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As with all plants also applies to orchids: a good care is the best prevention. But despite optimally coordinated supply of nutrients, water and light, it can lead to diseases and pests on your orchids. In the following sections, we will introduce you to the most common and explain what you can do about it.
The mosaic virus shows on older leaves by black, mosaic-shaped spots on the underside of the leaf, which spread in the later course of the disease on the upper leaf surface. Then the stalks of the orchids rot from the inside out. If you find an infestation, you should immediately dispose of the affected plants in your household waste, because a successful treatment of the viral disease is unfortunately not possible. To ensure that unrecognized infections do not spread to other orchids, you should thoroughly clean their scissors and knives before and after each use.
Phytophthora and Pythium fungi are responsible for the so-called black rot - also called root rot or Umfallkrankheit. The affected orchids turn yellow, turn black and ultimately die. In the genera Vanda and Phalaenopsis one notes a rapid leaf fall. Sick plants, infected pots or contaminated substrate are causes for the rapid spread of the fungi. Check your stocks regularly for abnormalities. Even cool and wet living conditions promote the spread. These two root infections are also incurable - so it's better to get rid of infected plants in a timely manner. However, the infections do not easily affect healthy specimens such as viral pathogens, which are often transmitted by sucking pests such as spider mites.
Leaf spot diseases
Occasionally occur on orchids also leaf spot diseases. They are caused by mushrooms of the genera Colletotrichum and Cercospora. The fungi cause yellowish, brown, black or reddish leaf spots, often with a dark border. Since they are weakness parasites, a suitable location and the proper care of your orchids are the ideal prevention. Infected plants can usually be saved by removing the affected leaves. Then place the orchids on the patio and treat them with a suitable fungicide.
Attention likelihood of confusion: Even burns, caused by a too sunny location, improper use of fertilizers or a lack of nutrients can cause yellowish and dark leaf spots. Therefore, first check whether the leaf spots are possibly of non-parasitic origin.
Among the most common pests on orchids are spider mites. The animals are mainly on the leaf underside of the affected plants. An indication of spider mites on orchids are bright speckled leaves that turn brown and dry later in the infestation.
Damage of the orchid spider mite (Tenuipalpus pacificus)
During the sucking action the animals inject a poison into the leaves, which strongly affects the growth. In addition, viruses, bacteria and fungi can easily penetrate through the puncture site. Remove all affected leaves. The use of predatory mites has proven useful in spasm against spider mites. With commercially available biological preparations based on potash soap or rapeseed oil, spider mites can also be combated well. However, always test the remedies first on one leaf, because not every type of orchid tolerates the treatment.
Since scale insects are usually introduced by newly purchased orchids, you should take a closer look at the desired plants already in the nursery.
The pests are found mainly on the undersides of the orchids, because there they are color adapted to their environment. The small scale insects feed on the sap of the orchids with the help of their suction pipe. The result: The leaves of the plants begin to deform and wither. The sucking action on the plant also creates small holes that are ideal entry ports for fungi and viruses such as the mosaic virus. The animals also glue the leaves to their excrement, the sugary so-called honeydew, on which a black mushroom turf often forms.
In order to avoid spreading to other plants, the first measure should be the isolation of the infested orchids. Once this is done, it is most effective to scrape off the scale insects with a knife and then collect them. Since scale insects hide between the bracts of orchids, it is advisable to remove them.
The biological control measure is the use of tea tree oil. The oil is ideally dabbed with a cotton swab on the affected parts of plants. The oil removes the breath from the pests and they die. But beware: with repeated use, such preparations can cause leaf shedding of sensitive plants.
Damage pattern of the fringed wing, commonly known as thrips
Thrips also damage orchids by sucking. They pierce the tissue of the leaf surface, filling the cells with air. These then reflect the light like little mirrors. This leads to a typical silver shine on the affected parts of the plant. Also black Kotreste indicate an infestation with thrips. As with spider mites, organic remedies with potash soap or rapeseed oil can help.