Septoria Leaf Spot
Septoria spp.
18 host plants · Fungal
Last updated
This profile contains verified disease data from extension databases. Regional field notes and expert review are in progress.
Small circular spots with dark borders and gray centers appear on leaves, causing yellowing and significant defoliation over time. This fungal disease spreads by rain splash and persists in fallen leaf litter on the ground. Remove fallen leaves and avoid overhead watering to reduce spread.
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. Young expanding leaves most susceptible.
Spring; cool wet conditions (50-65°F) with 8-10 hours continuous leaf wetness. Rain-splash dispersal. Successive wet periods drive multiple infection cycles.
Cultural Controls
- Remove and destroy infected leaves. Leaves may be composted if completely decayed before spring. Make use of any practice that encourages decomposition of fallen leaves prior to spring bud break, such as mowing or flailing. Apply urea to leaves after leaf fall in autumn to enhance decomposition of fallen leaves.
- Rake and destroy leaves in fall. Grow other, more resistant species of Crataegus.