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Most Common Orchid Diseases and Pests

 
By Ulla Rothschuh Osorio, Biologist. January 16, 2024
Most Common Orchid Diseases and Pests

Orchids are popular indoor plants for their delicate beauty. Such aesthetic delicacy does not mean they are naturally less resistant than other flowering plants if they are given the right care. This is often the problem with orchids as they require specific care and environmental conditions to thrive. If they do not receive this care, they can develop various problems which threaten their health and can even lead to death of the plant. Some of the most common diseases and plants in orchids include root rot, brown spots on leaves, fusariosis and other fungal infections, among others.

In this thedailyECO article, we look at the 7 most common orchid diseases and pests. We also explain what treatment options might be available for each one and the best ways to prevent them developing in the first place.

You may also be interested in: Cattleya Orchid Care for Indoors and Outdoors

Root rot in orchids

Since orchids are epiphytic plants, they can have roots which are green due to the presence of chlorophyll. In their natural habitat, they use these roots to attach themselves to trees. They do not require the same soil as many other flowering plants which use universal soil types. Their substrate is much looser and their roots act differently. The latter have a thing coating called velamen which absorbs moisture from the environment.

If the roots of your orchids have turned brown, it means the plant is sick. We might observe them being yellow or crumbling to the touch. The cause of brown roots is usually excessive watering. To resolve the problem, you will have to change out the substrate.

When changing the substrate of an orchid with brown roots, you will need to ensure the new one is lighter and less compacted. This will help to promote the passage of air around the roots. It will also help to avoid fungal infection since mold contributes to root rot in orchids.

Another factor you will need to consider when changing the substrate is removal of damaged roots (depicted in photo below). Removing any roots that are in poor condition will help return the others to better health. Make cuts with pruning shears that are clean and disinfected.

You can learn more about the substrate used for orchids with our article on caring for cattleya orchids.

Most Common Orchid Diseases and Pests - Root rot in orchids

Brown spots on orchids

When the green leaves of orchids have circular brown spots and an unpleasant odor, it is due to the proliferation of bacteria in the genus Erwinia spp. These bacteria spread quite quickly, something enhanced by the particularly humid conditions orchids require to thrive. This bacteria can kill the plant in only a few days, so it should be treated immediately.

Leaves with spots should be cut down to the points they are affected. This should also be down with sterilized tools to prevent the spread of infection. Learn more about similar diseases and pests in orchids with our article on causes of black spots on plant leaves.

Fusariosis

This disease is caused by a fungus of the genus Fusarium spp. which attacks the plant's vascular system. When this orchid disease occurs, it prevents the passage of water and nutrients. It is detected because it causes yellow spots on the plant. When cutting the leaf where it is damaged, there are also purple spots inside. It is difficult to treat this disease, so prevention is best. To do so, avoid overwatering and have a container with sufficient drainage.

To treat this plant fungus, you can get a fungicide such as thiophanate methyl as shown in the photo below. The instructions for use that appear on the label of the marketed product must be followed.

Most Common Orchid Diseases and Pests - Fusariosis

Botrytis fungal infection

This is another fungal infection in orchids, this time caused by fungi of the genus Botrytis. It can be seen specifically in flowers that have already opened their buds and that have light-colored blooms such as white, yellow or green.

The fungal infection manifests itself as black or brown dots on the plant. As in the case of fusariosis, the best thing to avoid this fungal disease is to take care to carefully control its water content. As a treatment, the flowers should be removed to decrease the source of infection and a suitable fungicide should be used.

Learn more about fungal infections in plants with our article on why a plant's leaves are turning yellow.

Rust infection

This is another type of fungal infection in orchids. Many diseases in orchids are caused by fungi, but we are often able to diagnose them by the color they present on the leaves and flowers. Orchid rust is caused by fungi of the genus Puccinia. This cause a reddish-orange growth to develop on the plant which appears like rust on metal, hence its name. However, it can also look reddish purple, as is the case with Puccinia phragmitis shown in the photo below.

When this fungal orchid disease occurs, we should start by separating any affected plants from healthy ones. This is because of the potential spread of the fungal spores. As a direct treatment, the infected leaves should be cut at the end to remove any diseased parts. As a preventive measure, irrigation, substrate and ventilation conditions must be improved so that there is no further risk.

Most Common Orchid Diseases and Pests - Rust infection

Red or purple orchid leaves

Sometimes orchids may have leaves that have turned a red or purple color. This is not due to an orchid disease, but it is likely a sign it has been receiving too much sun. Wild orchids grow in the shade of trees, so they do not usually tolerate direct sunlight well. When they do receive too much sun, the leaves begin to produce these pigments to defend themselves from the UV rays as a form of sunscreen. Doing so causes stress on the plant.

To remedy this, the orchid in question should be moved to a location where it receives less light. Remember that they grow very well under domes, near a window or in indirect light.

Pests on orchids

We have discussed the various diseases which can affect orchids, but we have yet to mention pests. The following are some of the most common pests which affect varies species of orchid:

  • Aphids: one of the most common orchid pests, aphids are small insects which suck sap from various plants for sustenance. Although most common in temperate climates, they appear almost worldwide.

  • Spider mites: they are not a type of spider, but another arachnid animal that particularly like hot and dry conditions. If we keep our orchid nicely humid, it should help avoid spider mite infestations.

  • Whiteflies: another insect that feeds on the sap of plants. There are thousands of individual species which can be of various colors, although they usually have white on them.

  • Snails and slugs: these orchid pests are mollusks that will eat vegetation of many different plants. This includes orchids. They are easier to control if you keep your orchids indoors.

  • Mealybugs: a type of white scale insect that produces a cotton appearance on the leaves and stems. In addition to mealy bugs, there are many different types of scale insects which can damage these plants.

We should be vigilant to check all parts of the orchids since infestations can be localized to the underside of leaves. This is the case with aphids and spider mites since they tend to prefer to hide from potential predators.

It is possible pests are acquired by contagion from another plant, by excess humidity or by too much nitrogen-rich fertilizer. To eliminate pests, biological control can be used. This means introducing a species which feeds o the pest. However, we need to be careful they too won't damage the aphid in the process.

If this is not possible, you can use insecticides which are usually sprayed directly onto affect areas. We should use natural products as far as possible. Alcohol can also be sprayed with effects similar to insecticide in some cases. Stop these treatments when the aphids disappear, so as not to affect the plant.

Now you know about the most common diseases and pests that can affect orchids, you may want to learn more about these beautiful plants with our article on the rarest orchids in the world.

If you want to read similar articles to Most Common Orchid Diseases and Pests, we recommend you visit our Plant care and cultivation category.

Bibliography
  • Freuler, M.J. (2008). Orchids. Argentina: Albatross.

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