Look For:

• Small, brownish, circular to angular spots one-eighth inch across, often with a chlorotic halo caused by M. brunnea, the predominant species of poplars in the North Central States.
• Large, angular, rust-brown to black blotches characteristic of other Marssonina species or of M. brunnea when spots coalesce.
• Whitish masses of conidia in centers of spots.
• Lens-shaped lesions with white centers on leaf petioles and new growth.

Biology- Marssonina overwinters in lesions on the new shoot growth and in fallen infected leaves. Ascospores produced in leaf debris and conida from lesions on the previous year's shoot growth are released in the spring during wet weather, infecting leaves and new shoots. Conida produced in these new leaf spots and lesions are rainsplashed to adjacent leaves, causing secondary infections that can become epidemic in midsummer to late summer.

Control:

• Plow under leaf debris in late fall or early spring to reduce inoculum in plantations.
• Avoid introducing the fungus to new areas by closely examining planting stock for lesions and destroying infected cuttings.
• Clones differ in susceptibility to Marssonina, so plant only resistsant clones.

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, M. E.; McNabb, H. S., Jr. 1983. Diseases of intensively cultured hybrid poplars: a summary of recent research in the north central region. In: Hansen, Edward A., comp. Intensive plantation culture: 12 years research. Gen. Tech. Rep. NC-91. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station: 102-109.

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.

Ostry, Michael E.; McNabb, Harold 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.

Palmer, Marguerita A.; Ostry, Michael E.; Schipper, Arthur L., Jr. 1980. How to identify and control Marssonina leaf spot of poplars. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 5 p.

Spiers, A. G. 1983. Host range and pathogenicity studies of Marssonina brunnea to poplars. European Journal of Forest Pathology. 13: 181-196.

Spiers, A. G. 1984. Comparative studies of host specificity and symptoms exhibited by poplars infected with Marssonina brunnea, Marssonina castagnei, and Marssonina populi. European Journal of Forest Pathology. 14: 202-218.