Pests and Diseases: Gray Mold (Botrytis cinerea)


Today we will be discussing a fungal disease known as Gray Mold or Botrytis cinerea. I’ve always called it by its latin name, Botrytis (pronounced BO-TRY-TIS), so forgive me if I go latin through most of this post. Botrytis is a fungal disease that can infect just about any crop, although herbaceous plants like perennials and annuals seem to be the preferred choices. Many people think of botrytis as a greenhouse problem, and while it certainly can be, it can also affect your outdoor plants.

It is often found on plant material that has been killed by frost but hasn’t been removed from the landscape. The plant that sticks out in my mind is balloon flower, or Platycodon. At the nursery that I used to work at, we would lose Platycodon by the hundreds if we didn’t remove the foliage soon after the first killing frost. Once the foliage is dead, it tends to accumulate moisture and that moisture breeds botrytis which infects the crown and ultimately kills the plants.


If you see a fuzzy gray mold on your plants when the weather conditions have been cool, cloudy and damp, chances are that you have botrytis. If the infestation isn’t particularly bad, you can remove the infected foliage (I don’t recommend composting it; I would trash it instead) and your plants should be OK come spring. I prefer to take a wait and see approach instead of going through the trouble of worrying myself whether the plants will survive. In the case of Platycodon, they are pretty prolific self seeders so you should have little babies that you can transplant to fill in any holes.


Peonies are probably the most well known as they are prized for their large flowers that appear in the spring. Unfortunately, botrytis can attack the buds before they open and lead to a display of black buds instead of beautful flowers. If your stems turn black from the bud down, botrytis is probably the culprit.

If you are a fan of Forget-Me-Nots, or Myosotis palustris, you may find that the centers of your plants open up and when you peek inside, there’s a colony of gray mold that has taken over…if that’s the case, you can bet that it’s botrytis.

Many, many other ornamental plants are susceptible to Botrytis including petunia, cyclamen, chrysanthemums and annual geraniums. Fortunately for the gardener, most of these disease problems occur in the greenhouse industry where plants are grown at intense densities.


Botrytis is spread by splashing water so it is imperative that the foliage has a chance to dry before the coolest part of the day occurs. In an outdoor setting, it is unlikely that you will have to water your plants when the cool, cloudy, damp conditions exist, but on the off chance that you do, be sure to water in the morning.

Sanitation is by far the best way to prevent your plants from becoming infected with botrytis. In the fall, remove foliage that has been killed by the frost and give your plants enough room so that air can get in to dry the foliage in the spring. Once the weather decides to stay warm, botrytis will be a thing of the past. Let me know if you have had problems with botrytis in the past and what you have done to remedy the situation. Leave me a comment below or e-mail me at Happy gardening!


January 3, 2012Permalink 1 Comment