Alternaria Leaf Spot
Alternaria spp.
1 host plant
Last updated
This profile contains verified disease data from extension databases. Regional field notes and expert review are in progress.
Brown spots with concentric rings appear on leaves during warm, wet weather, causing defoliation. This fungal disease favors warmth and moisture. Remove fallen leaves and improve air circulation.
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 through early summer during cool, wet periods (March-June in Puget Sound region). Young, actively emerging leaves most susceptible. Infections less common in dry summers.
Cool, wet spring weather during leaf emergence. High humidity and leaf wetness favor spore germination and infection. Rain-splash dispersal critical for spread. Young, developing leaves most susceptible. Extended wet periods in spring favor rapid spread. No specific temperature optimum documented but cool-season fungi. # Source: PNW Plant Disease Management Handbook
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.