A wide variety of diseases can affect raspberry plants, including different kinds of blight, cane botrytis, anthracnose, leaf curl, mosaic disease, and vein chlorosis. Some of these raspberry diseases are caused by an invasive fungus, while others are viral in nature. Experts recommend purchasing plants that are certified to be free of viruses, due to the raspberry plant's particular susceptibility to viral diseases.
Many raspberry diseases originate with the presence of a fungus that negatively affect specific areas of the plant. In the case of cane blight, the fungus enters at the site of a wound in the branch that might have been caused by insect damage, pruning, or injury during transplanting. This disease is most commonly seen in black raspberries. Cane botrytis affects the plant's oldest leaves with brown spots or grayish streaks. In more advanced stages, the plant will develop dark blister-like sores. Anthracnose causes purple or red spots on the leaves, branches, stems, or fruit of the raspberry plant.
Spur blight, which affects the branches and leaves of the raspberry plant, typically begins as an infection at the leaf edges that spreads inward. This condition is more common on red raspberries and can prevent buds from flowering. Midge blight has a dual cause, as the disease-causing fungus is allowed entry into the plant by way of damaged tissue caused by midge larvae. It is one of the raspberry diseases that can cause structural damage to the plant. Leaf spot is evidenced by blackish green spots or holes in the plant's leaves, a condition that can be reduced with appropriate pruning or the use of a fungicide.
Some raspberry diseases are caused by a virus. Leaf curl manifests as a twisting and whitening of the raspberry plant's branches and leaves, with any fruit produced being extremely seedy and dry. This condition often occurs due to infection by wild raspberry patches. Mosaic disease is among many raspberry diseases that affect both the fruit and leaves as well as reducing the overall size of the plant. Vein chlorosis leads to the lightening and distortion of the raspberry leaf, as well as overall shortening of the plant.
To avoid or control raspberry diseases with a fungal origin, experts recommend maintaining plants with plenty of air circulation through adequate weeding and pruning. For plants that are watered through an irrigation system, avoiding long time periods of excessive moisture can help reduce fungal invasion. Fungicides can help with management of fungal diseases once they have appeared. A condition such as midge blight is more effectively addressed with an insecticide.