Botrytis is a necrotrophic fungus that affects many plant species including orchids, mostly phalaenopsis, cattleya, cymbidium and dendrobium.

As the name suggest, it was firstly known from grapes, "Botrys" = "Grapes" in Greek; Botrytis = "The Grape Disease". The infection is caused by too much moisture, humidity and lack of air circulation.

It is a FACT: Botrytis spores are airborne and can be found almost everywhere. It is up to each individual grower to prevent them from establishing themselves in his place. A cool, moist environment with out any air circulation gives botrytis a good start. Given these ideal conditions the fungus can spread very quickly.

How do you know you have Botrytis? When you notice blemishes such as small black spots on the petals or on flowers, especially on white cattleya flowers. Older flowers are more susceptible. The smallish black or brown spots will grow larger and may merge if the infection progresses. The plant will not die. To my knowledge botrytis never killed a plant, but it will look sick and you will not enjoy the flowers.

Be aware, some “experts”, when they see the black spots, may tell you that you have a virus. Forgive them.

How to treat botrytis? When you notice botrytis, the first thing to do is increase the night temperature to over 20 degrees Celsius and provide good air circulation.

There are fungicides on the market and some can be used to eliminate botrytis. Cu-based fungicides are probably the best, but be aware that Cu-based products should not be used around the exposed roots of orchids. Cover the roots with a paper before you spray.

I use a product called “Rot Stop” (Not available in Australia) which is a natural disease control agent based on the active ingredient "Bacillus subtilis".

Pool Algaecides are also reasonable and can protect orchids from numerous pests and diseases. Pool Algaecides that contain "Benzalkonium Chloride" are reasonably good and do no harm the environment.