Description and Control Methods
Symptoms
Alternaria leaf spot of Chinese cabbage is a
systemic fungal disease.
It mainly infects the leaves, starting from the seedling stage, and is most severe during the middle and late rosette stages, affecting head formation and quality.
Infection is usually most serious on the
lower and middle leaves; small lesions may also appear on the top of the inner leaves in severe cases.
Initially, small black spots appear on the leaves, which gradually expand into dark brown lesions with concentric rings.
The centers of lesions may crack or perforate.
Under high humidity, mold grows on both sides of the lesions.
Affected parts or entire leaves turn yellow and scorched.
Conditions for Disease Development
The occurrence of Alternaria leaf spot is related to climate, cultivar resistance, and cultivation management.
High temperature and high humidity favor disease development.
Epidemics easily occur at about 17 °C with continuous rain or fog.
Disease severity varies among cultivars.
Early-sown crops are more severely infected than late-sown ones.
Over-irrigation and insufficient basal fertilization increase disease incidence.
Seed treatment before sowing reduces infection in the seedling and mid‑late growth stages.
Field observations show that the disease is most severe on outer leaves, less on head leaves, and mildest on inner leaves.
Older lower leaves are infected earlier and more severely.
Infection spreads
upward from the lower leaves and inward from outer leaves.
Control Methods
Integrated control should be adopted, focusing on agricultural control, combined with resistant cultivars and timely fungicide protection.
Crop rotation and field sanitationAlternaria leaf spot attacks a wide range of cruciferous vegetables.
Continuous cropping of crucifers increases disease severity.
Rotate with
legumes, cucurbits, or solanaceous crops.
Clean fields promptly after harvest to reduce inoculum.
Improve field management
- Timely thinning and final planting: retain vigorous seedlings.
- Formula fertilization:For a target yield of 10 000 kg per mu, apply 5000 kg fully decomposed farmyard manure and 50 kg phosphate fertilizer before sowing.Topdress during seedling, rosette, and heading stages with 16 kg N, 8 kg P₂O₅, and 18 kg K₂O per mu.
- Irrigation: light and frequent irrigation at seedling stage, proper water control at rosette stage, sufficient water and fertilizer at heading stage; avoid flooding.
- Sowing date: appropriate late sowing (about one week before Start of Autumn) without reducing head formation.
Use resistant cultivarsIn the county, highly resistant, high‑yielding and storable cultivars include
Qingza Zhongfeng, followed by
Fengkang 78,
Fengkang 79,
Fengkang 80, etc.
Seed treatmentTreat seeds with
0.3%–0.4% of 75% chlorothalonil WP or 70% mancozeb WP to kill seed‑borne pathogens.
Chemical controlApply fungicides immediately when
initial infected plants appear, at 7–10‑day intervals, 2–3 times total.
Recommended fungicides:
- 50% iprodione WP, 1000× dilution
- 75% chlorothalonil WP, 600× dilution
- 70% mancozeb WP, 600× dilution
- 64% oxadixyl·mancozeb WP, 500× dilution