Leaf Spot
Pathogen: Septoria, Cercospora, Alternaria spp. · Affects Tomato, Bean, Maize, Ornamentals
Leaf spot is really a family name for several closely related fungi that all produce the same telltale ringed lesion. It moves slowly compared to blight, so most growers first notice it as a gradual decline in lower-canopy leaves rather than a sudden crisis — which also means it is one of the easiest diseases to catch early with routine scouting.
Symptoms
- Circular brown or black spots with concentric rings
- Yellow halos around lesions
- Lower leaves defoliate first and progress upward
Causes
- Splashing rain and overhead irrigation
- Overwintering pathogens on crop debris
- Poor plant spacing
Treatment
- Apply chlorothalonil or mancozeb every 7–10 days
- Remove all infected leaves and destroy
- Mulch to reduce soil splash onto lower foliage
Prevention
- Rotate crops on a 2–3 year cycle
- Use drip irrigation and morning watering
- Sanitize tools and clear crop debris after harvest
Frequently asked questions
Is leaf spot the same as late blight?
No. Leaf spot lesions have distinct concentric rings and spread slowly from the bottom of the plant upward, while late blight causes irregular greasy patches that spread within days.
Why do lower leaves get leaf spot first?
Spores overwinter in soil and crop debris, so rain splash carries them onto the lowest leaves first before wind and further splash move them up the plant.
Preventive Fungicide Program
A rotating schedule of protectant contact fungicides for foliar diseases on vegetables, fruit and ornamentals.
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