Root rot is a disease linked mainly to a microorganism, the Phytophtora, literally "plant destroyer" in Greek. This disease can affect a large number of plants, such as yew, rhododendron, azaleas, piéris and also in recent years ornamental conifers such as chamaecyparis and thuja.
Recognize root rot
If there are many species of Phytophtora, it seems that cinnamomi is most involved in rot by introducing itself at the roots or the collar, this being the starting point of the stem. The root system is reduced, the rot accompanied by chancous sores. Sometimes the rot is brown and spongy, especially at the neck of some conifers. The roots can no longer play their essential role of supplying water and nutrients, consequently the foliage discolours, browns or reddens, then dries up. If the parasite strain is highly phytopathogenic, the plant dies quickly.
Biology of Phytophtora
The Phytophtora were once assimilated to a family of fungi, because of their resemblance to mycelium, but advances in biology have revealed many differences in metabolism and sexual reproduction mechanisms, which has led to the Phytophtora being brought together. brown algae. This genus, Phytophtora, includes more than a hundred species and belongs to the Oomycetes of the Straménopiles group. Phytophtora keeps for a long time in soil and in sick plants. It develops in conditions of persistent humidity, during too frequent watering or excessive drip (especially in container crops), and with a temperature around 15 - 16 ° C. The spread of this parasite is through rivers, watering, certain farming practices, transport of agricultural products ... Contamination is favored by injuries to the collar or surface roots.
Other agents of root rot
Other parasites, whether or not close to Phytophtora, exert their harmful action on the seedlings of market garden species, such as endive, spinach. We then speak of damping-off of seedlings. Still others focus more particularly on indoor plants, such as cyclamen, croton, poinsettia.
Preventive and curative measures
Root rot is a very serious disease and almost impossible to treat, which is why, in order not to promote the pathogen, it is necessary to take cultural precautions, of which here is a summary. Avoid excess water in the soil and possibly install drainage. Choose treated seeds and healthy and vigorous plants. Be careful not to injure the collar and roots. For container culture, prefer a bed of gravel to a plastic film to place the pots. Disinfecting the soil is sometimes essential in intensive crops (by heat and / or chemicals). Avoid hedges of a single species in shrub plantations. Burn affected subjects and never replant sensitive species in the same place. By C. Schutz Croué