Screen house experiment was carried out at Sakha Agricultural Research Station, Kafr El-Sheikh Governorate during 2007/2008 season to study the relation between fungicide and plant extract application on Cercospora beticola incidence and related characters as well as invertase enzyme on sugar beet. Two cultivars of sugar beet were selected; the two cultivars; Ras Poly and Fareda were used and planted in a split plot design. Topsin M70 (1 gm/liter) and plant extract Khella "Ammi visnaga" or pick-tooth (4000 ppm) were sued to control the disease. Artificial inoculation was done by using conidiospores suspension of Cercopora beticola. Inoculation was done 90 days after planting. Chemicals were applied three days before inoculation. Different traits were measured like, disease severity (%), root weight/plant, sugar percentage, sugar loss to molasses %, invertase enzyme activity, impurities in leaves and roots (Na + , K + and -amino-N), TSS %, chlorophyll content of leaves, purity (%), loss % for root and sugar. Seven readings to asses the disease incidence were taken. Disease severity (%) of cercospora leaf spot disease incidence was increased gradually especially for Ras Poly cv. than Fareda cv. under infected condition, but showed less values when treated with Topsin M70 followed by Khella. On the other hand, root weight, TSS%, sugar percentage, purity were highly affected than those under fungicide and plant extract treatments and loss percentages for root and sugar reached to maximum for Ras Poly than Fareda cv. Enzymatic activity of invertase reached the maximum under inoculation, while it was less when treated by Topsin M 70 and Khella plant extract. Na + and amino N increased by increasing disease severity (%), while K + behaved in different manner. Concerning reducing sugars in roots, recoverable sugar (%) and sugar loss to molasses increased by increasing disease severity (%), low values were obtained under fungicidal and plant extract treatment. Plant extract and resistant cvs, must be recommended to reduce the pollution either in water or in the soil of sugar beet plantations.

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