Occurrence of chrysanthemum downy mildew in Nara prefecture and its control with thermotherapy and fungicide

• Published in: Annual Report of The Kansai Plant Protection Society Vol. 61; pp. 79 - 84
• Main Authors: Yoshida, Kandai, Asano, Shunsuke, Sumikawa, Yuka
• Format: Journal Article
• Language: English
• Published: The Kansai Plant Protection Society 31.05.2019
• Subjects: disease occurrence; fungicide control; hot water treatment; Peronospora danica
• ISSN: 0387-1002; 1883-6291
• DOI: 10.4165/kapps.61.79

In 2017, chrysanthemum downy mildew, which has not been reported in Japan since 1980, severely affected chrysanthemum production in Nara Prefecture, Japan. We investigated the occurrence of the disease at the fields in Nara Prefecture and the control efficacy of thermotherapy and fungicides against it. In the field survey, over 95 % of plants were diseased in seven cultivars, while no plants with the symptoms were observed in the other six cultivars. This suggests that some chrysanthemum cultivars had resistance to downy mildew. Chrysanthemum cuttings were treated with thermotherapy (treatment with hot water and hot air). The disease prevalence in both treatments was significantly lower than that in the non-treated. Severely diseased plants were sprayed with three fungicides (azoxystrobin, manzeb, and tolfenpyrad). While azoxystrobin and manzeb reduced the disease severity compared with non-treated, its efficacy was not so high. We concluded that the use of resistant cultivars and the application of thermotherapy can effectively control chrysanthemum downy mildew.