Evaluacion del efecto de la “malla sanitaria” sobre el control de la sarna del manzano causada por Venturia inaequalis

Apple is the most important deciduous fruit crop in Uruguay. Apple scab caused by the fungus Venturia inaequalis is the main crop disease.   Its control is based on chemical aplications, and up to 12 applications can be made each season.  The main pest insects affecting this crop are carpocapsa (Cydia pomonella) and the native leafrollers, Argyrotaenia sphaleropa and Bonagota salubricola (Lepidoptera: Tortricidae).  Numerous sprays with insecticides are carried out to control them. Consumers are increasingly demanding in terms of the safety of the fruit, both chemical and microbiological. In order to respond to these demands, a regional insect control program has been implemented based on sexual confusion by pheromones, thus reducing the use of insecticides. Recently, and for the same purpose, the use of exclusion meshes as a pest control method in apple trees was introduced for the first time in Uruguay. As a secondary result of the use of the insect mesh system, an apparent reduction in the incidence and severity of Apple Scab has been observed. If this is verified, the anti-insect meshes would contribute to minimize fungicides sprays to control V. inaequalis. To evaluate whether the use of insect exclusion nets contribute to reduce the incidence and severity of apple scab, a field trial was carried out on a Red Delicious apple orchard. Treatments were absolute control without any application of fungicides, Alt´Carpo exclusion net in a single-row netting systems and control where scab was controlled by periodic applications of fungicides. Each treatment was applied to groups of three rows of 25 plants. After three periods of infection, the incidence and severity of scab in leaves and the incidence in fruits were evaluated. In order to determine if the reduction in the incidence and severity of scabies caused by sanitary nest is due to the fact that it prevents the arrival of V. inaequalis ascospores to susceptible tissues, the concentration of ascospores inside and outside the mesh was quantified using   Burkard volumetric spore traps. Results showed that the sanitary mesh significantly reduced the incidence and severity of scab on leaves and fruits. Under the mesh, the concentration of ascospores was significantly lower, which would explain the lower incidence of the disease. Reducing the incidence and severity of apple scab on trees covered by the mesh is not enough to eliminate fungicide applications directed at V. inaequalis control.