Common Orchid Diseases
Like most plants, orchids are vulnerable to many different diseases. Treatment ranges from simple brushing off to a whole routine of 'hospital' care.
Among the most common problems are viruses. There are over 25 reported viruses known to infect orchids, but there are probably many more. Two of the most common are the cymbidium mosaic virus and odontoglossum ringspot virus. In many cases, the plant will fight off any infection using its evolved mechanisms. But how effectively it can do that can be altered by the amount of sunlight, water and feeding provided to the plant.
Yellow or brown spots are a typical symptom, especially when they appear in rings. The petals may show brown streaks or discoloration. There are kits available that can help diagnose which virus is responsible and to treat it. In the interim, it's important to keep any infected plant isolated as some viruses can spread via air. Treatment may be as simple as an alcohol swab or dip, or a short soak in 10% bleach for a few seconds.
Isolation and quick treatment is essential. The injured parts should be cut off and the rest of the plant carefully inspected.
Fungi are another common problem when growing orchids.
Though orchids prefer a high humidity environment, it is possible to go overboard. That can promote the growth of fungi that are harmful. The risk is increased if the temperature drops too much at night. Keeping the environment above about 65F/18C will be helpful. Though, the number varies with different species. Some prefer cooler nighttime conditions, some warmer.
Gloeosporium is one of the more common types of troublesome fungus. It produces yellow spots that will eventually merge and evolve into a large brown spot. Simple air flow and mild drying can help cure the orchid.
Similar causes and treatments occur in the case of bacterial infections. Phytomonas cypripedii, for example, causes a brown rot. One way to lessen the problem is to ensure that tools and gloves are cleaned with bleach to prevent spreading by contact while working with the orchids.
Keeping any infected plant away from another is important. Trim any diseased portion you see and treat the rest right away. In some cases, it's best to know when to give up and simply try again. When you do replace a plant, be sure to carefully clean and disinfect any pot before reuse. That's easily accomplished with bleach, high heat in a microwave oven or other common method of killing disease-causing organisms.
