A strategy for controlling Cercospora leaf spot, caused by Cercospora beticola, by combining induced host resistance and chemical pathogen control and its implications for sugar beet yield

• Published in: Canadian journal of plant pathology Vol. 44; no. 4; pp. 518 - 533
• Main Authors: Morsy, Saad Z., Shady, Mohamed F., Gouda, Moustafa I., Kamereldawla, Bahnasy A., Abdelrazek, Mohamed A. S.
• Format: Journal Article
• Language: English
• Published: Philadelphia Taylor & Francis 04.07.2022; Taylor & Francis Ltd
• Subjects: acide salicylique; aqueous extract of Artemisia cina; Azoxystrobin; Benzimidazoles; Beta vulgaris L; Carbendazim; Cercospora; Cercospora beticola; Cercospora beticola Sacc; Crop yield; Demethylation; Disease resistance; Epoxiconazole; Extrait aqueux d'Artémisia cina; Field tests; fongicide systémique; Fungicides; Inhibitors; Leafspot; Pathogens; Pesticides; Propiconazole; Quinones; Salicylic acid; Sucrose; Sugar beets; systemic fungicide; Toxicity; Egypt
• ISSN: 0706-0661; 1715-2992
• DOI: 10.1080/07060661.2021.2024262

Cercospora beticola populations resistant to methyl benzimidazole carbamate (MBC), quinone outside inhibitor (QoI), and demethylation inhibitor (DMI) fungicides have been reported in Egypt. This pathogen causes a difficult to control variant of Cercospora leaf spot (CLS) on sugar beet. We conducted field experiments over two years to investigate treatment efficacies on MBC- and QoI-resistant, but partially DMI-sensitive, C. beticola from a research farm in Sakha, Egypt. DMI fungicides showed moderate efficacy with half the maximal effective concentration (EC 50 ). Efficacy was 67.2-69.1% and 63.4-63.6% for epoxiconazole (EPO) and propiconazole (PRO), respectively. When each fungicide was mixed with salicylic acid (SA) at EC 50 (EPO + SA) and EC 50 (PRO +SA), efficacy was 77.5-79.1% and 77.0-78.2%, respectively. The QoI fungicide, azoxystrobin, showed lower efficacy (46.4-49.5%) when applied alone, but enhanced efficacy when combined with SA at EC 50 /EC 50 (77.0-78.2%). Carbendazim alone was only 47.5-45.1% effective, but when mixed with SA, had a 67.1% co-toxicity factor in vitro, indicating antagonism between components. An Artemisia cina aqueous extract (WEA) combined with SA (WEA/SA) showed 76.0-78.2% efficacy, compared with 69.0-71.0% and 49.0-52.7% for WEA and SA, respectively. Single treatments were classified into five sensitivity classes from sensitive (<1) to resistant (>100) based on their EC 50 values. Significant increases in insensitivity were observed from 2015/16 to 2017/18. All treatments increased total yield, sucrose percentage, and recoverable white sugar compared with the untreated control. A combination of control strategies could allow for effective disease and fungicide resistance management.