See:
Poplar (Populus spp.) - Leaf and Shoot Blight
Poplar (Populus spp.) - Bacterial Blight
Cause The fungus Venturia macularis (formerly V. tremulae) is found on aspen (P. tremuloides). This fungus overwinters in infected shoots but not in leaves. Spores are produced in wet spring weather, ascospores ejected from overwintered pseudothecia and overwintered conidia. Immature and young shoots are susceptible to infection but become resistant as tissues age.
Shoot blight with similar symptoms has also been found on aspen due to the bacterium Pseudomonas syringae.
Symptoms A variety of brown to black leaf spots and blights on leaf tips and margins. Necrotic areas expand rapidly; killing whole leaves and shoots. Shoot dieback is characterized by a "shepherd's crook" appearance of the blackened terminals. Lesions generally do not extend into woody tissues. Velvety mats of olive-green conidia occur on leaf spots and shepherd's crooks. Affected tissues dry out and become brittle. Disease impact is greatest on younger trees. Repeated blighting for several years results in stunted and malformed trees. Spring frost damage can be confused with shoot blight but frost damage is usually found more widespread and higher up on trees.
Cultural control
- Prune out infected shoots.
- Plant resistant clones.
- Avoid overhead irrigation that keeps trees wet for extended periods of time.
Chemical control Use any one of these fungicides during early shoot growth in spring. Use copper-based materials for bacterial caused disease.
- 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 is registered for other pests and may be effective against this one. Group 3 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. See special eye irritation provisions on the label. 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.
- 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.
- Junction at 1.5 to 3.5 lb/A. Group M1 + M3 fungicide. 48-hr reentry.
- Mancozeb-based products. Group M3 fungicides. 24-hr reentry.
- Fore 80WP Rainshield at 1.5 lb/100 gal water plus a spreader-sticker.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
- Phyton 27 at 1.5 to 3.5 oz/10 gal water. Group M1 fungicide. 48-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-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 Newcombe, G. 2003. Native Venturia inopina sp. nov., specific to Populus trichocarpa and its hybrids. Mycological research 107:108-116.