Suppression of powdery mildew (Sphaerotheca fuliginea) in cucumber by the detergent Zohar LQ-215

Abstract

The effect of the detergent Zohar LQ-215 alone or combined with the fungicide fenarimol (Rubigan) on cucumber powdery mildew (caused bySphaerotheca 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.