Cause Several fungi have been reported from the Pacific Northwest including Alternaria sp. (leaf spot), Ascochyta syringae (leaf blight), and Phyllosticta sp. (leaf spot). Airborne or water-splashed spores infect young leaves during wet weather, in the spring.
Symptoms Light-brown to dark-brown necrotic leaf spots and blights.
Cultural control
- Space plants or prune branches for good air circulation.
- Avoid overhead irrigation or anything that will contribute to leaves being wet for extended periods of time.
Chemical control These are registered for lilac and may be helpful.
- Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. Group 3 + 11 fungicide. 12-hr reentry.
- Banner MAXX at 5 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
- Compass 50 WDG at 2 to 4 oz/100 gal water. Do not use organosilicate additives. Group 11 fungicide. 12-hr reentry.
- Daconil Weather Stik at 1.38 pints/100 gal water. Group M5 fungicide. 12-hr reentry.
- Eagle 20 EW at 6 to 12 fl oz/100 gal water. Group 3 fungicide. 24-hr reentry.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
- Myclobutanil 20 EW T&O at 6 to 12 fl oz/100 gal water plus spreading agent. May observe a PGR effect. Group 3 fungicide. 24-hr reentry.
- Orkestra at 4 to 10 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Pageant at 4 to 12 oz/100 gal water. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. 12-hr reentry.
- Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 1 fl oz/gal water. Group 3 fungicide. H
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
- Tourney EZ at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Reference Pscheidt, J.W., and Moorman, G. W. 2001. Chapter 56. Lilac Diseases p. 221-224 in Diseases of Woody Ornamentals and Trees in Nurseries, R. Jones, and M. Benson (eds.). St. Paul, MN: APS Press