Efficacy of Some Essential Oils on Controlling Powdery Mildew on Zinnia (Zinnia Elegans, L.)

Some essential oils were evaluated as biocontrol agents against powdery mildew on Zinnia elegans, L. A fieldexperiment was carried out during the two successive seasons of 2006 and 2007 using marjoram, clove, cinnamon, garlic, ginger and fennel oils, added as foliar spray at 2 levels of 0.05 and 0.1 ppm besides Kema zein75% and distilled water as a control. Disease incidence and severity as well as other vegetative parameters suchas plant height, number of branches per plant, leaf area, fresh and dry weights of shoots, root length and freshand dry weights of roots were determined in the two seasons. Also, peroxidase and polyphenol oxidase activitieswere determined after 24 hour from the last spray in leaves samples. The highest significant decrease in disease incidence and severity and the best results for most studied growthand flowering parameters and total green colour were recorded with ginger, cinnamon and clove oils, respectively each at 0.1 ppm compared to the other treatments in both seasons. In addition, the activities ofperoxidase (POX) and polyphenol oxidase (PPO) enzymes were increased as a result of oils sprayed on plants. These findings provide for a rational basis of a possible utilization of these essential oils as a safe and alternativemethod to fungicides for controlling powdery mildew of Zinnia plants