Orchard specific management of scab (Venturia inaequalis) on apple

Abstract: Scab, caused by Venturia inaequalis, is one of the major fungal diseases in Belgian fruit production, and over 50% of the pesticides used in apple cultivation are used for its control. As such, a good management of the primary infection moments caused by ascospores at the beginning of the season, is essential. An accurate warning system in the spring is, therefore, an ideal strategy. The current scab warning system of the Research Station of Fruit Cultivation (pcfruit vzw) is based on: (1) evaluation of ascospore releases from heavily infected scab leaves and (2) climatological infection risks. As such, the warning system is considered very valuable and allows fruit growers to control their applied treatments, products and dosages. However, the use of a worst case does not take the initial inoculum pressure of a specific orchard into account. Consequently, the warning system provides potentially biased information concerning the intensity of scab infections which leads to maximal treatment on each possible infection moment. Too many treatments (or at the wrong times) is cost and time expensive, and accelerates the occurrence of resistant species. We have developed a method to artificially induce ascospore releases followed by molecular assessment resulting in a good estimation of the initial scab at a specific orchard, prior to the season. Moreover, this technique is also being used to monitor the ascospore release during the season in individual orchards. Such information is critical to better advice fruit growers in their use of pesticides to control scab infections. This will result in a better, more orchard specific scab control strategy that might result in a reduction of treatments, which then affects the residues on apples and might lead to a significant decrease in costs for the fruit grower.