Black rot on an orchid: Cause, Symptoms, Treatment, and Prevention

The disease of a beloved flower, nurtured with such patience and care from a small sprout that arrived from a distant abroad in a flask, is always a very big annoyance and a lot of trouble for an orchid. Black rot on an orchid is one of the most dangerous pathologies and is treated only in the initial stages of the onset of the disease.

It is most often found on plants of the Cattleya and Paphiopedilum genus, and 70% of diseased orchids are from newly arrived flowers that have made a long journey from a foreign greenhouse to the buyer’s house. However, other types of orchids are not immune from this scourge, for example, black rot in the phalaenopsis orchid is also a common occurrence. Lelia, stanhope, and leliokattleya were also at risk.

What does black orchid root rot look like?

What Does black Orchid Root Rot Look Like?
black orchid root rot

The disease often manifests itself extremely quickly. In the evening, nothing portends trouble, and in the morning the young sprouts at the base of the plant turned black, became slippery, and fell off.

Sometimes, very rarely, black rot manifests itself in slightly different signs the rhizome, the bases of adult tuberidia (pseudobulb) and the lower part of the stem begin to rot.

What causes black rot?

The main “culprit” of the disease in 90 cases out of 100 is the fungus Pythium ultimum. In addition to it, other fungi are also the cause of black rot – Phytophthora omnivore, Pythium debaryanum. Pathogens are especially activated in favorable conditions for it, namely:

  • regularly waterlogged soil mixture and, as a result, its compaction, loss of looseness, and air permeability;
  • a decrease in the acidity of the growing medium, that is, the pH level exceeds 6-6.5, which indicates the neutrality of the substrate or its alkalization;
  • an excess of nitrogen in the substrate, resulting from overfeeding the orchid: too frequent fertilizers or overestimation of their dose;
  • constant high air humidity with irregular ventilation;
    thermometer readings in the room do not drop below 20 degrees at night and less than 30 degrees during the day;
  • overheating of the substrate and, accordingly, the root system in plants that are in a room where for a long time the temperature is kept in the range from 25 to 33 degrees of heat and other reasons.

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How to prevent black rot on Orchid?

How To Prevent Black Rot On Orchid

Each orchivode, as a recommendation for the prevention of fungal diseases, will first of all indicate the observance of the rules for the care and maintenance of an orchid at home. To prevent black rot on an orchid, the following mandatory preventive measures are important:

  • adhere to the correct balanced regimen of moistening orchids in the home collection – after drying the substrate only with warm water at room temperature;
  • constantly ventilate the room where orchids grow, providing a regular supply of fresh air;
  • monitor the level of illumination, if it is insufficient, organize additional illumination with phytolamps, especially in the winter period, when daylight hours are significantly reduced;
  • observe the feeding regime appropriate for this type – use only specialized fertilizers for orchids and in no case use those complexes that are intended for ordinary domestic plants growing in the ground;
  • constantly observe your orchids, regularly inspect them, carefully examining the inner areas of the leaf axils, growth points and the root system through the transparent walls of the flower container.

The best protection against any disease, including black rot, is strict observance of the requirements for placing a flower in a room and proper care for it.

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Methods for treating orchids from black rot

First of all, a diseased plant with signs of black rot must be instantly isolated from all other orchids and carefully examined, assessing the situation and the possibility of salvation.

If the lesion is small, the flower is removed from the substrate, and all rotten areas are removed with disinfected tools to healthy tissue. Places of cuts are treated with antiseptics that do not contain alcohol or sprinkled with cinnamon or charcoal powder, covered with sulfur.

Leave for several hours to dry the wounds, then the plant is treated with a fungicide. Among the pathological microorganisms, Pythium ultimum is considered an extremely aggressive fungus. Not every fungicidal agent is suitable for its destruction.
It is preferable to choose strong drugs, for example, Propamocarb and others that contain the active ingredient metalaxyl-M and some copper compounds, for example, Bordeaux liquid.

When treating with a fungicidal preparation, you should be careful about the root system, carefully observe the dose of the drug, otherwise you can harm an already weakened plant. It is advisable to keep the roots in a fungicide solution immersed for no more than 10-15 minutes.

Window sills or racks where the diseased orchid was located should be thoroughly washed with a disinfectant. It is advisable not to reuse the container in which the rotted plant grew when planting orchids, otherwise, it is washed in high-temperature water or soaked for several hours in a highly concentrated cleaning agent.

It is important to adjust the content of all plants in the home orchid collection in accordance with all the necessary requirements. It is important to remember that it is mainly those flowers for which the conditions of placement in the house and the rules of care are violated. Any disease affects weakened plants with reduced immunity.

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For an orchid grower, such a serious disease as black rot on an orchid is always a test. What to do, how to treat, is there a chance to save the affected plant – such questions are overcome in the very first minutes of the symptoms of the disease detected. If you take urgent measures and do not miss the time, the flower can be cured and saved. Otherwise, the plant will only have to be disposed of.

I am an avid plant enthusiast and horticulture aficionado with a deep passion for houseplants. With years of nurturing green companions, my expertise in caring for indoor foliage is well-rooted. Through my journey, I've cultivated insights into optimal plant care, propagation techniques, and creating vibrant indoor ecosystems. Join me as we explore the verdant world of houseplants together. Let's turn your living space into a thriving oasis of botanical beauty. Connect with me on and Facebook and explore more at Houseplantspro. 🌿🪴

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