Management alternatives for strawberries diseases

Abstract

Powdery mildew of strawberry is caused by the obligate pathogenic fungus Sphaerotheca macularis f. sp. fragariae. The disease affects the leaves, flowers and fruit of this crop. Preharvest use of fungicide sprays may provide an alternative to the control of postharvest Mildew. However, fungicide resistance in Sphaerotheca spp. can result in the failure of disease control. In this study, the resistance of the strain of Sphaerotheca macularis isolated from strawberries was tested in vitro with three fungicides (Mancozeb, Fosetyl-aluminium and Propineb) enriched with Urtica dioica extract. The Mancozeb - U. dioica extract combination was very effective on seeding and sporulation, and moderately effective on growth. The Propineb - U. dioica extract combination was moderately effective on growth and sporulation but ineffective on seeding. Tests done with Fosetyl-Al alone were ineffective on seeding, growth and sporulation. The effects of different temperatures and relative humidity (RH), on germination and conidial germ tube length were evaluated on detached strawberry leaves. Our results suggest that alternating sprays using different classes of fungicides will be required to control mildew of strawberries, and that U. dioica extract may be an effective bio-fungicide incorporated into a fungicide spray program before the harvest for the fight against mildew of strawberries.