Gray mold, or botrytis fruit rot, is a fungal disease that commonly affects raspberry plants, as well as strawberries and blackberries. Most prevalent during rainy, cloudy weather, it can cause devastation to a berry crop. The symptoms can appear during the blossoming and fruiting stages, and even after the fruit is picked.
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Symptoms of Mold on Blossoms
Raspberry plants may start to show the signs of fungal infection in the flowering stage, with brown, dry areas on the blossoms. This "blasting" may appear on one or several of the flowers in a cluster, and also can extend down the flower stalks. Most of the infection occurs during this stage, although the full extent of the damage may not become apparent until the fruiting stage. It is important to recognize the signs at this early point.
Symptoms of Gray Mold on Growing Fruit
Once the infection is established in the blossom and the fruit begins to develop, it usually goes through a latent stage and is difficult to detect. Once the fruit begins to ripen, symptoms appear again. First light brown, soft areas appear on the berry and begin to spread rapidly. If allowed to stay on the vine, the raspberry becomes covered with a gray, fuzzy layer of mold. Eventually the fruit dries up and the mold becomes dusty and powdery.
Symptoms of Gray Mold on Picked Fruit
Picked fruit remains susceptible to gray mold. The same symptoms as above can develop after picking, especially if the fruit has been crushed or bruised. Handling infected fruit during picking also can spread the infection to healthy ones. Seemingly intact berries can rot within two days under the right conditions. Because the disease often goes undetected until harvest time, this is sometimes the first symptom that is noticed.
How to Prevent Gray Mold Symptoms
Plant raspberries in a site with good air circulation and drainage, and plenty of sun. Do not over-apply fertilizer, which can produce large areas of thick foliage that shades the fruit and prevents it from drying quickly. Place a layer of straw mulch around the plants, keep weeds under control, and plant rows along the direction of the prevailing wind so that the moving air will help to dry the fruit. Remove any infected berries from the plant and discard them in a different area.