How to Prevent and Control Damping-Off Disease in Seedling-Stage Nursery Stock

Damping-off disease of nursery stock occurs commonly throughout China. It mainly harms the seedlings of various nursery plants and flowers and can cause the death of nursery stock. So how do you prevent and control damping-off disease in the seedling stage of nursery stock?

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I. Symptoms and Causes of Damping-Off Disease in Nursery Stock

1. Symptoms

When seeds or young buds are infected before they emerge, they rot. When the disease occurs at the seedling stage, water-soaked lesions appear on the stem base at or below the soil surface. The diseased area is yellowish-brown and constricted, and can spread upward and downward through the plant in a linear pattern. The disease progresses rapidly, the tissue disintegrates, and the young stem immediately wilts and lodges, but the leaf edges remain green for a short time. If the environment is humid, white cottony mold also grows on the diseased area and the nearby soil surface.

2. Causes

The pathogens are some fungi in the genus Pythium. The common ones are Pythium aphanidermatum and Pythium debaryanum. The minimum growth temperature of these two Pythium species is 5 to 6°C, the optimum temperature is 26 to 28°C, and the maximum temperature is 36 to 37°C. High humidity makes disease development very likely, and they have strong saprophytic ability, able to live saprophytically for 4 years on parasitic residues in the soil. Pythium is a soil-inhabiting fungus, living saprophytically in the soil for long periods and forming oospores to survive unfavorable conditions. It is a soil-borne disease, mainly surviving as oospores in the soil and as mycelium saprophytically on diseased residues or other organic matter in the soil, overwintering after being mixed into compost. The pathogen is mainly spread by water and by people's gardening operations.

3. Conditions for Disease Development

High humidity is the main condition for seedling disease development. In the Yangtze River basin of China, there is a plum rain season in May and June, which favors the growth, development, and spread of the pathogen, but is unfavorable for seedling growth, leading to reduced disease resistance in seedlings and worsening of the disease.

In addition, insufficient sunlight, continuous cropping, improper selection of nursery land (such as low-lying terrain, heavy clay soil, or land where damping-off disease has occurred before without thorough disinfection), poor land preparation, application of compost mixed with pathogens that has not been fully decomposed at high temperature, and improper sowing and harvesting can all lead to disease development.

II. Prevention and Control Methods for Damping-Off Disease in Nursery Stock

1. Choose Good Nursery Land

It is best to choose mountain land and newly reclaimed land for raising seedlings, avoiding continuous cropping, so that there are fewer pathogens in the soil and the disease is mild. If cultivated land is used for raising seedlings, the previous crop should preferably be legumes or oak seedlings. Land intercropped with susceptible plants such as eggplant, melons, cotton, and potatoes should not be used as a nursery, or else seedlings should be raised after disinfection. Places with too high a groundwater level or poor drainage should also not be chosen as a nursery. If seedlings are raised in nursery land with poor drainage, drainage ditches should be dug well, higher seedbeds should be made, and the bed surface should be level to avoid water accumulation.

2. Soil Disinfection

On acidic soil, while preparing the land, spread 20-25 kg of quicklime per 667 sq m to inhibit pathogen reproduction in the soil and promote the decomposition of plant residues. In areas where firewood and grass are more convenient, the surface soil can also be burned to eliminate pathogens in the surface soil. In areas where the surface soil cannot be burned, chemical treatment can be used on the soil.

3. Decomposed Fertilizer

Organic fertilizers, especially garbage fertilizer and compost, often carry pathogens and should be piled for fermentation and fully decomposed before use.

4. Careful Land Preparation

Nursery land should be deeply plowed and carefully prepared. Before sowing, place a 1 cm thick layer of subsoil or burned soil in the drill furrows. After sowing, cover the seeds with subsoil or burned soil. Because subsoil and burned soil do not carry bacteria, they can isolate the seeds from pathogens, prevent seed buds from rotting, protect seedling roots and stems from pathogen attack, and prevent damping-off disease in seedlings. As seedlings gradually grow, the seedling stems have already formed a cuticle and cork layer, and disease resistance is enhanced. Although root rot may still occur, it will not spread into a disaster. Subsoil easily hardens after rain and cracks in the dry season, so it should not be too thick, preferably not exceeding 1.5 cm. The thickness of the subsoil cover should be such that the seeds are partly hidden and partly visible.

5. Sow Early at the Right Time

Sowing early at the right time means seeds germinate earlier, root more deeply, grow robustly, and have strong disease resistance. But if sowing is too early, the soil temperature is low, the seeds cannot germinate, and the seeds remain in the soil too long, making seed bud rot likely. If sowing is too late, seedlings are prone to damping-off disease if they encounter rain after emergence.