stunted growth and plant mortality. currently, no walnut rootstock genotypes have been identified that offer complete resistance to this disease. the application of chemical fungicides represents the most straightforward and accessible method to mitigate the damage caused by armillaria root rot in walnut trees. this research aimed to assess the prevalence of armillaria root rot in both traditional and commercial walnut orchards and to evaluate the efficacy of chemical fungicides, specifically thiophanate-methyl and triazole compounds (propiconazole, cyproconazole, and hexaconazole), in reducing the severity and incidence of root rot. samples collected from various commercial and traditional orchards in iran were analyzed for the presence of the causal agent of the disease. using a combination of morphological and molecular techniques, five isolates of a. mellea were identified. results indicated variability in pathogenicity among the a. mellea isolates, ranging from pathogenic to weakly pathogenic. moreover, the fungicides tested were effective in completely inhibiting mycelial growth at the minimum inhibitory concentration (mic). however, the effectiveness of each fungicide in reducing disease incidence varied. notably, thiophanate-methyl significantly outperformed the triazole fungicides in inhibiting disease progression. the findings suggest that thiophanate-methyl, when applied at the minimum fungicidal concentration (mfc) upon the initial appearance of disease symptoms, holds promise for the management of armillaria crown and root rot in walnut orchards.