What are the causes and treatment methods of cucumber damping-off disease?

Cucumber damping-off disease, commonly known as “neck strangling”, “little foot blight”, “seedling drop”, etc., is one of the common diseases during the cucumber seedling stage in winter and spring. When severe, it causes cucumber seedlings to collapse and die in patches. Damping-off mainly occurs after seedlings emerge in the seedbed. During the seedling stage, water-soaked spots appear on the base or middle part of the hypocotyl near the ground, later gradually turning yellow-brown and constricting around the stem in a ring to form a thread-like fold. The disease center is obvious. What causes cucumber damping-off disease? How is it treated?

1. What causes cucumber damping-off disease?

Because the suitable soil temperature for the growth of the pathogen is 15~16°C, and the growth of the pathogen is inhibited when the temperature is above 30°C, the suitable soil temperature for the onset of cucumber damping-off disease is around 10°C. This temperature is unfavorable for cucumber growth, but the pathogen can still be active. Especially during the seedling-raising period under low temperature and high humidity, the disease is most likely to occur.

The susceptible period is when the nutrients in the cotyledons of the seedlings have been basically consumed and the new roots have not yet become well established. At this time, the true leaves have not yet emerged, carbohydrates cannot accumulate rapidly, and disease resistance is weak. If rain, snow, prolonged overcast days, or cold waves occur at this time, the soil temperature drops and photosynthesis is relatively weak. Under such conditions, the respiration of cucumber seedlings increases, and the consumption of photosynthetic products (mainly carbohydrates) rises, causing the young stem cells of cucumber seedlings to elongate and the cell walls to become thinner, making them susceptible to pathogen invasion.

Therefore, cucumber damping-off disease mainly occurs easily when cucumber seedlings have grown 1~2 true leaves. After 3 true leaves have grown, the incidence rate drops greatly.

2. How is cucumber damping-off disease treated?

1. Seed selection is key

Low-temperature- and weak-light-tolerant, early-maturing cucumber varieties such as Yuanfengyuan No. 6 Green Cucumber, Zhongnong No. 7, Yuexiu No. 1, Zaoqing No. 2, and Zhongnong No. 8 can be selected.

2. Seeds must be properly disinfected

Seeds can be soaked and disinfected in warm water at 50°C for 20 minutes, or treated with dry heat sterilization at 70°C for 72 hours before germination and sowing. It is recommended to use cucumber seed coating agent No. 9-2 at a dosage of 0.5% of the seed weight.

3. Seedbed treatment must be appropriate

For the seedbed or greenhouse, apply more compost fermented with Japanese enzyme bacteria and reduce the amount of chemical fertilizers and pesticides. If necessary, the seedbed soil can be renewed, and compost fermented with enzyme bacteria or fully decomposed organic fertilizer can be applied. In production, soil from old vegetable gardens is often used as seedbed soil. 15~20 days before sowing, mix 40% seed-dressing ling powder with 50% thiram powder at a ratio of 1:1, or use 40% seed-dressing shuang powder, at 8 grams per square meter of seedbed, mixed with 40 kg of fine dry soil, and mix thoroughly for later use. Before sowing, water the bed thoroughly first. After the water seeps down, take 1/3 of the prepared medicated soil and spread it on the bed surface, then sow the pre-germinated seeds, and finally cover the seeds with the remaining 2/3 of the medicated soil, with a soil cover thickness of about 1 cm, so that the seeds are sandwiched in the middle of the medicated soil.

4. Strengthen seedling-stage management

After full emergence, keep the seedbed or greenhouse temperature at 25~30°C during the day and 10~15°C at night to prevent cold waves. Humidity in the seedbed or greenhouse should not be too high. During continuous rain or rainy and snowy weather, or when the bed soil is not dry, water less or not at all. When watering is necessary, use a watering can to water lightly to avoid excessively high humidity. When water droplets condense on the plastic film or glass and on the seedling leaves, ventilate promptly or sprinkle some plant ash to reduce humidity.

5. Chemical control

(1) Adding an appropriate amount of soil additive to the soil (made from rice husks, bagasse, shrimp shell powder, silicic acid furnace slag, etc., plus an appropriate amount of urea, superphosphate, potassium nitrate, etc.) can reduce the incidence of the disease.

(2) Use carbon dioxide fertilization technology, or apply Huimanfeng multi-element compound organic active liquid fertilizer at 320 milliliters per mu, diluted to a 500-fold solution, and spray twice.

(3) Mix 50 grams of copper sulfate and 375 grams of ammonium bicarbonate evenly, then add 100 grams of slaked lime. After mixing well, put it in a plastic bag, seal the bag opening, and keep it closed for 24 hours. Then add 5 kg of fine soil, evenly spread it over 10 square meters of seedbed. After spreading, rake and hoe the seedbed, brush off the medicated soil on the seedling leaves, and pay attention to ventilation to remove excess ammonia gas.