Gray mold, also referred to as Botrytis blight, is a fungal disease caused by Botrytis, a genus of fungus. Hundreds of plant species are vulnerable to gray mold, including common fruit-bearing plants such as strawberries, grapes, and apples, staple vegetables like onions and lettuce, and a variety of popular ornamentals. Plants infected with the disease feature symptoms including blotches, fungal growth, and rot on plant buds, flowers, fruits, leaves and stems.
Gray mold produces water-soaked spots and gray fungal growth—these symptoms eventually spread to other parts of the plant.
The first symptoms of gray mold typically appear on leaves in the form of water-soaked spots. These spots may or may not be white in color. These spots darken to brown or gray, and in humid conditions may produce the disease’s namesake gray fungal growth. When badly infected leaves are touched or picked, they will produce a cloud of spores.
Over time, the disease symptoms will spread elsewhere on the plant. Stems may develop cankers, and affected fruits develop flecked blemishes, and may succumb to rot. Seedlings and young plant shoots are particularly vulnerable to the ravages of the disease, often withering and dying. In severe cases, the entirety of a plant may become coated in fuzzy gray growth, and may also suffer from damping off and gummosis. Blossoms often fall victim to gray mold, resulting in reduced yields in fruiting plants.
Gray mold is caused by Botrytis, a genus of fungus found worldwide.
The fungus Botrytis is a pest which has afflicted growers for generations, and which cannot be escaped—it has been found on the island chains of Hawaii and the Canary Islands, and even on the continent of Antarctica.
Botrytis typically maintains a foothold in fields by overwintering in infected plant debris. When the weather is moist and cool, as is often the case in the spring planting season, conditions are ripe for Botrytis to infect vulnerable young plants. The fungus typically gains access to plants through wounds, broken stems, and damage resulting from spraying, fertilization, and mechanical equipment. Seedlings are also quite vulnerable to the fungus.
Controlling Botrytis requires controlling the growing environment, preventing the moist, cool conditions the fungus craves.
Preventative fungicides can be useful for stopping the growth of gray mold, especially prior to flowering, though some strains of Botrytis are known to become resistant to popular fungicides.
However, adopting proper sanitation practices is often more than enough to prevent and control the disease. Remove dying branches from plants and debris from the ground, and remove this material from the fields. Do not allow infected plant debris to remain on or adjacent to fields. Any badly infected plants should be culled from fields, as it is difficult to eliminate the fungus, and these plants will otherwise serve as disease vectors.
Avoid overhead watering, because water dripping and splashing off leaves readily spreads fungal spores to other plants. Instead, install irrigation hoses or comparable systems to water directly into the soil.
Ensure that plants are not planted too close together. Trim back lower branches to ensure adequate air circulation and increase direct sunlight to reduce humidity.
Lastly, avoid overuse of nitrogen fertilizers, as this deteriorates plant tissues. Weak plant tissues are easily invaded by Botrytis and other pathogens, and they readily succumb to infection. Instead, incorporate calcium into your nutritional regime, as this element is critical to hardy plant growth. Fusion 360 Integrity FG-Micros is another recommended addition, as it includes boron, another element which plants are often deficient in, but which is critical to the growth of ruggedized plant tissues that are resistant to injury and infection.