Although consumer demand for approved organic apples is increasing throughout Europe, production is limited by disease control difficulties. Apple scab, caused by Venturia inaequalis (Cooke) G. Wint., is a major disease of apple trees. It results in important economic losses, especially in the rainy agricultural areas of the world, where control is necessary for commercial apple production. Yield losses in Belgium caused by apple scab would be about 70% if no control measures were taken; thus, 15 to 25 conventional spray applications per season are used to prevent apple yield loss under Belgium’s weather conditions. In organic production systems, the use of synthetic fungicides is not allowed and scab is controlled mainly by using copper and sulphur fungicides. Copper has a poor ecotoxicological profile and there are new European copper restrictions. For this reason, alternatives to copper fungicides have to be found. With the very limited number of fungicides available in organic production, apple scab control is often difficult. This is exacerbated by the use of commercial apple cultivars that are very susceptible to diseases.
Objectives
The aim of this study is to develop a successful strategy for the control of apple scab using environmentally friendly substances compatible with organic production systems. Growers need scientific knowledge about profitable organic fruit production in Belgium via the global management of the ‘orchard’ ecosystem. The use of chemical products is still necessary for professional growers, but we need to improve the effectiveness of these products and choose the optimal combinations of factors and techniques in order to reduce input rates. Various techniques can be applied, including: Choosing adapted varieties with both a low susceptibility to the major diseases and good commercial potential; Creating an ecological environment attractive to natural enemies; Using warning systems based on accurate software to determine infection risk periods; Maintaining a low infection potential; Using efficient mechanical measures for weed control; Using organic manures and good soil management to encourage improved biological activity; Managing the trees to supply a suitable balance both for growth and fruit production, based on the SOLAXE concept developed by the ‘MAFCOT’ group.
Description of tasks
The experiment started in 2002 and has been conducted in a well-maintained experimental apple orchard in Gembloux. A split-plot design was adopted, with six randomized blocks. Each block is composed of six rows (plots) of 24 dwarf trees, grafted onto M9 rootstocks. The blocks have four partially scab-resistant cultivars (Rubinstep-Pirouette, Reinette des Capucins, Reinette de Waleffe, Reinette des Capucins and Pinova) and four Vf scab-resistant cultivars (Topaz, Zvatava, Initial and JN 20/33/58). Each of the 10 experimental spray schemes covers a minimum of 144 trees. The spraying is carried out using a specific experimental prototype of a Munckhof tunnel sprayer. In order to limit copper use, various spray schemes are tested each year, including sulphur formulations, calcium polysulphur and potassium bicarbonates. Potential infection periods, based on the Mills criteria, are recorded in the field with a METY computer-based weather recorder coupling with a scab warning system. For assessing apple scab severity on trees, a standard 9-point scale was used. Fruits from the whole harvest were classified according to their symptoms in October. As part of this project we are also studying the use of natural products as a source of Systemic Induced Resistance (RSI or SAR). By using Vf resistant cultivars, we are aiming to test strategies for enhancing the durability of scab Vf gene protection in order to prevent its breakdown by virulent races. The strategy consists of applying protective or ‘stop-spray’ substances when there are high primary infection risks. With polygenic resistance cultivars, various strategies will be applied in order to reach optimal apple scab control. For studying the environmental impact of the various spray schemes, we are using several agro-environmental indicators. As part of the active substances screening procedure, comparative effectiveness tests against scab were carried out on seedlings under controlled conditions. The effects of temperature and density on substance effectiveness were studied. Similarly, studies are being carried out to define the optimal application doses of protective substances depending on the scab susceptibility ranges of the various partially resistant cultivars. In vitro screening was carried out to study the comparative effect on pathogen growth of new mineral substances used as fungicides.
Expected results
The aim of this 8-year organic farming project is to define effective strategies for controlling scab and other diseases in organic farming systems that can also be used where IPM approaches are being implemented. It will provide scientific information on reducing the use of pesticides, including fungicides and, in particular, copper products. The main goal of the project is to promote the development of adapted production tools that are economically viable for growers. As environmental considerations become more important in crop protection, new technologies must be developed, and this study seeks to address this need in the context of the requirements of growers and consumers.
