Apples and pears grown under a narrow plastic roof or a plastic awning are less likely to be infected by scab and fruit rots. In fact, the results are so convincing that a profitable production of unsprayed fruit, at an acceptable price, is within reach.
Cultivation of apples and pears under roof or awnings has been a topic in the research conducted at the Department of Food Science, University of Aarhus for the last five years.
Throughout the years, the results obtained regarding diseases like apple scab have been uniform and highly significant. Apple scab is the major disease of apples and numerous fungicide sprays are applied to control the disease in both conventional and organic production.
The season for scab is long; it begins in early spring where raindrops cause scab spores to be ejected from old leaves on the ground onto young and susceptible leaves on the tree.
If the leaves are wet for a sufficiently long period (depending on temperature) the spores will germinate and infect the leaf. Scab infested leaves are less photosynthetic active, and later they will constitute an infection source for other leaves and fruits. On the fruit, scab will form black spots which make the fruit unappealing and disfigured, causing the fruit to be unmarketable for human consumption.
The rain roof is successful in preventing drizzle rain from reaching the trees, but cannot prevent trees from getting wet during periods of heavy rain and wind. However, the leaves and fruits typically get wet for a shorter period and this reduces the risk of a successful scab infection. In spring we do see some infected leaves, but as fruits need longer periods of wetness to become infected the roof is successfully preventing fruit scab. Also rot diseases, which are spread in the orchard and are developed later during storage, are successfully inhibited. Indeed, we have yet to come across a fungal disease that is not controlled by the rain roof however mildew cannot be accounted for due to general low infestations.
The big challenge and obstacle for rain roofs is the durability of the system. The first rain roofs in our experiments were permanent structures with a plastic cover that rarely survived the winter. In the research project 'Protecfruit', we have turned to awnings on a wire system. The awning consists of woven plastic flaps sewn to a net, which enables the flaps to open during windy conditions. The awning is pulled out at the start of the season and reassembled over the top wire at the end of the season. This system is much more durable, but it is still unclear how long the plastic can hold, and that is crucial for profitability.
Overall, we expect an investment of 300,000 kr / ha for the system. Economic calculations show that it is a good investment if the lifespan is 7 years; this is an acceptable investment at a 5 year time frame, but if the durability of the awning is less than that, the feasibility is doubtful. Denmark is a windy place, and an early autumn storm last year damaged the awnings, so at present the recommendation is to start on a small scale and gain experience under local micro and macro climate conditions.
ProtecFruit was supported financially by the Green Development and Demonstration Program (GUDP project) as part of the Organic RDD-2 programme, coordinated by the International Centre for Research in Organic Food Systems (ICROFS).