Description and Control Methods
Symptoms
After Chinese cabbage is infected with damping-off, water-soaked lesions appear on the stem base near the ground.
The stem then shrinks, causing the seedling to collapse or wilt.
Under high humidity, white cottony mold grows on the infected parts or the soil surface.
Conditions for Disease Development
Damping-off is caused by
Pythium spp. such as
Pythium aphanidermatum.
The pathogen overwinters as oospores in the top 12–18 cm of soil and can survive for a long time.
In spring, under favorable conditions, it germinates to form sporangia, which infect the host via zoospores or germ tubes.
Hyphae living saprophytically in the soil can also produce sporangia, whose zoospores infect seedlings and cause damping-off.
Secondary infection in the field mainly comes from sporangia and zoospores produced on diseased seedlings, which are splashed by irrigation or rainwater onto the stems and roots near the soil surface.
The suitable soil temperature for pathogen growth is
15–16°C; growth is inhibited above 30°C.
The optimal soil temperature for infection is about
10°C.
Low temperatures are unfavorable for host growth but allow the pathogen to remain active.
Low temperature and high humidity during the seedling stage are especially conducive to disease occurrence.
Control Methods
To cultivate strong seedlings and prevent damping-off:
- Cover the seeds with a layer of nutrient soil after sowing.
- After watering thoroughly, cover with plastic film to maintain temperature and humidity.
- After emergence, spray with 0.2%–0.3% potassium dihydrogen phosphate 2–3 times to enhance disease resistance.
At the early stage of disease:
- Spray with 25% metalaxyl WP at 800× dilution.
- Or treat seeds with 75% chlorothalonil WP or 70% mancozeb WP.
- Or spray with 69% dimethomorph·mancozeb WP at 900× dilution.
