Comparative In Vitro Antifungal Activity of Azoxystrobin–Difenoconazole and Essential Oils Against Passalora fulva, the Causal Agent of Tomato Leaf Mold

Tomato leaf mold, caused by Passalora fulva, is one of the most destructive fungal diseases affecting greenhouse tomato production and can cause substantial yield losses under conditions of high relative humidity and moderate temperatures that favor pathogen infection and disease development. This study evaluated the in vitro antifungal activity of a commercial fungicide formulation, Priori Top® (azoxystrobin + difenoconazole), and three essential oils derived from Eucalyptus globulus, Artemisia herba-alba, and Mentha pulegium against two monoconidial isolates of P. fulva. Unlike previous studies, which have mainly focused on mycelial growth, the present work simultaneously evaluated the effects of the tested products on mycelial growth, sporulation, and conidial germination, providing a comprehensive assessment of antifungal efficacy across three key developmental stages of the pathogen. Antifungal activity was quantified by estimating IC50 and IC90 values using Probit regression analysis. The azoxystrobin–difenoconazole formulation consistently exhibited the highest antifungal activity across all evaluated parameters and showed the lowest estimated IC50 and IC90 values for both fungal isolates. Among the tested essential oils, Artemisia herba-alba exhibited the greatest antifungal activity, reducing mycelial growth by 83% and 78% at 500 ppm for isolates 1 and 2, respectively, and consistently outperforming Mentha pulegium and Eucalyptus globulus. Differences in sensitivity were observed between the two fungal isolates, indicating intraspecific variability in their response to the tested treatments. These findings demonstrate the strong antifungal efficacy of the azoxystrobin–difenoconazole formulation against P. fulva and identify A. herba-alba essential oil as the most promising botanical treatment for integrated management of tomato leaf mold. Further greenhouse and field studies are required to validate these findings, optimize formulation strategies, and evaluate the practical application of A. herba-alba essential oil under commercial production conditions.