Benefits and limitations of apple production under rainproof covers

To reduce the use of fungicides against apple scab and storage diseases, rainproof covers placed on the top of apple orchards have been experimented by eight European research institutes in France, The Netherland, Spain, Italy, Switzerland and Germany. The efficacy of rainproof covers against apple scab (Venturia inaequalis) depends on susceptibility of the apple cultivars and the scab pressure in the orchard. It appeared that apple scab reduction is more variable on shoots (from 25 to 100% reduction) than on fruits (between 85 and 100% reduction). Regarding fruit rot diseases, such as lenticel rots, the number of affected fruits is significantly reduced (on average 67%). However, other diseases such as powdery mildew (Podosphaera leucotricha) and pests such as woolly apple aphid (Eriosoma lanigerum) are favoured by the microclimate under covers. The two main constraints encountered are the life span of the rain covers (weather resistance, less luminosity) and, for certain apple cultivars: yield losses and reduction of fruit quality (i.e., less colouring). The technical challenges consist in adapting irrigation under the rain covers and managing rainwater on the inter-row. To improve and optimize the systems, new studies are started on manual or automatic mobile systems to open and close the covers depending on the rainfall.