Damping off

Damping off is a disease that affects emerging and young seedlings, causing them to collapse, keel over and die. They may also become covered in a whitish, furry fungal growth.

It can affect most seedlings, and is mainly a problem with seedlings arising from sowing indoors early in the year, but it will affect seedlings sown outdoors too.

Damping off is particularly a problem when seeds are sown in conditions of high humidity, where seeds are sown too thickly causing overcrowding and where there is poor air circulation around the seedlings. The disease is especially damaging in spring when low light levels and low temperatures, or anything else, cause plant stress and the seedlings are growing slowly. But it will occur at any time of year.

Pre-emergence damping off is also possible, where seedlings fail to emerge and grow at all.

• Seedlings

Damping off is a disease caused by several soil-borne fungi (Fusarium and Rhizoctonia) and fungus-like organisms (Phytophthora and Pythium). All are widespread in soil and elsewhere – including standing water.

They infect the soft and delicate tissues of young seedlings and kill them. Infection can occur after emergence of the plant from the seed, especially when humidity is too high and the seedlings are too closely spaced and crowded together, rapidly spreading from plant to plant, leading to collapse. The fungi may be visible as a whitish, furry growth or mould on the dying and dead plants.

Infection of the seed can also occur before the seedlings emergence (called pre-emergence damping off), which causes very patchy emergence.

Clean and sterilise growing conditions are essential to prevent damping off disease getting hold and killing young seedlings.

Always dispose of affected seedlings, including the compost they’re growing in. Put it in the council’s green waste bin. Don’t compost it.

It is always best to use bought sowing and growing composts. If you have to use home-made compost, it is worth steam sterilising it first to destroy any pathogens it may contain.

Sow seeds in new pots and trays or, if re-using old ones, wash and sterilise them with bleach or a disinfectant such as Jeyes Fluid first. Rinse thoroughly before using them.

Unfortunately, there are currently no fungicides approved for control of damping off.

Always sow seeds thinly to avoid overcrowding. Keep seedlings well ventilated to reduce humidity and don’t overwater them.

Preferably use tap water – that has reached room temperature – rather than stagnant or stored water from a waterbutt. If you use water from a waterbutt, make sure the waterbutt is cleaned out regularly to prevent the build-up of damping off organisms in the water.

• Seed trays
• Cell trays
• Pots
• Propagators