Archive:Poplar/Septoria Leaf Spot
From Bugwoodwiki
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From: Ostry, Michael E.; Wilson, Louis F.; McNabb, Harold S., Jr.; Moore, Lincoln M. 1988. A guide to insect, disease, and animal pests of poplars. Agric. Handb. 677. Washington, DC: U.S. Department of Agriculture. 118 p.
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Importance
Severe leaf infection may reduce growth potential by decreasing leaf photosynthetic area. Premature defoliation of highly susceptible trees is common. Spores produced in leaf spots can cause cankers on susceptible clones (see Canker Diseases).
Look For:
• Circular leaf spots up to one-half inch in diameter with brown or yellow margins. Black fruit bodies (pycnidia) are often present within spots.
• Irregular-shaped large spots with dark margins and tan centers. The spots may be target-shaped with pycnidia clustered in the centers.
• Small, angular leaf spots that often coalesce to form large spots.
• White, silvery spots, one-eighth inch in diameter
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| Ascospores in asci (sac-like cells). |
Biology
The fungus overwinters in infected, fallen leaves and in young stem cankers. In the spring, sexual spores (ascospores) from fruit bodies (perithecia) in the fallen leaves are released during wet weather. Wind and rainsplash carry these spores to leaves, branches, and stems, where infection takes place. Asexual spores (conidia) develop in these primary infections and are rainsplashed to adjacent leaves and stems, causing secondary infections.
Monitoring
Examine trees for leaf spots in early summer and new cankers in mid-summer to late summer. Cankers are most visible after leaf fall.
Control
• Plant only uninfected nursery stock because this fungus can become established early in plantings if infected stock is planted.
• Harvest highly susceptible trees early and replant with resistant clones.
Susceptibility to Septoria differs by clone. Plant only resistant clones. Generally, P. X euramericana clones are more resistant than clones with P. trichocarpa as a parent.
For Additional Information:
Ostry, M.E. 1987. Biology of Septoria musiva and Marssonina brunnea in hybrid Populus plantations and control of Septoria canker in nurseries. European Journal of Forest Pathology. 17: 158-165.
Ostry, Michael E.; McNabb, Howard S., Jr. 1986. Populus species and hybrid clones resistant to Melampsora, Marssonina, and Septoria. Res. Pap. NC-272. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 7 p.
Ostry, M. E.; McNabb, H. S., Jr. 1985. Susceptibility of Populus species and hybrids to disease in the north central United States. Plant Disease. 69: 755-757.
Palmer, Marguerita A.; Schipper, Athur L.; Ostry, Michael E. 1980. How to identify and control Septoria leaf spot and canker of poplar. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 6 p.
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| Conidia |
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| Partially defoliated tree (left) compared to resistant tree. |
