Also known as “gray mold,” this fungus infects a lot of herbaceous annuals and perennials. Botrytis has several species with the most common being Botrytis cinerea.
Many ornamentals including anemone, begonia, calendula, chrysanthemum, dahlia, fuchsia, geranium, hawthorn, heather, marigold, pansy, periwinkle, petunia, rose, and more. There are plant-specific blights which can infect peonies and tulips. For vegetable gardeners, there are botrytis blight infections known to affect asparagus, beans, carrots, celery, eggplant, grape, lettuce, onion, pepper, strawberry, tomato and others.
Symptoms of Grey Mold
Watch for silver-gray spores on plants growing in humid and relatively cool areas. If an area of a plant looks diseased or off-color, inspect closely for tiny specs that glint somewhat embedded in those areas – these are the sclerotia of the botrytis, which are like capsules for winter storage.
As the blight progresses, leaves and stems will show larger and larger spots from the botrytis as it spreads. It may also be present on crowns, flowers, buds, and can transfer through seeds and bulbs. It may manifest in different areas of the plant depending on species.
As with most fungi, this blight does well in damp or humid conditions with little air flow. It is a cool-weather fungus, however, so it thrives in lower temperatures (about 60F). It spreads relatively quickly and can go from plant-to-plant through irrigation, falling foliage, flying spores, by piggybacking on insects, etc. It often infects seeds or bulbs and overwinters with them.
How Grey Mold Impacts the Plant
Depending upon the host, the botrytis blight can be devastating or just a nuisance. In all cases, it will destroy foliage and lower fruit and flower production. It can sometimes kill the host plant and often does if it began with the host’s seed or seedling.
While botrytis mainly infects leaves and stems, it can infect every part of the plant except the roots, so it will often devour a small host plant in just a few days.
How to Prevent Botrytis Blight
As with most fungal infections, prevention is about managing the conditions in which the fungi thrive. Keeping the plants in an aerated environment, protecting them from over-moisture, and utilizing at-the-ground watering methods to keep foliage from getting too damp is imperative. Selecting seeds and seedlings that are disease-free and utilizing uncontaminated soils and tools is also important.
How to Treat Grey Mold
Treatment can be done quickly with sprays and fungicides. These are most effective when the blight is caught early. Removal of infected plants or plant parts through quarantine methods (using a bag, never touching other, clean plants, etc.) can also work, though it rarely gets all of the disease. Some natural remedies include bleaches, ammonia, and similar fungicidal chemicals.