Efficacy of Infinito and Bordeaux mixture in control of Peronospora destructor the causal agent of onion downy mildew

Downy mildew caused by Perenospora destructor is one of the most important onion diseases. In this research, the efficiency of Poltiglia Bordolese (Bordeaux Mixture WG 20%) at the rate of three, four and five kg/ha and Infinito SC 687.5 (flopicolide + probamocarp) at the rate of two L/h used to control downy mildew of onion disease and compared with control. The experiment was conducted in a randomized complete block design with six treatments in four replications in Jiroft and Behbahan, Iran. The results indicated that, in terms of effect on reducing the severity of the disease, Poltiglia showed a significant difference in compare with control. The comparison of effectiveness of treatments showed that it was related to those of poltiglia five kg/ha which was 63.5 %. In case of Infinito fungicide which used in Behbahan and Jiroft regions, it was 61.97% and 53.22 %, respectively. The comparison of the area under the disease progress curve (AUDPC) showed that in the control treatment with water spraying, this index recorded 21.4 and 20.1 unites per day in Behbahan and Jiroft respectively, and in the control treatment without water; this index was 20.4 and 16.9 per day, respectively. It indicates the role of free moisture in increasing the severity of the disease. The AUDPC index in Behbahan and Jiroft was 9.6 and 10 respectively, and belonged to the treatment of 5 kg/ha of Poltiglia fungicide. The Poltiglia fungicide at the rate of four Kg/h is recommended for controlling onion downy mildew disease.