Efficiency of Some Biocides as Safe Alternatives to Fungicides on Cercospora Leaf Spot Control, their Effect on Biochemical Constituent and Yield of Sugar Beet

Cercospora leaf spot incited by Cercospora beticola Sacc. is a very detrimental fungal disease affecting sugar beet crop production in Egypt as well as sugar yield. The efficacy of four selected commercial biocides i.e., Biobac, Bio-Arc, Bio-Zeid and Plant Guard, was investigated to control Cercospora leaf spot on sugar beet plants in comparison with the recommended fungicide Score as a check difenoconazole fungicide as well as untreated control under field conditions at Sakha Agricultural Research Station, Kafr El-Sheikh Governorate, Egypt. The biocides and fungicide were sprayed at different three spray regimes as two sprays, four sprays or six sprays with 15 days intervals between sprays for such treatment. All tested biocides and Score fungicide led to significant decrease in Cercospora leaf spot disease severity of the treated sugar beet plants in comparison with control treatment. Increasing spraying numbers of the tested biocides or Score fungicide from two times to six sprays per season caused increasing reduction of Cercospora leaf spot severity. Spraying Plant guard, Bio-Zeid and Biobac biocides six times achieved very comparable effectiveness to Score treatment at the same spray regime in the two growing seasons 2015/2016 and 2016/2017, whereas, Bio-Arc was the less effective biocide treatment particularly when sprayed two times per season. All tested biocides at different spraying regimes led to significant increase in values of phenolic compounds, total chlorophyll, (achieved higher quality traits at the end of the season), sucrose (%) and purity (%) and top, root as well as sugar yield quality of sugar beet were significantly increased. The impurities of produced sugar as sodium, potassium and α-amino nitrogen in the juice were significantly decreased in comparison with untreated control during the two growing seasons. Overall results clarified that spraying Score fungicide or Bio- Zeid, Plant guard and Biobac, respectively six times resulted the highest increase of quality traits as sucrose (%) and purity %) and top, root and sugar yields of sugar beet and significant decrease in total amino acid, juice impurities (Na, K and α-a N %), whereas Bio- Arc when applied two times recorded the least effective treatment close to the control during the two growing seasons 2015/2016 and 2016/2017. It was concluded that biocides, Bio-Zeid, Plant guard and Biobac could be sprayed six times/season at 15 days intervals as alternatives to fungicide applications to control Cercospora leaf spot of sugar beet and to produce higher yields of root and sugar with better quality.