Abstract

Some essential oils were evaluated as biocontrol agents against powdery mildew on Zinnia elegans, L. A field
experiment 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 zein
75% and distilled water as a control. Disease incidence and severity as well as other vegetative parameters such
as plant height, number of branches per plant, leaf area, fresh and dry weights of shoots, root length and fresh
and dry weights of roots were determined in the two seasons. Also, peroxidase and polyphenol oxidase activities
were 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 growth
and 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 of
peroxidase (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 alternative
method to fungicides for controlling powdery mildew of Zinnia plants.

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