No- or Low-Content Copper Compounds for Controlling Venturia oleaginea, the Causal Agent of Olive Leaf Spot Disease.

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.

Dodine an effective alternative to copper for controlling Venturia oleaginea, the causal agent of pea-cock eye disease, in highly infected olive trees.

A trial was carried out in central Italy in an olive orchard of cultivar Moraiolo, highly infected by Venturia oleaginea. The aim of the investigation was to evaluate the effects of autumn and spring applications of copper oxychloride or dodine to control the disease. Non treated trees were used as the control. The effects of the fungal attacks on leaves and inflorescence development confirmed the high susceptibility of the cultivar Moraiolo to the disease. The results show that in trees heavily infected, but with most of the infected leaves at the early stage of the disease (asymptomatic phase), treatments with dodine had a curative effect, with consequent reduction in the appearance of symptomatic leaves and defoliation with respect to the control or copper-treated trees. The use of dodine against the autumnal attacks of V. oleaginea allowed most of the old leaves to be maintained until the new ones had formed, which is important for the growth processes during the early part of the growing season. Overall, the results indicate that to efficiently control the pathogen using copper compounds, treatments must start soon after the beginning of the attack and be repeated in order to maintain the infection at a low level. Dodine can be efficiently used if there is a great increase in infected leaves. The use of dodine to solve particular situations and not for normal repeated use is regulated by the fact that in some countries, Italy included, protocols for integrated pest management allow only one dodine treatment/year.

Olive leaf spot caused by Venturia oleaginea: An updated review.

Olive leaf spot (OLS) caused by Venturia oleaginea is widespread in all olive-growing areas and continents, where can cause severe yield losses. The disease is often underestimated for the difficulty to reveal early leaf symptoms and for the pathogen-induced phylloptosis, which creates the illusion of healthy and restored plants. The present review provide updated information on taxonomy, pathogen life style and cycle, epidemiology, diagnosis, and control. Application of copper-based fungicides is the main method to control OLS. However, the regulation 2009/1107 of the European Commission include these fungicides in the list of substances candidates for substitution. It is therefore urgent to find alternative control strategies especially for organic agriculture. Among new approaches/strategies for controlling OLS, promising results have been obtained using nanotechnology, endophytic microbes, and biostimulants.