الفهرس 
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Abstract
Powdery mildew caused by Erysiphe heraclei DC is considered one of the most important foliar diseases that attack Coriander and Dill in the different cultivation areas, causing a great damages in the yield. The typical symptoms of powdery mildew were observed on plants during two successive growing seasons, 2013/2014 and 2014/2015 in several fields in Fayoum governorate. Based on the morphology of anamorph and teleomorph stages, the causal agent was identified as the fungus E. heraclei. The optimum temperature for E. heraclei conidial germination was definite as 25oC, the minimum was 5oC and the maximum was 30oC. Conidia were able to germinate within a wide range of relative humidity (10-100%) however, the highest germination was recorded at 70% R.H. (78.20%). Also, the highest germination was achieved 24 hours after incubation (86.50%). Host range of E. heraclei confirmed that, among the nine cultivated host plants belong to the family of Apiaceae, Coriander, Dill, Fennel, Parsley, Caraway, Visnaga and Carrot were susceptible to infection with powdery mildew. Coriander and Dill were more susceptible to infection with powdery mildew at 70 and 50 days old, respectively. In in vitro study, all tested treatments significantly reduced conidial germination. Complete inhibition was achieved by Tilt-25 fungicide followed by Topas-100 and Micronite-80. Among four commercial products of bioagents, Bio-Zeid gave superior inhibition to conidial germination (86.42%) followed by Clean-Root (81.55%), each at 2000 ppm. Also, Garlic extract the best inhibition (75.87%) followed by Blue gum extract (72.62%), each at 75 %. Among six essential oils, Clove oil followed by Peppermint and Marjoram oils, each at 2000 ppm achieved obvious significant reduction to the conidial germination. Relating to chemical inducers, Ascorbic acid was the most effective followed by Potassium silicate.