Fungal Leaf Spots: Fall Identification Guide

By James Wilson · September 30, 2026

Why Fungal Leaf Spots Surge in Fall

Cooler temperatures combined with increased moisture create ideal conditions for fungal pathogens. Dew formation and reduced airflow from falling leaves contribute to a spike in leaf spot diseases during autumn.

Common Fall Leaf Spot Diseases

Septoria Leaf Spot

Small circular spots with dark borders and tan centers, typically on lower leaves first. Common on tomatoes, chrysanthemums, and dogwood. Spreads rapidly in wet conditions.

Cercospora Leaf Spot

Larger spots with reddish-purple margins. Affects beets, Swiss chard, and ornamental plants. Centers may fall out creating a shot-hole appearance.

Anthracnose

Irregular brown or black spots that merge into large blotches. Common on maples, sycamores, and hostas. Often accompanied by leaf curl and premature drop.

Black Spot (Diplocarpon rosae)

Distinctive black spots with fringed margins on roses. Defoliation in severe cases. Fall cleanup is critical for preventing reinfection.

Diagnosis Tips

Check for concentric rings within spots (fungal fruiting bodies)
Look for tiny black dots within spots (pycnidia — spore-producing structures)
Fungal spots usually appear randomly, not uniformly across the leaf
Examine both leaf surfaces for sporulation

Organic Treatment Options

Remove and destroy affected leaves (do not compost). Improve airflow by thinning surrounding vegetation. Apply copper-based fungicide or neem oil. For roses, baking soda spray (1 tbsp per gallon) can slow spread.