Treatment, diseases

Armillary or root rot: a destructive fungus

Armillary or root rot: a destructive fungus

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The armillary (or root rot) is a disease caused by a mushroom which attacks woody plants, that is, woody plants.

Its ease of spread and its insidious nature make it a formidable parasite capable of destroying many plants. Get to know this invisible enemy in order to better identify, treat and prevent it.

  • General
  • Symptoms
  • Control and treatment
  • Prevention

General information on the armillary

Root rot biology:

To fully understand armillaria disease, it is important to know the fungi biology. Indeed, what is commonly referred to by the term "mushroom" is in fact just a fruit (the carpophore) from an underground part called the mycelium. The latter is composed of many filaments, branched and generally white. It can cover more or less important surfaces.

This distinction between mycelium and fungus is essential, because it allows to better define the way in which this parasite is reproduced and this spread.

In addition, it is necessary to understand that an absence of fungi does not necessarily mean that the underground mycelium is inactive. Thus, many plants can die from root rot before seeing the mushrooms appear.

Propagation of the armillaria:

Armillaria can infect new hosts in many ways. It can indeed be transmitted to healthy subjects by simple contact with diseased roots.

The second contamination process is much more insidious since it takes place underground. These are blackish cords resembling roots and are called rhizomorphs. These are between 15 and 45 cm deep and can travel 1 m per year. It is therefore not uncommon to see contaminated plants located tens of meters from the infection strain.

These modes of propagation therefore make armillaria a formidable pathogen.

What plants are concerned?

There are two types of diseases: broadleaf armillaria (Armillaria mellea) and softwood armillary (Armillaria ostoyae).

You got it, the fungus touches the woody plants, that is, made of wood. Unfortunately, no plant is 100% immune to this parasite. However, some of them show some resistance to disease:

  • For shrubs: boxwood, fuchsia, lavender, rosemary, pittosporum, abelia, camellia, andromeda, hydrangea, jasmine, hibiscus, etc.
  • For trees: mimosa, albizia, fig tree, ginkgo, bay leaf, yew, olive tree, plane tree mulberry, strawberry tree, pear tree, Indian lilac, etc.

If you want a more complete list:

  • Sensitivity of plants to armillaria

Symptoms of armillaria

Armillary infection can be identified by symptoms direct (aerial parts of the plant) and indirect (underground parts).

Direct symptoms (underground):

When affected by the disease, the infected subject presents dead roots and decaying. We can also observe white filaments (the mycelium) between the bark and the wood of the roots, accompanied by a odour mushroom characteristic. The part just above the ground, called the collar, may also be affected. The trunk, meanwhile, can also be contaminated over 1 m, but this is rare.

Detect the parasite by its rhizomorphs is possible, but complicated (because of their depth and their color that blends into the earth).

Indirect symptoms (foliage, branches, fruits, flowers):

Because root rot causes root system failure, the infected plant may show signs of wasting away :

  • smaller, pale leaves;
  • an absence of flowering;
  • Conversely, unusually abundant flowering and fruiting (which often precedes plant death);
  • branches that die;
  • cracking and bleeding of the bark at the base of the stems;
  • foliage showing premature fall colors;
  • an appearance of fungi in the fall, if conditions permit.

Note that a particularly hot and dry summer can make these symptoms worse.

Control and treatment

Unfortunately, there is no no chemicals to fight against the armillary. When its presence is confirmed, the only way to get rid of it is to dig so to extract all infected roots and / or stumps and burn then. The rhizomorphs will then be deprived of their food source and can no longer develop.

Prevent the appearance of armillaria

To prevent root rot, the first solution is to do not plant sensitive plants fungus in risk areas.

A regular tillage and in depth helps break rhizomorphs and limit their spread.

As with many diseases, hygiene is important. Thus, it is strongly recommended to disinfect all your tools after carrying out your work in the garden or vegetable patch.

For high-risk areas, a radical technique helps prevent the spread of armillaria. It consists in burying a physical barrier over 45 cm minimum depth and protruding 2 to 3 cm from the ground. You can use an anti-rhizome barrier, or any other plastic obstacle, for this. The important thing is that it can withstand burial.

Video: Naked long stem Fungus Diseased Vanda with few leaves Orchids Rerooting (August 2022).