Description

Damping off or damping-off is a horticultural disease or condition, caused by a number of different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions.

Damping-Off  caused by Rhizoctonia in Groundnut

Damping-Off caused by Rhizoctonia in Groundnut

Damping off is caused by several soil-borne fungi including Pythium, Phytophthora, Rhizoctonia and Fusarium, which infect seedlings and cause them to “damp off” or collapse and decay.

Damping off can affect any seedling, particularly under high humidity levels, in cold wet soil, poor air circulation, poor soil drainage, use of green compost, and planting too deeply. Damping off is a huge problem when sowing seeds indoor early in the season or under glass, but can affect seedlings sown outdoors when specified conditions are prevalent.

Damage and Symptoms

Infected seeds don’t germinate; instead they turn mushy and brown. Seeds may be infected as soon as moisture penetrates the seed coat or a bit later as the radicle begins to extend, all of which rot immediately under the soil surface. This pre-emergence damping off results in a poor, uneven stand of seedlings, often confused with low seed viability.

Damping Off in sugarbeets caused by Pythemium fungi.

Damping Off in sugarbeets caused by Pythium fungi.

When seedlings are attacked after they emerge, stem tissue near the soil line decays, weakens and gets a dark, water-soaked area, usually causing the plants to topple over and die. When only roots decay, the plant may continue standing but will remain stunted, wilted and will eventually die.

Older plants that are infected have stem lesions that cause stunted growth, and can die.

Host Plants

Seeds and seedlings of most plants.

Organic Control and Prevention of Damping off

Prevention

– Cultural control of damping off diseases is based on providing favorable conditions for germination of the seeds and growth of plants while minimizing the conditions that favor fungi. This means growing seeds in well-drained soil, with adequate air circulation and dry conditions.

– Use sterile well drained soil mediums. Avoid wet or compacted soil. Raise seedlings in treated commercial growing compost. If home-produced compost is being used, steam-sterilize the compost to destroy pathogens. Soil mix has to be held at 140 deg. F for at least 30 minutes to ensure sterilization.

– Purchase disease free plants and seeds from a trusted supplier. Seed borne diseases can be avoided by soaking seeds for 15 minutes in bleach soak (1 teaspoon per quart of water) prior to sowing.

– In warm regions, practicing soil solarization can reduce pathogens in outdoor soil. To solarize, place clear plastic tarps over soil for extended periods.

– Use plant containers that have drainage holes, water from the bottom only and strictly avoid over-watering. Do not allow pots to stand in water as the excess water will starve the roots of oxygen.

– Ideally, use new pots and trays to raise seedlings. If re-using old ones, make sure to disinfect them thoroughly. Never reuse pots and trays in which damping off has been a previous issue.

–  As a rule of thumb, do not cover seeds with soil mix more than 4 times the thickness of the seed. Do not allow for the crowns of plants to be below the soil line.

– Use only well-decomposed compost. Do not use the green compost as its overly moist environment will encourage damping off fungi. Use well aerated composting soil to reduce chances of infection. Composted hardwood bark has been reported to reduce damping off.

– Cover seedlings with a thin layer of perlite, vermiculite, sand, or peat moss to keep the soil surface dry and keep fungal growth to a minimum.

– Avoid overcrowding and overfeeding of seedlings. Maintaining constant levels of growth through proper lighting and adequate control of growth environment is important and helps prevent damping off.

– Avoid working with plants (cuttings or transplants) when the soil is wet.

– Disinfect tools, containers and hands after working in areas that are likely to harbor damping off fungi.

– Drench starting soil mix with an anti-fungal agent. Chamomile tea, clove tea and garlic infused water have anti-fungal activity.

– Use water that you know is free from pathogens. Your mains water will mostly be safe for use on seedlings grown in pots and trays. If using rainwater, ensure that the water butt is covered to prevent the entry of leaves and other organic debris that could harbor pathogens.

– Remove and discard diseased plants.

– Avoid planting the same crops in the same place year after year.

Control

– Unfortunately infected seedlings usually die, but sometimes you can save the rest by improving growing conditions by making them as warm and dry as possible.

– Spray plants with seaweed extract as this will help strengthen them.

– Spray plants with Neem oil as it has anti-fungicidal properties as well as providing systemic benefits to the plant.

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