Comparison of the efficacy of low-copper content products and conventional copper fungicides in controlling olive leaf spot (Venturia oleaginea, Castagne)

This study compared sustainable, low-copper strategies with conventional fungicides for controlling olive leaf spot ( Venturia oleaginea ), focusing on defoliation, visual and latent incidence, and leaf anatomical responses. Alternative compounds, including copper gluconate, a low-copper content product, and a combination of a low-copper content product with diatomaceous earth, were tested against a Bordeaux mixture and copper oxychloride standard. All alternative treatments reduced defoliation compared to the untreated control. The synergy between the low-copper content product and diatomaceous earth resulted in the greatest leaf persistence (40%) and the lowest infection intensity on older leaves during spring. A significant negative correlation (r = -0.493) between palisade thickness and symptomatic intensity suggests these treatments may enhance structural resistance by thickening mesophyll layers. Furthermore, primary infections on new growth were recorded as early as July, triggered by summer dew moisture, indicating an epidemiological shift under changing climatic conditions. These findings demonstrate that low-copper content products, supplemented by biostimulants and physical barriers, provide protection equivalent to conventional standards while reducing copper accumulation, aligning Mediterranean olive production with EU strategic goals.