Cause Two fungal-like organisms are reported to cause downy mildew on pansy: Plasmopara megasperma (formerly Bremiella megasperma) common in North America and Peronospora violae common in Europe and Asia. The disease has not been reported in the Pacific Northwest but has been observed in both Oregon and Washington. Wet, humid environments favor disease development. Under favorable conditions, the disease can spread quite rapidly, and the entire plant can droop and die. Oospores are formed in leaf tissue late in the season and serves as inoculum for the next season. Seed transmission is suspected but has not been proven.
Symptoms Sporulation of the organism may occur on the undersides of leaves with no symptoms above. Soon, upper surfaces of infected leaves show areas of slightly chlorotic discoloration. A light gray-brown, felt-like growth is on the undersides of infected leaves. Infected tissues become necrotic, and eventually leaves die.
Cultural control
- Grow tolerant or resistant cultivars.
- Use sterile soil or potting mix to start seeds.
- Destroy infected plants and debris.
- Inspect all plugs and cuttings for signs of infection.
- Avoid irrigation that lets plants remain wet a long time. Reduce humidity by using fans and ventilating the greenhouse after watering.
- Maintain adequate fertility.
- Rotate planting beds if replanting annually.
Chemical control Use before symptoms develop. Rotate fungicides with different modes of action to prevent the development of resistant organisms. Limit the use of any one group during crop production.
- Aliette at 1.25 to 4 lb/100 gal water. Group P7 fungicide. Do not use with adjuvants. 24-hr reentry.
- Compass 50 WDG at 1 to 2 oz/100 gal water. Do not use organosilicate additives. Group 11 fungicide. 12-hr reentry.
- CuPRO 5000 at 1.5 to 2 lb/A. Group M1 fungicide. 48-hr reentry.
- Fenstop at 7 fl oz/100 gal water. For greenhouse use only. Group 11 fungicide. 12-hr reentry.
- Fosphite at 1 to 2 quarts/100 gal water. Do not use copper products within 20 days of treatment and do not use spray adjuvants. Group P7 fungicide. 4-hr reentry.
- Heritage at 2 oz/100 gal water plus a non-silicone-based wetter sticker. 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.
- Micora at 4 to 8 fl oz/100 gal water. Group 40 fungicide. 4-hr reentry.
- Monterey Liqui-Cop at 3 Tbsp/gal water. H
- Monterey Garden Phos at 0.5 to 1.1 fl oz/gal water as a foliar spray. Also labeled for soil drench, see label for details. Group P7 fungicide. H
- Orvego at 11 to 14 fl oz/100 gal water. Group 40 and 45 fungicide. 12-hr reentry.
- OxiPhos at 1.3 to 4 quarts/100 gal water as a foliar spray. Group P7 fungicide. 4-hr reentry.
- Segovis at 0.6 to 3.2 fl oz/100 gal water plus another fungicide. Group 49 fungicide. 4-hr reentry.
- Stature SC at 6.12 to 12.25 fl oz/100 gal water. Group 40 fungicide. 12-hr reentry.
- Zonix at 45 to 76 fl oz/100 gal water. Can be sprayed on crop or injected into irrigation system. Short residual so may have to be used frequently for adequate results. 4-hr reentry.
Reference Hall, G. 1989. Perosnospora violae. CMI Descriptions of Pathogenic Fungi and Bacteria. No. 977.