Marssonina Leaf Spot
Marssonina spp.
11 host plants · Fungal
Last updated
This profile contains verified disease data from extension databases. Regional field notes and expert review are in progress.
Brown circular spots with distinctive dark rings appear on leaves, causing premature defoliation and weakening the plant significantly. This fungal disease favors wet conditions and spreads readily by rain splash and overhead watering. Remove fallen leaves promptly and regularly, improve air circulation, and avoid overhead irrigation to reduce humidity.
Leaf spot and blotch diseases are primarily cosmetic on established plants, though repeated years of heavy infection can weaken them. Rake up and remove fallen leaves to reduce the spore load going into the next season. Avoid overhead watering that splashes spores from the ground onto lower leaves. If the problem is severe, protective fungicide sprays during spring leaf emergence can help, but sanitation does more than chemistry for most leaf spots.
Quick Reference
Management
Spring and early summer (April-June); peak: late April through May. Emerging and young foliage most susceptible.
Spring; cool wet conditions (55-65°F) with 8-10 hours continuous leaf wetness. Rain-splash dominates dispersal. High humidity extends infection window.
Cultural Controls
- Space plantings and prune to improve air circulation.
- Prune and destroy infected twigs.
- Disinfect pruning tools after use.
- Rake and destroy (do not compost) infected leaves.