Direct control of sooty blotch in organic pome fruit production

Summary

The use of organic fungicides to reduce infestations of sooty blotch can be combined with standard crop protection. In addition, the use of these agents also has an effect against other diseases.
Practical recommendations
Introduction
• The pathogen agents change from region to region, and during the season, the most common agents are: Cladosporium sp., Alternaria sp., Schizothyrium sp., Aureobasidium sp., Phoma sp., Fusarium sp., Peltaster sp., Botrytis sp., Penicillium sp., Epicoccum sp., Gloeodes pomigena, Geastrumia sp., Stomiopeltis sp., etc.
• The pathogens responsible for sooty blotch overwinter in the orchard on branch tips, bark crevices, dead wood and mummified fruits.
• Young fruits can be infected by the fungi very early after flowering, but the first symptoms appear only during July.
Time of application and strategies
• Because the pathogens of sooty blotch disease can infect the apples throughout the growing season, repeated treatments are necessary during the growing season.
• Especially in orchards with increased infestation pressure and in years with wet weather conditions, early and regular treatments are essential to regulate the rain spot with biological preparations.
• For a sufficient effect, treatments must be started in June at the latest, before the first symptoms appear.
• Treatments against sooty blotch are often combined with applications against other diseases. Most products used in the primary season against scab have a positive side effect for controlling sooty blotch (see: Plant protection products).
Plant protection products
• Products based on potassium bicarbonate have good efficacy against sooty blotch. It has been shown that unformulated carbonates do not match the effectiveness of formulated products. Adding wettable sulfur can improve the effect of potassium bicarbonates.
• Preparations with copper or lime sulfur also have some effect.
• The sole application of wettable sulfur or acidified clay mineral preparations do not have a sufficient effect.
Treatments
• Until June: Potassium bicarbonate (4-5 kg/ha) and wettable sulphur1 (2-4 kg/ha), which are used to control apple scab, also have a good effect against sooty blotch.
• June to harvest: strategy can be continued against sooty blotch in humid phases, whereby the amount of sulphur1 must be adjusted to the temperatures.