Blackberry plants are a species that has perennial roots with biennial canes that produce fruit the second year of growth. The second year, canes must be removed to allow for new cane growth each year. Blackberries are sensitive to wet conditions, as it creates an environment for plant problems and disease. Space blackberry planting rows 8 feet apart and prune the canes yearly to increase air circulation, which assists in keeping the plants dry.
Botrytis blight is a fungal disease that infects blackberry bushes when the outdoor temperature is approximately 60 degrees F, and the weather is cold and rainy. An infected bush will have gray-colored mold spores that are visible on dying and dead plant tissue. The fungus has the appearance of dust. Manage a botrytis infection by removing all infected branches and leaves; burn them to dispose. Apply a fungicide spray to the plants to protect against additional infections. Prevent a botrytis blight infection by pruning the plant to provide air circulation during wet periods, and watering the plant at ground level instead of spraying the entire plant.
Orange rust is a blackberry disease that is formed by a fungus that infects the brambles of the plant. The University of Arkansas Division of Agriculture lists an orange rust infection as the most common rust disease in blackberries. This type of rust infection is systemic, as it is capable of surviving inside the plant year after year. Orange rust does not kill the blackberry plant; instead, it weakens the structure and reduces fruit production. Symptoms of an orange rust infection are spindly, weak new shoot growth with pale, oddly-shaped leaves. The leaves form waxy pustules that turn powdery and orange in color; infected leaves fall from the canes in early summer. Remove and destroy infected blackberry plants, including the roots. Prevent orange rust infections by pruning healthy blackberry bushes to increase air circulation around the plants and applying a fungicide in the spring and fall seasons.
Crown gall is a soil-borne bacterial disease that enters a blackberry bush through pruning wounds in the plant, insect feeding holes or damaged areas resulting from wind and hail. The bacterium creates a gall at the point of infection, which will cause a decrease in growth, berry production and death in some plants. The gall appears as a rounded mass that has a rough surface and spongy texture that darkens as it ages. Prevent a crown gall infection by choosing disease-resistant blackberry varieties and planting in soil that has not been infected with the bacteria for a minimum of three years. Take caution when pruning blackberry canes to prevent excessive wounding of canes and sterilize all tools with rubbing alcohol prior to use. Remove and destroy blackberry canes and roots that are infected with crown gall to prevent the disease from spreading to other plants.