Cause Drepanopeziza populi-albae (formerly Marssonina populi or M. castagnei) and M. piriformis, fungi, have been reported form Oregon. In British Columbia M. brunnea f. sp. trepidae, M. castagnei, and M. populi have been found. The fungus M. brunnea f. sp. brunnea was found in Washington at the mouth of the Columbia River and in British Columbia. This last isolate was pathogenic only on hybrid poplars (TxD and DxN) but not on local aspens (Populas tremuloides). The disease is commonly found on Populus trichocarpa in Idaho. These fungi survive in fallen leaves or twigs infected the past year. The disease is most severe in wet weather and is common throughout the Pacific Northwest on aspen, cottonwoods and poplars.
Symptoms Brown flecks with yellow margins form on leaves and later turn to black spots. Acervuli initially appear as tiny blisters in the centers of spots. The fungus also may invade twigs. Severe infection may cause early defoliation and reduce growth.
M. populi produces bronze to chestnut-color leaf spots about 2 to 5mm in diameter. Spots coalesce into brownish black, vein-limited blotches.
M. castagnei produces dark brown to reddish brown spots with light-color centers about 3mm in diameter.
Cultural control
- Collect and burn leaves in fall.
- Avoid overhead irrigation that keeps trees wet for extended periods of time.
- Use resistant clones.
Chemical control Use in the spring when leaves begin to flush out and wet weather is forecasted. Applications work best before rainfall occurs.
- 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.
- Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. Group M5 fungicide. H
- 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.
- Mancozeb-based products. Group M3 fungicides. 24-hr reentry.
- Fore 80 WP 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.
- Ortho MAX Garden Disease Control at 2 teaspoons/gal water. H
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
References Newcombe, G. and Callan, B.E. 1997. First report of Marssonina brunnea f. sp. brunnea on hybrid poplar in the Pacific Northwest. Plant Disease. 81:231.
Spiers, A.G. 1978. An agar leaf-disc technique for screening the effectiveness and persistence of fungicides for control of Marssonina on Populus. Plant Disease Reporter 62:148-152.