The effect of different leaf removal systems and fungicide combinations on phytophagous pests and predatory mite populations, and yield of organic Sultani Cekirdeksiz grape variety

Abstract: The effects of four different leaf removal (removal of 2 leaves at fruit set, removal of 4 leaves at veraison, removal of 6 leaves at fruit set and at beginning of ripening, untreated control) in combination with two different foliar applications (sulfur or sodium bicarbonate) against powdery mildew (Erysiphe necator Schwein.) have been investigated in terms of population densities of pests and predatory mites, and yield and quality of grape in organic and conventional plots between 2005 and 2007. The different levels of leaf removal generally had no significant effect on damage by European grapevine moth (Lobesia botrana Den. & Schiff.) and predatory mite populations. Only in 2005, lower infestation of L. botrana has occurred in the 2 leaf-removal treatment at fruit set. The highest populations of grape erineum mite (Colomerus vitis Pgst.) were counted when 6 leaves were removed at fruit set and at beginning of ripening in 2006. Although any statistical difference has not been determined among the treatments, population densities of the two-spotted spider mite (Tetranychus urticae Koch) in 2005 and 2006, and of grape leafhoppers (Empoasca spp.) in 2006 have been higher in sodium bicarbonate-applied plots than in those treated with sulfur. In Turkey, a registered plant protection product is unavailable against grape leafhoppers and two-spotted spider mites in organic agriculture. In some years, they can heavily attack the plants. Natural biological control needs longer time to suppress these pests. For this reason, it might be logical to recommend sulfur instead of sodium bicarbonate for the management of powdery mildew, the main disease. Predatory mites have generally been observed in the plots from late-July or early-August, when sulfur sprayings against powdery mildew are completed. It has been found that the removal of 6 leaves at fruit set and veraison has partly increased the yield and quality of Sultani Cekirdeksiz grapes in organic vineyards. It has been concluded that leaf removal at different phenological stages have not statistically effected fresh grape yield (kg/vine tree).