Study of phytophthora species causing damping-off on cucumber in Tehran province greenhouses and evaluation of the efficacy of some fungicides on control of the disease

Damping-off Cucumber disease due to Phytophthora species is one of the most important diseases of horticultural crops. Pathogen attacks the roots and crown during entire growth stages, causing wilting or death of the plants. In this study, sampling from cucumber and tomato plants with symptoms of damping-off, root and crown rot was done from greenhouses located in Varamin and Pakdasht in 1394 and 1395 and after washing up and surface disinfection were cultivated on semi-selective medium of Phytophthora (CMA + PARPH). 16 isolates of the genera of Phytophthora drechsleri and P. nicotianae were isolated from crown, root and stem tissues of cucumber and tomato and pathogenicity confirmed on the host plants. In the second stage of the experiments, the efficacy of fungicide of Downy-G (Ridomil + Mancozeb WP 72%) in comparison with reference fungicides including Rosalaxil (Ridomil-Mancozeb WP 72%) and Previcur-Energy (Propamocarb Hydrochloride + Fosetyl Aluminium SL 840) in controlling cucumber damping-off based on a series of tests was investigated under greenhouse conditions (with two application method including soil incorporation system and soil drench system) and in the field conditions as soil drench system . Greenhouse trials with 6 treatments and 4 replications and field trials with 4 treatments and 4 replications were implemented at 2 locations in micro plots in Complete Randomized Design Block. The treatment evaluation carried out with determination of the percentage of infected plants in the period from emergence to 4-leaves stage. Greenhouse experiment results showed that Downy-G and Rosalaxil at 200 g/m3 of soil rates by 76.07% and 71.61% of decreasing disease in Soil Incorporation  application method, respectively, compared to infected control had the same effects in cucumber Damping-off disease control. In Soil Drench System application method, Previcur-Energy at 0.3% rates decreased disease by 99.64% compared to infected control and had the highest effects in disease control. In this application method, Downy-G and Rosalaxil at 0.2% rate decreased disease by 91.37% and 81.66% compared to infected control, respectively. The field trials results showed that Downy-G at 0.2% , Previcur-Energy at 0.3% and Rosalaxil at 0.2% rates decreased disease by 86.23% , 81.88% and 78.26%, respectively compared to infected control.