Cohen, R., Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Research Center, PO Box 6, Bet Dagan, 50250, Israel
Shtienberg, D., Department of Plant Pathology, Agricultural Research Organization, Volcani Center, PO Box 6, Bet Dagan, 50250, Israel
Edelstein, M., Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Research Center, PO Box 6, Bet Dagan, 50250, Israel

The effect of the detergent Zohar LQ-215 alone or combined with the fungicide fenarimol (Rubigan) on cucumber powdery mildew (caused by Sphaerotheca fuliginea) was examined under controlled environmental conditions and in the field. In laboratory tests conducted on leaf disks, the efficacy of fenarimol was 30 times greater than that of Zohar LQ-215 as indicated by the ED50 values of the compounds (0.012% and 0.356%, respectively). Zohar LQ-215 did not reduce spore germination or germ-tube elongation, but inhibited the later stages of the disease cycle (i.e., mycelial growth and sporulation). Although the detergent was degraded relatively quickly, its effect on the polycyclic development of the disease lasted for up to 24 days after spraying. Low disease severity (2.4% compared with 27% in the control) was maintained following three applications of the detergent at 5 days intervals. In a greenhouse trial, a mixture of Zohar LQ-215 and fenarimol at half rate did not improve disease suppression beyond the effect of fenarimol applied alone at half rate. However, the effects of the two compounds were additive when applied in the field as a mixture. © 1996 Kluwer Academic Publishers.