Cause The fungus Erysiphe adunca var. adunca (formerly Uncinula salicis) has been reported from British Columbia and the disease has been reported throughout the Pacific Northwest. Phyllactinia populi has also been reported from North America. Occasionally encountered on suppressed understory leaves of cottonwood and hybrid poplar.
Symptoms Dusty to cottony white clumps of superficial hyphae and conidia may engulf the entire upper leaf surface by the end of the growing season. Small orange to black globes (chasmothecia) may appear in these areas in mid to late summer.
Cultural control
- Space plants for good air circulation if possible.
- Removal and disposal of fallen leaves may be helpful.
- Plant in full sun.
Chemical control Fungicides will do best when used before symptoms develop. Few materials have good eradicant activity. Use at 7- to 14-day intervals; using shorter intervals when environmental conditions favor disease development. Alternate or tank-mix products from different groups that have different modes of action. Limit the use of any one group during crop production.
- 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 16 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
- Eagle 20 EW at 6 to 12 oz/100 gal water for nurseries or landscapes. Group 3 fungicides. 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.
- 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.
- Rally 40 WSP at 4 to 6 oz/A. Nursery or forest-area use only. Group 3 fungicides. 24-hr reentry.
- Tebuject 16 is registered for tree injections. The number of capsules used is based on tree size. Group 3 fungicide.
- Tourney EZ at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Reference Callan, B.E. 1998. Diseases of Populus in British Columbia: A Diagnostic Manual. Natural Resources Canada. Canadian Forest Service, Pacific Forestry Centre, Victoria, B.C. 157p.