Cause Golovinomyces depressus has been reported from Idaho and observed many times in western Oregon on Centaurea montana. These are highly specialized pathogens that form a close association with the host. Conditions that favor the host also tend to favor the pathogen. Overcrowding of plants is also favorable for disease development.
Symptoms White colonies that are scattered and small at first but may cover entire leaves later. Lower leaves develop symptoms first, wilt and may stay on the plant or drop off early. Stems are also colonized.
Cultural control
- Good air circulation will help ensure uniform environmental growing conditions for the crop including both 'uniform' temperature and lighting.
- Keep relative humidity low.
- Remove and destroy infected plant parts if practical.
Chemical control Fungicides will do best when used before symptoms develop. Good coverage is essential. Fungal strains can become resistant to a fungicide when it is used exclusively in a spray schedule. To reduce the possibility of resistance, alternate or tank-mix fungicides that have different modes of action. Limit the use of any one group during the growing season.
- According to IR-4 data, Heritage is safe on some species of this genus. Use at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker on a few plants first before wide spread use. Group 11 fungicide. 4-hr reentry.
- Insignia SC at 3 to 6 fl oz/100 gal water. Do not use with organosilicate-based adjuvants. Use preventively only. Group 11 fungicide. 12-hr reentry.
- Pageant at 6 to 12 oz/100 gal water. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. 12-hr reentry.
- Seido at 4 to 5 fl oz/100 gal water plus an adjuvant. Group 50 fungicide. 4-hr reentry.
Reference Braun, U., and Mohan, S.K. 2013. New records and new host plants of powdery mildews (Erysiphales) from Idaho and Oregon (USA). Schlechtendalia 27:7-10.