Large Brown Spots on Phalaenopsis Leaves

Phaelanopsis are popular indoor orchids.

Phalaenopsis orchids are among the easiest orchid species to grow at home, but do need a little special care. Also called moth orchids, these plants naturally grow on the branches of trees, and require special soil-less orchid mix and some careful treatment. Like all plants, Phalaenopsis orchids may suffer from diseases and other problems, including brown-spotted foliage.

Diseases

A number of diseases, primarily fungal, cause brown spotting on orchid foliage. The spots usually start small, but can grow over time. A virus, called short orchid rabdovirus, may also cause disease-generated brown spotting on Phalaenopsis leaves.

Environmental

Some orchids develop brown spots from environmental conditions. These include nutritional imbalances, such as excessive zinc and manganese or too much iron, as well as temperature problems. Strong, direct sunlight can burn Phalaenopsis leaves, while temperatures below 50 degrees Fahrenheit can cause chilling injury, according to Purdue University.

Prevention/Solution

Treatment of brown spotting depends on the cause. Use regular fungicidal treatment against fungal spotting, and remove and destroy all affected leaves. Spotting caused by viruses is incurable, and requires destruction of the plant before the disease can spread. Treat sunburn by moving the plant to a shadier area. Chilling injury can't be treated after the fact. Avoid this problem by keeping plants in climate-controlled areas.

References

• Purdue University: Growing the Best Phalaenopsis
• University of Minnesota: Phalaenopsis and Paphiopedilum Species
• "Orchid Species Culture: Oncidium/Odontoglossum Alliance"; Margaret L. Baker, Charles O. Baker; 2006
• Brooklyn Orchids: Beginner Tips on How to grow Phalaenopsis Orchids