Grey rot on a strawberry
Grey rot on the leaves of a rose bush
Grey rot on a tree (fig branch)
Grey rot on a rose
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Grey rot: how to prevent and treat botrytis
When uninvited, gray mold ravages ornamental plants, fruits and vegetables.
But on vines, under controlled conditions, botrytis can transform into noble rot (Botrytis cinerea). Winegrowers use it to increase the sugar content of grapes and wine.
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Gray mold is a fungal disease. It is a fungus, like rust and downy mildew, that grows on dead or decaying organic matter. There are several strains of botrytis, but they all work in the same way and cause the same damage.
Grey rot spares no crop. It affects fruit and vegetables in the vegetable garden (tomatoes, strawberries, peas, beans, etc.), and flowers in the garden (roses, lilies, peonies, dahlias, chrysanthemums, etc.). Some houseplants, such as Cambria Nelly Isler orchids, can also be infected.
Contributing factors
Botrytis likes humidity and temperatures between 17 and 23°. Outdoors, it is particularly active between May and September. In greenhouses, it rages as early as March.
Diseases such as powdery mildew favour the appearance of the fungus. It settles on damaged fruit and leaves. Finally, certain insects, such as budworms, provide an entry point when attacking plants.
How it works
In autumn and winter, the fungus maintains itself in the form of mycelium and sclerotia. When climatic conditions are favorable, it infects various plants.
Botrytis spores are spread by wind, rain, tools and gardeners' hands. They also survive in the soil or on dead plants. This volatility and resistance make the threat difficult to eradicate.
Gray mold attacks the aerial parts of plants. It takes advantage of a lesion, caused for example by an insect or a tool, to penetrate the plant.
Symptoms
Gray mold leaves cream-colored spots on the leaves, which turn brown over time. Infested by the fungus, the leaf blades rot and dry out. If nothing is done, botrytis spreads to stems and roots. The same stigmas are found on the stems as on the leaves.
Botrytis covers fruit and vegetables with a brown, then gray, felt-like film. Crops become soft and rot.
Flowers infected by botrytis are often at the end of their blooming period. They turn brown and wilt. The disease then contaminates the rest of the plant.
Treatment
Botrytis is complicated to exterminate. Prevention is the best way to protect your crops.
To avoid it, aeration is recommended. You must :
- prune shrubs to prevent twig entanglement;
- space out crops in greenhouses and vegetable gardens;
- ventilate greenhouses and indoor plant rooms.
Grey rot remains dormant in decomposing plants. To prevent it, remove weeds when you work the soil. And don't leave cutting waste or dead plants near your plants.
If you find that one or more of your specimens are affected, remove the affected parts and diseased plants.
You can also spray with Bordeaux mixture or a decoction of garlic or horsetail. Fungicides are also effective, but it's best to use them sparingly: the fungus is evolving, and chemical-resistant varieties of botrytis are now being observed.
