University of Illinois Extension

University of Illinois Extension

Hort Answers

Fungal Disease

Marssonia Leaf Spots and Blights
Marssonia spp.

Marssonia leaf spot on black walnut.
Marssonia leaf spot on black walnut.
3 (1 = rare 5 = annual)
2 (1 = very little damage 5 = plants killed)
This disease affects Populus spp (poplar and aspen) and is more of a forestry disease than a landscape problem. However, with poplars growing in landscapes during prolonged wet weather, it can be a problem. Marssonia betulae causes anthracnose on birch trees and Marssonia thomasiana causes anthracnose on bittersweet.

Plants Affected
The spots/blotches on the foliage are brown. Badly infected leaves can turn all brown by midsummer (July) and be defoliated by August. Severe defoliation may cause the tree to leaf out again. The tree uses up part of its food reserves and becomes more prone to other diseases. In addition, late emerging new growth may not hardened off sufficiently and therefore may be prone to winter die-back. Badly defoliated trees tend to produce less new wood during the next one to two years.

Life Cycle
The fungus overwinters in the dead leaves or infected twigs. Spores are released in spring and cause infection as leaves emerge. Leaves on lower branches tend to be infected first and infection spreads upwards through the growing season.

There is no practical control for this disease in a forest setting. In the home landscape, follow good sanitation practices.

Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic