Abstract
In organic apple growing in South Tyrol, yield control is commonly achieved by removing buds and flowers with mechanical thinning machines and/or lime sulphur sprays. Netting structures have been tested in several trials for codling moth control, and promising results were obtained not only for codling moth control, but also for crop regulation (thinning). The trials conducted in 2010 and 2011, aimed at investigating the influence of different timings of net deployment (before bloom and during bloom, respectively) on thinning. Furthermore, also any possible negative side effect of the net was recorded. In both study years, a clear thinning effect of the netting structure emerged both before and after June fruit drop, resulting in increased fruit weight at harvest. Net deployment before bloom resulted in a significantly higher thinning effect than that during bloom, but in the plots netted before bloom also an increased number and severity of deformed fruits was recorded. Introduction Yield control is an essential practice in apple growing to obtain consistent and high-quality production. In integrated farming systems, growers rely primarily on synthetic plant growth regulators. These products are not allowed in organic farming. Thinning is done at flowering using mechanical thinning machines (Strimmer et al., 1997; Kelderer et al., 2009; Weibel & Walther, 2003) and/or applying lime sulphur sprays (Kelderer et al., 2006). The codling moth (Cydia pomonella) is one of the major pests on apple. Previous trials with netting structures (Romet et al., 2010; Kelderer et al., 2010) showed that netting trees can be a valuable tool for controlling this pest. As a side effect, fruit thinning has been recorded. We therefore decided to investigate the effect of netting structures, primarily designed for the control of codling moth, on fruit set reduction by deploying (closing) the nets already at flowering. In particular, two different timings of net deployment, respectively before bloom and during bloom, were investigated. The thinning effect before and after June fruit drop, yield, fruit weight, and fruit deformation index were recorded.