Apple scab (Venturia inaequalis) and pests in organic orchards

Domestication of apples goes back several thousand years in time and archaeological findings of dried apples from Östergötland in Sweden have been dated to ca 2 500 B.C. Worldwide, apples are considered an attractive and healthy fruit to eat. Organic production of apples is increasing abroad but is still at very low levels in Sweden. This study deals with major disease and pest problems in organic growing of apples. It concentrates on the most severe disease, the apple scab (Venturia inaequalis). Resistance to apple scab was evaluated during three years in over 450 old and new apple cultivars at Alnarp and Balsgård in southern Sweden. There were significant differences between the cultivars and years. About ten per cent of the cultivars had a high level of resistance against apple scab. The correlation between foliar and fruit scab was stronger when the scab infection pressure was high (1998-1999), compared to when it was low (2000). Polygenic resistance is a desirable trait since such resistance is more difficult to overcome by the pathogen. A common denominator for polygenic resistance among the cultivars assessed was 'Worcester Pearmain'. The leaf infection of apple scab was compared at three locations: Alnarp, Kivik and Rånna (Skövde) in an observation trial for 22 new apple cultivars. The ranking of the cultivars was similar at the three locations. The best cultivars, 'McShay' and 'Sansa', are unfortunately not suitable for growing in Sweden, due to climatic conditions. However, several other cultivars might be useful in organic growing. The incidence of apple scab races was investigated for the first time in Sweden. Races 1-4 and 6 were reported from different geographical locations in Sweden (1999-2001), and tested in growth chamber/greenhouse trials. Race 1 was present at all sites and race 7 was reported on Malus floribunda 821 for the first time in a field trial at Kivik in 2002. Apple scab lesions were also found on the ornamental species Malus baccata jackii. In an experimental organic orchard with 'Amorosa' and 'Discovery' interplanted with ornamental shrubs, the insect and spider fauna was investigated. Codling moth was considered to be a key pest in the orchard. Winter moth and apple sawfly damaged the fruit to a significantly higher extent in 'Discovery' than 'Amorosa'.

Author

• Boel Sandskär

• malus
• apples
• venturia inaequalis
• scabs
• orchards
• organic gardening
• fruit crops
• disease resistance
• mixed cropping
• beneficial organisms
• sweden
• Apple cultivars
• apple scab races
• resistance biology
• rosy apple aphid
• sanitation practices
• interplanting

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https://pub.epsilon.slu.se/162/

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oai:pub.epsilon.slu.se:162