Effectiveness of Low Copper-Containing Chemicals against Olive Leaf Spot Disease Caused by Venturia oleaginea

The high level of copper (Cu) accumulation in the soil, the risk of surface water contamina-tion, and the potential public health problems due to Cu entering the food chain have raised concerns on the use of Cu compounds in agriculture, including olive growing. As a consequence, there is worldwide regulatory pressure on agricultural systems to limit the use of Cu compounds. Hence, a field trial was carried out to evaluate the effectiveness of low copper containing chemicals to control olive leaf spot (OLS) disease caused by Venturia oleaginea. The trial was conducted in 2021 in an olive (cv. Nabali Baladi) grove in Palestine. Copper complexed with lignosulphonate and gluconate (Disper Cu Max® ) and the self-defense inducer Disper Broton GS® were evaluated and compared to dodine and the traditionally and frequently used copper hydroxide. In addition, untreated trees were used as the control. Treatments were made in March, July, and August. In March 2021, leaves grown in 2020 were present and 100% infected. V. oleaginea infections caused defoliation in untreated and treated olive trees with varying degrees of intensity: the Control had the most defoliation, followed by copper hydroxide and Disper Cu Max®, whereas dodine and, in particular, Disper Broton GS® had the least. All treatments reduced symptomatic leaves but their efficacy varied significantly: copper hydroxide was the least effective, Disper Cu Max® was intermediate, dodine and, mainly, Disper Broton GS® were the most effective. Overall, the results are promising since Disper Cu Max® and Disper Broton GS® were able to significantly reduce OLS damage and the amount of copper used for treatments.