Botrytis
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.