Raspberry vines and plants come in a variety of cultivars, many of which are classified as "disease-resistant." However, even if you have a raspberry plant that is resistant to many forms of infection, it is still important to the success of your crop yield and volume that you be able to identify early signs of problematic diseases of raspberry plants in order to prevent plant death and destruction of fruit crops.
Anthracnose is a fungal infection that appears on raspberry canes in late spring. On raspberries, the disease is characterized by purplish, oval lesions. As these lesions grow, they girdle the canes, resulting in cane death and stunted fruit, if any appears. Later in the season you may spot new infections in the form of purple spots on leaves. Remove all affected foliage and dispose of it in a sealed plastic bag or by burning. Rake away all debris underneath the plant to prevent reinfection. In some areas, fungicides can be used to treat anthracnose, but check with a local professional since not all fungicides are legal for use on this type of infection certain areas. If the infection continues to return, remove the plant completely to limit the spread of the disease.
Gray mold causes both blossom and fruit rot. Gray mold is easy to spot as is creates a large, velvety mass that is the fungus's fruiting body. Use sterile pruning to remove all affected parts of the plant and rake away debris from beneath the plant to prevent reinfection. In most cases, this should control the infection but you will need to be careful to avoid bruising the fruit during harvest or your fruit may develop a second wave of the infection.
Raspberry mosaic virus is spread by aphids. It causes the leaves of the raspberry plant to become yellowed and mottled and, left unchecked, will create blisters on the plants. The results are stunted growth and poor yield, while existing fruits are crumbly and small. You will need to eradicate the aphid to control the disease. Aphids can be controlled naturally by treating plants with neem oil or with a dilution of mild, green soap and water. Nematodes can also be introduced to the soil to help control the aphid population, or a more conventional pesticide may be used.