Virus diseases can seriously damage brambles, especially the raspberry, and can affect the lifetime of a planting. Once the plant is infected with the virus, the entire plant will be infected for the remainder of its life. Virus infections cause decreased productivity, so it is important to start a planting with healthy plant stock obtained from a reputable nursery.

Clean planting stock is usually obtained through meristem-tip culturing. Meristem-tip culture produces an essentially virus-free plant. These indexing methods vary with the type of virus to be detected. The virus-indexed plants are then used to propagate more plants to commercial quantities. For the plants to remain essentially disease free, they must not be increased in the field where viruses and other pathogens may infect the plant. These propagation methods also reduce the likelihood of other diseases such as crown gall.

Once the planting is established, viruses can be introduced into the planting by various means. The virus must be carried to the raspberry bushes by a vector. The three types of vectors responsible for spreading the viruses from plant to plant are aphids, nematodes, and pollen. The control of virus diseases is based on preventing the initial infection by removing sources of virus near the planting, mainly wild bramble bushes as well as the vectors. If a young planting shows virus symptoms, the planting stock was probably infected at the time of planting since symptoms do not usually appear the first season of infection.

general virus symptoms on leaves

Four major virus diseases are associated with brambles: mosaic, leaf curl, crumbly berry, and black raspberry streak.

Mosaic Virus Mosaic affects all raspberries but seldom affects blackberries. The mosaic virus complex overwinters in infected plants and is spread by aphids. Symptoms of raspberry mosaic vary with the raspberry variety, the type of virus infection, and the time of year. In general, symptoms may include delayed leafing out, dieback of shoot-tips, and stunted canes or clusters of shoots from the same node. Plants usually die in a few years. A mottling or yellowish spotting and cupping or blistering of the leaves are common symptoms most easily seen in the early spring when the new leaves are expanding. Leaf symptoms often disappear during hot weather later in the season. Red raspberries are not as severely affected as black but still suffer reduced plant vigor and yield. Care must be taken in diagnosis since these symptoms can be mimicked by late-spring frosts, powdery mildew, mite injury, fungicide and herbicide sprays, and boron deficiency.

Leaf Curl Virus Raspberries are more severely affected by leaf curl than blackberries. Many blackberry varieties, when infected, remain symptomless. Symptoms of infection by the leaf curl virus gave rise to the disease name. The leaves on infected canes are stiffly arched or curled downward. Leaves of red raspberry become yellow, while those of black raspberry take on a dark-green, greasy cast. Clusters of stunted lateral fruiting shoots arise from single nodes on the canes. The canes are stiff and brittle, and the fruit is small and crumbly. Symptoms on red raspberry are very mild or may not appear until the season after infection. This virus is spread by aphids and petiole grafting.

Crumbly Berry This is a red raspberry disease caused by the tomato ringspot virus and spread by the dagger nematode. Many plants which appear normal produce small fruit that fall apart when picked. This is a result of the failure of some of the drupelets in the berry to develop. This virus has a wide host range including many weeds such as dandelion. Symptoms of this disease vary with raspberry varieties and include yellow ringspots, which often disappear in mid summer on the expanding leaves of new shoots. The canes are sometimes stunted.

Control

Control measures are mainly aimed at removing sources of the virus particles from within and around the raspberry planting. Wild and neglected brambles should be destroyed within 600 to 1,000 feet of the planting. A good weed control program should be used to eliminate host plants for the viruses. Soil should be tested for dagger nematodes that vector viruses. Plants should be examined throughout the season for virus infection symptoms. If symptoms are detected, the plant must be removed. Strict aphid control should be maintained to prevent infection. These measures are all very important to the lifetime of a planting since, once infected with a virus, the plant will remain infected for life.