What is damping off? What can be done about it?

Damping off is a fungal disease caused by different pathogens. It is also called basal rot. It affects seeds and young shoots which, once affected, cannot survive. Countless plants can be affected by this very common cryptogamic disease, which is particularly feared by gardeners and producers.

Damping off: a fatal cryptogamic disease

Another name given to damping off is basal rot. It is a fungal disease caused by phytopathogenic fungi or oomycetes (pseudo-fungi). At the origin of basal rot, we most frequently find:

  • Pythium,
  • Botrytis,
  • Olpidium,
  • Sclerotinia,
  • Altenaria,
  • Phytophthora,
  • Fusarium,
  • Phoma

note that Pythium rises among the the most feared pathogenic fungi of gardeners and that it is the most common culprit of basal rot. However, regardless of the pathogen involved, this disease kills many growing plants and sometimes large circular areas can be seen in which all the seedlings are dead. There are therefore complete plant clusters that are affected since the person responsible passes very quickly from one plant to another through the pellicular water present in the earth.

Damping off: symptoms

Symptoms of this soil-borne fungal disease are numerous and vary depending on the causative fungus, allowing a keen eye to quickly identify the causative agent. From main events damping off, we can see:

  • The absence of germination of the seedlings and consequently an emergence which does not take place,
  • Plants germinate, but stems turn brown then thin,
  • A softening of the root system,
  • The detachment of the external root,
  • rotting of roots and stems,
  • Seedling death.

Whatever the symptom observed, the plant death affected by damping off or basal rot is irremediable.

The attack of the disease can take place at two different times, affecting plants at different times in their development cycle. So we can distinguish:

  • The pre-emergent pig iron or pre-emergence source : this is the early form of the disease since the pathogenic fungus is already present in the seed at the time of sowing. This can largely explain why many seeds fail to sprout.
  • The post-emergence castwe also talk about postemergency source : it occurs just after emergence. These are the embryonic form of the root or roots and the collet who are affected. Because of this alteration, the seedling wilts then dries out before collapsing because it has lost all its rigidity.

The amateur gardener can find himself totally helpless when, a few days to a few weeks after sowing, he finds himself faced with widely sparse boards where a few young shoots emerge here and there, even totally empty.

Damping off can affect countless plant species, either as seeds during the germination phase or at the seedling stage. It can be vegetable garden plants : cabbage, salad, squash, eggplant, onion, carrot, bean, tomato, cucumber… flowering plants or decorative foliage that are grown for their ornamental assets are also concerned, from lobelia to petunia, including datura, poppy and even begonia…

Thus, damping off is a fungal disease likely to rage in the vegetable garden, in the ornamental garden, but also in the orchard or even within large cereal crops. When it settles in important agricultural areas, basal rot can unfortunately lead to a significant financial loss.

Damping off or basal rot: main causes

The pathogenic fungi and pseudo-fungi responsible for damping off have a constitution allowing them to spend the winter without worry in the soil of the garden, under the waste and the dead leaves or in the seeds. When sowing is done, seeds and seedlings being very vulnerable, they cannot oppose the slightest resistance during the attack of basal rot.

However, for preserve seedlings and young shootsthe gardener can take certain precautions upstream in order to prevent the development of pathogens. It is enough to know the factors that promote damping off in order to be able to avoid them. It should therefore be noted that this fungal disease is favored by:

  • Stagnant water responsible for soil asphyxiation,
  • A humid environment
  • An ambient temperature below 10°C.

Damping off: prevention

It is known that cold combined with excessive humidity favors the development of pathogenic fungi and oomycetes. To prevent damping off, it is therefore recommended to:

  • Buy only very good quality seeds, even if it means paying a little more for them,
  • Discard damaged seeds because sowing them represents a considerable risk for all crops,
  • Always disinfect your gardening tools such as dibblers, seeders, watering cans, secateurs, but also pots, buckets, boxes, terrines, etc.,
  • Disinfect your hands before handling the seeds and young plants to be transplanted,
  • Spray the earth with a decoction of horsetail, a natural solution well known for its antifungal properties, which is also the case with garlic, which is used as an infusion and which also has antibacterial properties,
  • Do not sow the seeds too deeply and always follow the advice clearly indicated on the seed packets,
  • Sow clear, that is to say by spacing the seeds sufficiently to limit their density,
  • Only sow when the optimum conditions are met in order not to cause any delay in terms of emergence,
  • Ventilate well its frames, greenhouses, tunnels and other shelters daily for a few hours each at the sunniest moment and this, as soon as the sowing is carried out because the damping-off of the seedlings is even more rampant under little or no ventilated shelter,
  • Break up the soil well before sowing,
  • Only sow if the growing medium is perfectly draining, which amounts to giving preference to a well-adapted growing medium such as compost for seedlings which promotes drainage and is very light,
  • Get into the habit of not over-wetting the sown soil and prefer spraying the leaves of young shoots, making absolutely sure never to wet the seedlings excessively,
  • Proceed with the thinning as quickly as possible, especially when you have had a heavy hand at the time of sowing, the ideal being to eliminate the excess young shoots as soon as they emerge so that the others are sufficiently spaced,
  • Use the charcoal collected in the fireplace then reduce it to powder with a grater or with a hammer. Barbecue charcoal is strongly discouraged. Then simply cover a seeded board with a very thin layer of charcoal powder because this fuel absorbs excess water and many pathogens.

It is obviously essential to play the card of prevention rather than searching indefinitely for a remedy to cure his sick plants. This is all the more fundamental in the case of damping-off since there is no no cure to save the seeds in the germination phase or even the young shoots.

Finally, note that caution is required when gleaning seeds from your garden or fields in order to multiply your plants without breaking the bank. When autumn is cool and fogs and rains are very frequent, the risks of contamination of seeds by pathogens are high. Once at home, it is therefore very useful to examine the seeds rigorously and to eliminate without scruple all those which seem in bad shape in order to keep only the healthiest.

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