Fruit growing: fertilization, fruit quality, crop protection, hedgerows, biodiversity

A survey has been carried out in two experimental organic orchards located at the INRA experimental station of Gotheron near Valence (Southeastern France). The program also associated the GRAB (Groupe de Recherche en Agriculture Biologique, Avignon). The aims were:(i) to acquire references about peach and apple organic farming; (ii) to improve the management of organic orchards by integrating some results of previous research; and (iii) to measure on the long term the effect of organic farming on the soil and on the arthropod community of the orchard. Soils were shallow and washed out stone soils presenting low pH, low organic matter content and low CEC (Cationic Exchange Capacity). Both orchards had been organically managed since planting, realised in 1994 for the apple orchard (Smoothee 2832 T(r) cultivar), and in 1999 for the peach orchard (Bénédicte(r) cultivar). Several parameters measuring the growth of the trees, the yield and the fruit quality were monitored. The low ability of the soil to store and supply nutrients to fulfill the tree requirements implied: (i) to use appropriate types of fertilizers, such as compost in autumn, with additional organic fertilizers which quickly mineralized in spring; (ii) to decrease the dose of fertilizers increasing therefore the number of doses; and (iii) to make additional sprays with oligoelements (Mn, B) in apple orchard. This strategy allowed to increase the pH, to improve the organic matter soil content and to preserve or to increase the availability of the soil nutrients. PEACH ORCHARD The yield was balanced at about 20 tons per ha with a high fruit quality (high sugar content, well balanced sugar/acidity ratio), that was favoured by a water supply restriction during the fruit first growth stages. Most probably because of a well-balanced nutrition and because of a non-disruptive pest management, aphids did not cause any damages: the green peach aphid (Myzus persicae) was very seldom monitored and Brachycaudus persicae did not affect seriously the trees. Most of all other pests were under control, using mating disruption against the oriental moth (Cydia molesta), sulphur against powdery mildew and mineral oils in winter against wintering arthropods. The main worrying pest was leaf curl due to Taphrina deformans. With a susceptible period lasting 6 to 7 weeks in winter, and a control of this desease relying on the use of copper, the total amount of this compound sprayed in one year can be high, unless the cultivar is not highly susceptible. APPLE ORCHARD The yield has increased regularly since planting until 2000. In 2001, the decrease in yield was most probably related to aphid infestation in 2000, which is lileky to have induced biennal bearing. The most prevailing pest was the apple rosy aphid (Dysaphis plantaginea) which proved to be very difficult to control and could damage seriously trees and fruits. Granulosis virus was sprayed against codling moth (Cydia pomonella), which allowed to control the level of wintering populations even if damages at harvest were sometimes high (from 4% to 14% total fruit damage at harvest during the 1995-2002 period). Apple scab (Venturia inaequalis) was satisfyingly controlled with copper before blooming and then with sulphur (less than 1% fruit damage at harvest), but the number of sprays, in spite of the break of the protection after the end of the primary contamination, remained high (from 10 to 15 treatments per year). Apple scab resistant cultivars are undoubtly worth to optimize organic apple farming. The populations of secondary pests did not increase along the survey. This survey allowed to point out critical points in fruit organic farming, above all in pest management, and to propose further experiments to perfect strategies to be used in organic orchards. Effect of organic farming on soil and arthropod community was planned to be checked on the long term, during the 2002-2004 period