All plant lovers have succumbed at one time or another to the charm of orchids. It is impossible to resist their colours, the enigmatic shapes of their flowers and the immense variety of species. The problem is that for many it becomes a practically disposable or one-season plant, because they inevitably end up perishing, victims of some pest or disease. Hence the idea that it is a capricious or difficult to care for plant, when the truth is that with a little care you can keep it perfect for a long time.
The key to keeping orchids radiant and full of flowers is to prevent any disease or pest, and if it does become contagious, to be able to identify it in time and combat it quickly. To help you lose your fear of orchids, we have created this guide to orchid diseases and pests, how to identify and combat them.
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Diseases in orchids: learn how to identify them
Orchids are plants of tropical origin, with very specific requirements in terms of humidity, temperature and watering. If these parameters are not respected, then the plant will be an easy target for diseases and pests. It is important to check your plants regularly, be aware of any changes in the colouring of the leaves, flowers and roots and take immediate action if necessary.
Fungi
Fungi are one of the most common orchid diseases and this is no coincidence. Coming from tropical locations, orchids require a lot of humidity but this does not mean that they should be kept in very warm temperatures. When you put these two variables together, excess humidity and very high temperatures, then it becomes the perfect habitat for fungi. How to identify them depends on the type of fungus. The most common ones on orchids are:
Root, stem and pseudo-bulb rot - Rhizoctonia solani
This disease is very serious and it is not always possible to rescue the plant. The fungi produce spores that travel from plant to plant, so it is essential to isolate the diseased plant. It usually occurs because the plant is over-watered or because the substrate is not well drained. This causes the fungus Rhizoctonia solani to develop.
How to identify it:
Roots and leaves turn brown, lose consistency. Leaves may also turn yellow, wrinkle and fall off. On catleyas, older bulbs are affected first, turning brown and rotting.
How to combat it:
- Remove the affected roots with scissors that have been disinfected and sterilised.
- Apply an organic fungicide to the roots
- Transplant, changing the substrate and pot for new ones, which have adequate aeration.
- Avoid watering until the roots lose excess moisture.
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Fusarium Wilt - The Orchid Killer Fungus
This fungus invades roots and the cuts made in rhizomes when dividing plants. It is responsible for blocking the moisture that travels through the plant's vascular system. In Catleyas it is often caused by the use of contaminated tools, which spread the virus spores. In Phalaenopsis and Paphlopedilums it can be caused by a combination of factors such as a very cold and wet substrate with too much peat and too much salt.
How to identify it
In Catleya orchids it manifests itself in the leaves, which will look yellow, wrinkled and thin, but the definitive diagnosis is made by cutting off a rhizome. If you can see a discoloured circle in a purple or pink shade. If the infection is very severe and extensive, the entire rhizome turns purple, passes into the pseudobulbs and can kill the plant within 3 weeks. In Phalaenopsis orchids, damage starts at the root, which begins to rot and then spreads to the base of the plant. Younger leaves take on a reddish tinge, while older leaves look leathery. Leaves become blotchy, enlarging and creating yellow streaks. Flower stalks become blotchy and fall off prematurely.
How to combat it
- On Cattleyas, it is imperative to cut off and dispose of the rhizome and/or pseudo-bulb with the purple spots that denote infection. Use a fungicide on the cuts made. Remember to sterilise the scissors after each cut, even if it is on the same plant.
- In other species, it is necessary to discard plants with widespread infection. If it is just starting, you can cut off the infected parts and treat with fungicide.
- Isolate the silver while it recovers and always remember to disinfect cutting tools, best done with a flame.
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Black rot - Pythium and Phytophthora
This is one of the most devastating diseases. It is caused by two water spores, Pythium and Phytiphthora. It starts at the roots or at the base of the pseudo bulb and spreads rapidly, especially if the conditions that cause it to appear persist: too high humidity and temperature.
How to recognise it
Recognising black rot is simple, because you can see the black lesions, well delineated but with discolouration in the centre. In Cattleyas it starts with a little light yellow discolouration on one side of the pseudo bulbs. This will turn black and soft, then rot and fall off.
How to combat it
If your plant has fallen victim to black rot, the best thing to do is to cull it to prevent it from spreading, which it will do without problem through water droplets. Some people try to save the more valuable or exotic plants by cutting out the lesions and treating with a good fungicide, but this is not always effective and is risky.
Root rot - Rhizoctonia Solani
As the name suggests, this fungus rots the roots. It progresses slowly and is caused by rotting of the substrate, poor drainage or over-watering. This causes the roots to be damaged by the accumulation of salt, either because the irrigation water is too hard or because of over-fertilisation.
How to detect it
The damage caused by this fungus is the leaves turn yellow, shrivel and fall off. The pseudo bulbs turn brown, starting from the bottom upwards. Because it moves so slowly, it does not hinder the development of the plant, but this occurs slowly and the bulbs become yellow, shrivelled, thin and twisted. On Cattleyas, this fungus first takes over the older pseudo bulbs, turning them brown, and then advances to the younger ones.
How to combat it
- Remove the affected parts of the plant, sterilising the tool after each cut.
- Spray with an appropriate fungicide.
- Disinfect the growing space with bleach dissolved in water
- If the water in your area is very hard, you should wash the pots 3 or 4 times a year to prevent the accumulation of salts that can affect the roots.
Bacteria
Diseases caused by bacteria spread very quickly. The affected areas look soft, damp and gradually rot, leaving an unpleasant, almost stinking smell. There are 3 common types of bacterial diseases:
Soft rot - Erwinia spp
This bacterial disease is caused by two strains of erwinia spp. It appears when there are very high temperatures and excessive humidity.
How to recognise it:
Recognise the lesions appearing on the leaves of the plant, which spread rapidly in just a couple of days, covering the leaf and leaving it soft and sticky.
How to combat it
- If the lesion is small, cut it off with a sterile blade and put a little powdered sulphur or cinnamon powder over the exposed cut.
- Reduce moisture
Brown rot
This is also caused by another type of Erwinia sp and can affect the plant so violently that it kills it within a few days. It appears when the temperature is low and there is too much humidity.
How to recognise it
This bacterial disease of orchids is manifested by brown spots appearing on the leaves and pseudo bulbs of the plant. They look as if they are soaked with water, and these spots are surrounded by yellow halos.
How to combat it
The progression is so rapid that it is not recommended to treat it, but to discard the plant to avoid infecting other specimens. If you are feeling optimistic and the lesion is minimal, remove with a sharp, sterile tool, cover the wound with sulphur or cinnamon powder.
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Brown spot - Pseudomas sp.
Produced by the bacterium Pseudomas sp., this is a typical disease of Phalaenopsis orchids. If the lesion is allowed to progress to the top of the plant, it will most likely not survive. It is spread by water droplets but if you manage to detect it in time, it is easy to eradicate.
How to recognise it
It produces watery lesions on the orchid's leaves, which gradually turn brown. In their most advanced stage, these lesions exude a foul-smelling liquid.
How to combat it
Remove the affected parts using a sterilised tool. Spray with an antibacterial. Some people use hydrogen peroxide or bactericides with quaternary ammonium in their composition. Do not forget to treat nearby plants preventively.
Viruses
Viruses are not so common in orchids and are usually caused by external agents. From insects or pests, contagion by direct or indirect contact with infected plants, among others. There are more than 30 types of viruses that can attack your orchids, but it is almost impossible to eliminate them, so the safest thing to do is to get rid of the plant to prevent them from spreading, hopefully by burning it. If you touch a plant with a virus, disinfect your hands thoroughly or use disposable gloves.
How to identify them
It can be tricky to identify viruses in orchids, but the vast majority cause lesions or spots on the leaves that are repetitive, creating more or less defined patterns.
Most common orchid pests
Aphids
Aphids are among the most common and annoying pests. They are small insects, which can be black, green, brown or translucent in colour. They feed on plant sap and excrete a sticky honeydew that also attracts ants, creating a symbiotic relationship between the two insects. Aphids can transmit viruses, and also create conditions for fungal growth.
How to identify them
You can see the small insects on the plant, near the flower and the spike, but you can also see the leaves yellowing, drying up and falling off.
How to fight them
I usually use a solution of potassium soap or diatomaceous earth, both of which are environmentally friendly and do not harm the plant. Avoid watering the flowers. You can also buy yellow sticky traps, which attract and trap them.
Mealybugs
They are transmitted from plant to plant, so it is important to isolate new plants until you are sure they are healthy. They can also float in air currents if plants are indoors. Although they do not cause deep and rapid damage to the plant, they do affect the plant's appearance and growth, and can transmit viruses.
How to identify them
On the stems and leaves you will see small white or light yellow dots. If you look closely, you will see that they look a bit hairy, as the name suggests.
How to combat them
These insects are removed from plants by using commercial insecticides, although you can also use potassium soap or diatomaceous earth. You will have to apply several times to eradicate them, as they tend to hide in the substrate or in plant crevices.
Thrips
Thrips feed by scraping the cells of the plant's leaves and flowers, sucking out the juices that are released. They are very small, but you must eliminate them because they are vectors for the transmission of fungi, bacteria and viruses.
How to identify them
They leave silver-coloured marks on the leaves. You may need a magnifying glass to see them, because they are very small.
How to combat them
- Improve the ambient humidity, as a dry environment attracts them.
- Destroy infected flowers and leaves.
- Use simple commercial insecticides or potassium soap.
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