Cause The fungus Ciborinia whetzelii (formerly C. bifrons) incites this fairly common foliage disease. The fungus overwinters as sclerotia after falling from leaves. An apothecium emerges in the spring to shed spores that blow onto healthy foliage. Infection occurs during wet spring weather as new leaves are expanding. Brown foliage develops about a month later. Incidence is greatest in dense stands in the lower canopy of tall trees.
The fungus overwinters as sclerotia after falling from leaves. An apothecium emerges in the spring to shed spores that blow onto healthy foliage. Infection occurs during wet spring weather as new leaves are expanding. Brown foliage develops about a month later. Incidence is greatest in dense stands in the lower canopy of tall trees.
Symptoms Random clusters or patches of browned leaves with petioles remaining green. Circular to elliptical black sclerotia about 0.25 inch wide develop on the leaves after they turn brown. These sclerotia begin to fall out leaving the leaf with a shot-hole appearance. Severe defoliation may occur under heavy disease pressure.
Cultural control
- Collect and burn leaves in fall.
- Avoid overhead irrigation that keeps trees wet for extended periods of time.
Chemical control Use in the spring when leaves begin to flush out and wet weather is forecasted. Applications work best before rainfall occurs.
- 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.
- Daconil Weather Stik at 1.38 pints/100 gal at budbreak. Repeat at 7- to 10-day intervals if necessary. Group M5 fungicide. 12-hr reentry.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker. 24-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 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.