Contexte

Alternariosis in apple trees, caused by the fungus Alternaria spp., is an emerging disease that was first reported in Girona in 2013. This disease causes leaf necrosis, which can lead to the premature defoliation of trees, but its most critical effect is its impact on the fruit, where small but highly visible necrotic lesions appear, reducing its quality and making it more difficult to market. This damage can lead to losses of between 10 and 40% of production, depending on the year and the property affected. The disease spread and affected around 20% of commercial apple farms in the province of Girona in 2017, and was particularly prevalent in the varieties in the Gala and Golden groups. However, treatments with fungicides specifically designed to control this disease have proven effective, and the figures show that the number of farms affected fell below 10% in 2018. This decline was also due to a 20 to 30% increase in the total number of treatments. This increase is significant, particularly given that these treatments are applied on a concentrated basis very near the harvest, and therefore have a direct effect on waste in the fruit. Given this situation, measures to reduce the number of treatments are required, either by optimising treatments when necessary, or by reducing the pressure of the disease by managing the inoculum.