Preventing damping off disease

A zinnia seedlings which has gone brown at the base of its stem

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It looks like we’ve been visited by damping off disease. We found this little zinnia seedling flopped over, and going brown from the base of the stem upwards.

It looks as though we have been lucky in that we only seem to have lost three zinnia seedlings to date. It can wipe out a patch of seedlings in a tray or spread to the whole tray or beyond.

What causes damping off?

Damping off is caused by several types of organism, particularly certain types of fungi and bacteria. They live in the soil and are usually carried by water.

You might see fine fluffy white threads of fungus on the surface of the compost or on the affected seedlings. But sometimes the only thing you’ll see is the dead or dying seedlings. Or you may find that a tray of seeds has only come up in patches because the rest have been affected as they germinate.

The organisms that cause the disease are widespread in soil so it can affect seedlings planted outside. But it is the growing conditions that we create in the greenhouse that can encourage it to spread: damp, warm, humid conditions with a high concentration of seeds.

What can you do to prevent or cure damping off?

It used to be that there was a copper-based treatment but this was deregulated in 2012. So, there are now no longer any treatments available for the domestic gardener in the UK.

What you can do is try to reduce the likelihood of it occurring with a bit of good housekeeping. Here are our top tips:

Do

  • Disinfect the greenhouse regularly using a product suitable for a garden situation – in other words one that won’t poison your plants. For example, Citrox*, Vitax Greenhouse Disinfectant* or Jeyes fluid*.
  • Wash/disinfect pots, trays, tubs, capillary matting, etc thoroughly before you reuse them
  • Use commercial compost – although not entirely sterile, the chances of infection are greatly reduced
  • Watch your temperature control – use a raised temperature for germination, move seedlings to an area with a lower temperature for growing on

Don’t

  • Use rain water or water from water butts
  • Reuse compost
  • Plant seedlings too densely – check the packets for advice on spacing for each variety
  • Over water

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