Greenhouse growers and those who love soft fruits will likely be familiar with grey mold. This fungus is a subset of Botrytis cinerea and is very common. It’s marked by the grayish mold that grows on the infected plant.
Many common garden plants, both vegetable and ornamental, can be infected by this blight. Greenhouse growers will know it for its infection of everything from roses to tomatoes to soybeans. Soft fruit is especially vulnerable and gooseberries, strawberries and grapes are also often subjected to this fungus.
The most common symptom is the gray mold that usually coats the plant’s root stem at ground level and slightly upwards. It will be seen as gray spores and “fuzz” on the stems of fruit as well. It eventually manifests as “ghost spots” on fruits, leaving light rings of gray on their skins. Some fruit, such as berries, will literally be coated in it once thoroughly infected.
Like most Botrytis fungi, this one sprouts from spores and spreads quickly. It can infect a full grown tomato plant in a week or two and will spread through several means, including direct contact and short distances by “carrier” (bugs, birds, and human gardeners). Most commonly, it infects the soil and mulches that are left year-round, depositing thickly coated, almost seed-like spores that can overwinter and then come back to infect the next season’s crops.
How Botrytis Impacts the Plant
It can be anything from a nuisance to deadly, depending on how far it progresses and at what part of the growth cycle it gains a foothold on the host plant. Most infections will not kill the plant, but will severely limit its growth and development.
Wilted flowers, destroyed crops, and sickly, stunted plants are common.
How to Prevent Grey Mold
Like most fungi, prevention is the best way to keep this mold from getting out of hand and destroying your garden. Hygienic processes, especially under glass, is vital – remove all dead and dying leaves, buds and flowers promptly. Ventilation is another key, as is proper watering.
How to Treat
Several treatments are possible beyond destruction of the infected host. “Drought” treatments are common, wherein the gardener leaves the plant in full sun without water for three or four days to dry out the mold. This impacts the plant negatively, but does not destroy it in most cases.
Some natural and chemical fungicides may be tried with varying success.
Botrytis Grey Mold
Plant diseases: Botrytis or Gray Mold form Penn State Extension
Creative Commons photo courtesy of STEVENDEPOLO