Abstract
Within the Core Organic 2 Project Bio-Incrop, composts based on different organic matter were tested for their activity against apple replant disease. The trials were conducted during 2013 and 2014 in a greenhouse on potted M9-rootstock plantlets, which is the most commonly used rootstock in organic and integrated apple orchards in Europe. To prove the presence of apple replant disease, potted M9-rootstock plantlets were grown on sterilized soil and compared to plantlets grown on unsterilized soil (preliminary trial). The same unsterilized soil was then used in the trials in order to compare the efficacy of different composts against apple replant disease. The application rates of the composts tested in 2013 resulted to be too high. The high salt content of several composts negatively affected root growth, as shown by the numerous plantlets that died soon after emergence of shoot primordial. In 2014, the application rates of the tested composts were therefore considerably reduced. Nevertheless, also in 2014 no significant or at least numerically relevant increase in shoot length and shoot dry weight was recorded for plantlets grown on compost-treated soil in comparison to plantlets grown on unsterilized, untreated soil.