What it is
This is most likely Cercospora leaf spot (frogeye leaf spot) of pepper, caused by the fungus Cercospora capsici. It produces circular to oblong spots with light grey or tan centres and dark brown margins, resembling a frog's eye, on leaves, stems, and stalks. Severe infection causes yellowing and defoliation, exposing fruit to sunscald. Fruit is usually not infected but can be smaller.
Symptoms to look for
- Circular to oblong leaf spots with light grey or tan centres and dark brown margins
- Spots resemble a frog's eye; concentric rings may appear as they enlarge
- Centres may crack and drop out, leaving a shot-hole look
- Spots on stems, petioles, and stalks; heavy spotting yellows leaves
- Defoliation exposes fruit to sunscald; fruit is usually not directly infected
When it spreads
Warm, wet, humid conditions (optimum around 23 to 27 degrees C with 77 to 85% humidity) and prolonged leaf wetness. It is especially damaging in tropical and subtropical regions. The fungus survives on seed, in soil, and on crop debris, and spreads by wind, rain splash, tools, and workers.
Treatment
Field practices
Use a two-to-three-year rotation between solanaceous crops, plant clean, pathogen-free seed, inspect and discard diseased transplants, use drip rather than overhead irrigation, space plants for airflow, and remove crop debris after harvest.
Organic options
Remove and destroy infected leaves and debris. Copper fungicides and Bacillus subtilis biofungicides protect healthy foliage when started early and repeated every 7 to 10 days in wet weather. Mulch and improve airflow to keep foliage dry.
Active ingredients
- copper hydroxide
- copper oxychloride
- Bacillus subtilis
Chemical options
Protectant fungicides such as chlorothalonil or mancozeb on a 7 to 14 day schedule give good control, especially preventively; products with azoxystrobin or difenoconazole are also effective. Alternate modes of action to slow resistance and cover lower leaves well.
Active ingredients
- chlorothalonil
- mancozeb
- azoxystrobin
- difenoconazole
Safety
Wear gloves, a mask, and eye protection when spraying fungicides, and follow the label pre-harvest interval before picking. Keep children and animals away from treated plants until dry, avoid drift onto food crops, and store chemicals safely out of reach.
Preventing it next season
Use clean, certified seed and resistant varieties where available, rotate crops, keep foliage dry with drip irrigation and good spacing, remove crop debris, and scout early since warm, wet weather drives rapid spread.