Epidemiology of powdery and downy mildew diseases on cucumber plants in Ghor El-Safi region [conidia, mycelium-isolation techniques; insolation; wind velocity]
1990
Al-Jaa'freh, J.Y.
Effect of environmental factors on powdery and downy mildews development as disease severity and incidence was studied on "Sahara" cucumber planted at two planting dates in the field and under plastic house conditions. Powdery and downy mildews diseases were isolated from most of the cucurbits and other hosts in the area. Sphaerotheca fuliginea was identified for the first time in Jordan as a causal agent of powdery mildew on cucumber plants in Ghor El-Safi. Identification depended on the asexual stage, because of the absence of perfect state. Source of inoculum of both diseases was isolated from the plant debris as a dormant conidia and mycelium or as a viable conidia on the alternative hosts as volunteer plants or ornamentals. Environmental factors were correlated with the disease development during the growing season, where the favorable T for powdery mildew was 22-27 deg C with high range of RH, and 16-19 deg C with wide RH (67-77%) for downy mildew. Daily total sunshine of 7-9 hrs decreased the severity and incidence of downy mildew while these of powdery mildew were increased. Downy mildew was favored with cloudy weather and 4.3 hrs total daily sunshine. There was no effect due to planting date on downy mildew development, compared with the greater effect on powdery mildew under plastic house conditions, while there was no effect of planting date on powdery mildew development in the field. Also there was no effect of fungicide application on powdery mildew development, but it has a significant effect on downy mildew development under plastic house conditions. Highest yield and fruit number were obtained from early planted plots which produced more than late planted plots
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