The high level of copper (Cu) accumulation in the soil, the risk of surface water contamination, 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.

The efficacy of using a synthetic (azoxystrobin + difenoconazole), copper-based (copper oxychloride) and low-content copper compound (copper complexed with gluconate and lignosulphonate) fungicides for controlling Venturia oleaginea, the causal agent of olive spot disease, was evaluated in an olive (cv. Nabali) orchard located in the Kafr Qud area (Palestine) in 2017–2018. Treatments were applied at three different times (February, April, and August). In January 2017, at the beginning of the experiment, about 90% of the leaves grown in 2016 were infected. Defoliation was determined by counting the leaves on the labeled branches initially and then periodically. It increased gradually in both the control and treated trees, but those treated with azoxystrobin + difenoconazole or with copper complexed with gluconate and lignosulphonate showed a slower defoliation rate. During 2017, new shoots grew and new leaves developed. All treatments reduced the drop of new leaves with respect to the control, with positive effects on the reproductive activity (inflorescence growth and yield). Overall, all treatments significantly reduced the disease, thus indicating the possibility of greatly reducing infections if treatments are regularly applied each year, also with traditional (copper-based) fungicides. Due to their capability of penetrating inside the vegetative tissue, azoxystrobin + difenoconazole or copper complexed with gluconate and lignosulphonate reduced/slowed down the drop of infected leaves. The use of these fungicides is therefore particularly recommended when olive leaf spot disease is severe. The use of low-content copper compounds allows the amount of metallic copper used for the treatments against V. oleaginea to be greatly reduced.