When cared for properly, Phalaenopsis orchids are hardy plants, however, they are still susceptible to diseases or pests.
The most common fungal diseases of Phalaenopsis (moth) orchids are Fusarium, Rhizoctonia, Pythium and Phytophthora. The symptoms are ambiguous, often not carrying particular signs but rather carrying many in common. For this reason, it’s a good idea to send in a sample of your orchid if it is infected with a fungus. If treatment is necessary, it’s best to go to your local nursery and ask what they have available for usage on orchids; products available can vary from retailer to retailer.
Bacterial infections in your Phalaenopsis Orchids are usually caused by poor sanitation. When growing orchids, or even trimming or transplanting them, use tools that have been sanitized by boiling them. Also make sure that your growing medium is sanitary. These things can carry bacteria to your plant, thus infecting it and causing its demise.
Insect infestations on your moth orchid can come in a wide variety. The most common insects to harm your orchid are mealy bugs (tiny bugs which can be found in flour), spider mites (they resemble spiders), scales, thrips, slugs, and snails.
These all feed on your moth orchid and will ultimately kill it. Sometimes even aphids can be a problem. To get rid of these pests, consult your local nursery to see if they have a pesticide gentle enough for your phalaenopsis orchid.