Blackberries are desirable for their tasty and abundant fruit. These hardy plants are native to the United States and can adapt to a wide range of soil (except extremely wet soil) and growing conditions. Some types of wild blackberries are such vigorous growers that they are considered to be invasive weeds. Blackberries can suffer from fungal diseases that attack all parts of the plant.
Cane blight is a fungal disease that attacks the wood of the blackberry plant. The fungus enters the canes through a wound such as those caused by pruning or a nick by a gardening tool or lawn mower. Symptoms appear late in the growing season as cankers (dark, cracked areas of wood). Canes that have cankers may wilt and produce poor quality fruit.
To prevent the disease from spreading, prune affected canes 6 inches below the canker. Dip the pruning tool in a 10 percent bleach solution between cuts. A systematic application of copper fungicide in early spring can help prevent the disease.
Botrytis blight is common during cool, wet springs and summers. This fungal disease spreads by rain and thrives in wet conditions. The spores of the fungus infect leaves and buds, covering them with a dull gray layer of fuzz and causing them to shrivel or curl up.
Once infected, you can try to control the disease by pruning any affected areas. Do not let infected foliage sit on the ground, as the fungus can invade and overwinter in the soil. Instead, throw away infected foliage or burn it. Afterward, treat the plant with a systemic fungicide to protect it from subsequent infections.
Postharvest Soft Rot
Postharvest soft rot is a fungal disease affecting the blackberry fruit after it has ripened, or if the fruit becomes damaged. The fungus covers the fruit with a layer of fuzzy growth,and causes the fruit to rot. Postharvest soft rot often affects blackberries that are improperly stored. Harvested berries should be kept in a cool location where air can circulate around them.
Orange rust is the most common fungal disease of blackberries, according to the University of Arkansas. The fungus lies dormant in the plant, rising in the spring to attack the brambles year after year. While orange rust disease is not usually fatal to a blackberry plant, it can greatly reduce fruit production. New growth is thin and malformed, and the leaves develop growths that are powdery-orange in color. Affected leaves drop from the plant.
A systemic fungicide treatment and plenty of air circulation can help prevent the disease, but already infected plants should be dug up and destroyed, including the roots.