March 27, 2004

By Sandy Woods, Master Gardener

While I have been known to spend countless hours tending to my outside garden, there are relatively few indoor plants that have captured my interest.  African violets are among the few.  Hence, I was quite dismayed when I recently found one succumbing to a fuzzy gray mold.  After some research, I was able to discern that the most probable culprit was a fungus known as Botrytis, Botrytis blight, or gray mold.

Botrytis disease can affect many different vegetable, fruit, and ornamental plants.  Under favorable conditions of high moisture and cool temperatures, the Botrytis fungus produces massive quantities of tiny gray spores, which are readily blown or splashed onto healthy foliage.  Botrytis can be particularly damaging when rainy, drizzly weather continues over several days.

Botrytis is a weak pathogen that must have some food source (nutrients) in order to invade a plant.  Wounded plant parts and dying tissue such as old flower petals can provide such nutrients.  Upon invasion, dark to light brown rot forms in the wounded or dying tissue, and from this food base the fungus can become more aggressive and invade healthy tissue.  The first symptom is typically a water-soaked spot which later collapses.  If the humidity remains high, a grayish-brown fuzzy coating of fungal growth develops on the diseased tissue.  Botrytis can cause collapse of seedlings, blossom blight, fruit rot, stem or crown rot, and/or shoot blight. 

Control of this disease requires control of the environment.  Cultivation, and opening of plants by wider spacing of rows and plants, or by pruning, permit freer movement of air and help reduce humidity.  Indoors, good ventilation can help.  Overhead, insufficient, and excess watering should be avoided.  Chemical or mechanical injury, and improper fertilization should also be avoided.  Open flowers and petals should be kept dry.

Fungicide use is often unnecessary if careful cultural practices are followed.  If a fungicide is needed, select one labeled for Botrytis control on the plant/crop you are growing.  Fungicides provide the best control when applied before the fungus becomes a significant problem.  When using any kind of pesticide or chemical treatment, always apply as indicated on the product label, and follow other label directions carefully.

University of California Cooperative Extension Master Gardener Volunteers can provide additional gardening information upon request.  Call the San Luis Obispo office at 781-5939 on Mondays and Thursdays from 1 to 5 PM, the Arroyo Grande office at 473-7190 on Wednesdays from 9 AM to 1 PM, or the Paso Robles office at 237-3100 on Wednesdays from 9 AM to Noon.  The San Luis Obispo Master Gardener website is at  Questions can be e-mailed to