Relationship between the Control Effect of Fungicides on Powdery Mildew (Sphaerotheca humuli) and Their Deposits on Strawberry Leaves

Abstract

The present study was undertaken to investigate the relationship between the quantity of fungicide deposits on strawberry leaves and the control effect on powdery mildew (Sphaerotheca humuli). When fungicide was sprayed over strawberries by swinging a nozzle pendulously as conventionally done, the fungicide deposits on the lower surfaces of leaves were insufficient to control the disease. On the other hand, when fungicide was sprayed in such a way as to cover the lower surfaces of leaves as well, the disease was controlled to a sufficient level. Our investigation of the quantity of fungicide deposits on leaves in relation to the leaf configuration disclosed that the conventional spray method was not adequate to deposit a sufficient quantity of fungicide on the lower surfaces of leaves, especially in the ‘Toyonoka’ variety, because the leaves are spreading in the ‘Toyonoka’ compared with the ‘Nyoho.’ The most effective application method to increase fungicide deposits was to spray fungicide not only over the plants and from the furrow but also from the middle of the ridge. © 1993, Pesticide Science Society of Japan. All rights reserved.