Balancing nitrogen and fungicide applications to minimise carrot leaf blights

• Published in: Phytopathology 2008-06, Vol.98 (6), p.S101-S101
• Main Authors: Mcdonald, M, Westerveld, S M, Saude, C
• Format: Article
• Language: English
• Subjects: Alternaria; Cercospora; Daucus
• ISSN: 0031-949X

Alternaria leaf blight (A. dauci (Kuehn) Groves and Skolko) and Cercospora leaf spot (C. carotae (Pass.) Solheim) are managed together with an extensive fungicide spray program, but there is the potential to reduce fungicide applications through nitrogen (N) application. Every combination of three rates of N (0, 110 and 220 kg/ha) and three fungicide treatments (0, 3 and 5 sprays) were applied to carrots grown on mineral soil in Ontario, Canada in 2006 and 2007. The severity of both diseases was assessed biweekly throughout the season and at harvest. Total and marketable yield were assessed at harvest. The area under the disease progress curve for both diseases decreased with increasing number of fungicide sprays in 2006, but was unaffected by N application. In 2007, the area under the disease progress curve for each disease was lowest when carrots received 220 kg/ha N and three or five fungicide sprays, and highest when carrots received no N and no fungicides. Carrots treated with the high rate of N and no fungicides had the same level of Alternaria leaf blight as carrots treated with no N and three or five fungicide sprays. Disease severity at harvest decreased with increasing number of fungicide sprays and decreased slightly with increasing N application in both years. Total and marketable yield increased with increasing number of fungicide sprays in both years, but were not influenced by N application. Disease severity can be minimized through a combination of N and fungicide applications.