Field Identification
If leaves, stems, or fruit suddenly look spotted, sunken, or rotting, cercospora leaf spot may already be active. This problem often starts small, then spreads across healthy tissue before most growers realize how serious it is. Warmth, moisture, and crowded foliage usually speed it up. Treat early, because waiting even a few days can turn a manageable infection into major crop loss.
Look for a pattern, not one bad leaf: expanding spots, dark or pale halos, fuzzy growth, or tissue that collapses when touched. Check both leaf surfaces, stem bases, and fruit scars where symptoms first appear. New lesions after rain, overhead watering, or heavy dew are a strong clue. When separate spots begin merging into larger dead patches, the disease is advancing quickly.
Not sure what you have? Use the symptom diagnosis tool →
How to Deal With It
Organic Control Methods
Bacillus subtilis and Pseudomonas products applied to leaves compete for infection sites when humidity is high -- anecdotal help, not a stand-in for rotation. Trichoderma soil drenches support root zone biology; leaf pathogens still need dry leaves. Strongest gains come from shortening leaf wetness, not from compost tea alone.
Scout lower canopy first; spores splash upward after rain. Deep plow or remove infected debris in intensive beet and chard rotations so inoculum does not volunteer next season. Begin protectant programs before forecast rains on susceptible cultivars.
Widen row spacing and orient rows with prevailing wind so leaves dry faster. Destroy crop residue after harvest; infected trash holds spores over winter. Rotate away from hosts for two years where feasible; short rotations stack disease faster than yields.
Drip irrigation keeps foliage dry; avoid late-day overhead watering that leaves leaves wet all night. In small gardens, prune lower leaves that touch soil and splash spores. Mulch with material that does not hold infected leaves against stems.
Copper and sulfur protectants follow label crops and rates -- apply before wetting events, not after lesions merge. Bacillus-based biofungicides add layers in humid seasons. Neem rotates as supplemental; test phytotoxicity on tender greens. Reapply after rain per label; protectant chemistry washes off.
Let Nature Handle It
Natural Enemies
- Bacillus subtilis
- Pseudomonas spp.
- Trichoderma spp.