Damping off: symptoms and prevention

Yesterday, your seedlings emerged. But today, some seem pinched at their base, as if burned. What happened ? Unfortunately, they are affected by damping off and are now unrecoverable. This basal rot is a common cryptogamic disease that decimates seedlings. Attacks on young shoots are caused by microscopic fungi. How to avoid this scourge of plantations? With these few tips, your next buckets may pass through!

Damping off symptoms

They have convoluted names: Botrytis, Fusarium, Pythium, Phytophtora or Rhizoctonia. They are cryptogamic fungi that attack your seedlings. How to spot an affected seedling? Just look at the base of the seedling: dehydrated, black or brown in color, it no longer holds straight. Stem shrinks and appears to have been pinched. Once the symptoms of damping off are detected, there is nothing more to do, as the affected plants will quickly die.

Although no plant is immune to damping off, certain vegetables in the vegetable garden are particularly affected by it: tomatoes, aubergines, carrots, onions, cucumbers, lettuce, cabbage and aromatic herbs. On the flower side, there are also predisposed varieties: nasturtium, dahlia, begonia and petunia are generally more affected.

Techniques to prevent damping off

The key to damping off is prevention. This fungus indeed develops with humidity and heat.

  1. Disinfect seeds
    To do this, soak the seeds in water at room temperature with wood chips. Leave for eight hours. Another faster, but more demanding solution is to immerse the seeds in hot water at exactly 48°C for 20 minutes. Do not exceed this temperature at the risk of losing germination.
  2. Disinfect the special sowing compost
    Spray part of the special sowing compost with a preventive fungicide treatment such as horsetail manure or nettle manure. As Quebec horticultural journalist Larry Hodgson suggests: “You can also sprinkle your potting soil with charcoal that you will have bought in a garden center (especially not the charcoal from the barbecue!). It’s a trick that is effective against damping off”.

  3. Disinfect the material using white vinegar.

semis in poquet
Credits: jcesar2015 / Pixabay

Planting tips

To avoid damping off as much as possible, follow these tips, tested and approved by experienced gardeners, such as Larry Hodgson:

  1. Use a special sowing soil (thin and light) capable of retaining water while being draining, often composed of perlite or vermiculite and sand. Absolutely avoid planting soil that is not suitable.
  2. Aerate and drain the soil at most. In pockets, fill with 2/3 of unsterilized soil and finish with 1/3 of sterilized soil on the surface. The seed germinates in the treated part, then after germination, the young roots establish themselves in the part of the non-sterile soil, where the biology is intact. Result: the rate of germination and growth without damping off varies between 75% and 80% on flower and vegetable seeds.
  3. When planting the seed, be sure to limit fertilizer applicationat the risk of grilling the young shoot.
  4. Respect the depth planting proper to the seed.
  5. Don’t plant when it’s too wet. Prefer cool, dry weather, but not too cold.
  6. Spray rather than watering to control the humidity level in the soil! Stagnant humidity obviously favors the proliferation of fungi.
  7. Cover sowing at night only.
plantation de semis
Credit: AnnaStills/iStock

Treatment after seedling emergence

If the disease has not appeared, it is possible to continue prevention by spraying the soil with horsetail manure or nettle manure. Lighten up the seedlings well after emergence, in order to avoid nutrient deficiencies and to guarantee the space necessary for the development of the plant.