Virus diseases of caneberries
Viruses are submicroscopic pathogens that infect cells, changing some cell functions and causing disease. Several plant viruses can infect caneberries in California. These include Blackberry calico virus, Raspberry bushy dwarf virus, Raspberry leaf curl virus, Tobacco streak virus, and Tomato ringspot virus. Raspberry mosaic is the name of one of the symptoms caused by a complex of (group of several) plant viruses, not all of which have been identified.
Identification
There are generally no symptoms that are diagnostic for a particular virus. Symptoms of a particular virus can vary, for example according to the cultivar and virus combination. Unless the caneberries are tested by a plant diagnostic laboratory it can be difficult or not possible to know which of the multiple viruses that affect caneberries are causing the damage symptoms. Plants can be infected with more than one virus at the same time.
Blackberry calico virus. This virus causes jagged yellow blotches in leaves of blackberry and its hybrids. Fruit sometimes becomes misshapen. But yield amount or quality may not be significantly reduced by infection with this virus if the plants are appropriately irrigated and otherwise provided with good cultural care. The virus is acquired in the plant nursery during grafting or vegetative propagation of infected plants. It also spreads in the field even though no vectors of it are known.
Crumbly fruit. When drupelets do not stay together well, fruit can crumble or fall apart when picked or otherwise handled. Viruses that can cause crumbly fruit in certain varieties include Raspberry bushy dwarf virus, Raspberry leaf curl virus, and Tomato ringspot virus. There are also several nonviral causes of crumbly fruit.
Raspberry bushy dwarf virus. This virus causes infected caneberry plants to remain undersized and have spindly (thin) canes. Infected plants develop pale green, yellowish, or whitish bleached leaves. Affected shoots have shortened internodes that can give plants a witches' broom appearance. The virus is spread by pollen from infected caneberries.
Raspberry leaf curl virus. This pathogen causes leaves to become rounded and curled. Tissue between leaf veins arches upward. New canes are undersized and each year are shorter than the previous year. The canes are yellowish at emergence, but soon darken, become stiff and brittle, and frequently do not branch. As the disease progresses, canes will not bend to root at the tips. Symptoms often appear on a single cane during a growing season and may not spread to other canes until the following season. After a cane shows leaf symptoms, its fruit become crumbly. This virus is spread by certain aphids.
Raspberry mosaic. When several viruses infect caneberries, symptoms can include leaves with large, green blisters around which the tissue turns yellowish. Leaves remain abnormally small and may be deformed. Leaves that develop during hot weather show only faint symptoms or none at all. Progressive stunting of canes occurs with cane growth being shorter each growing season. The tips of young canes may bend, turn black, and die. Berries on severely affected canes are dry, seedy, or crumbly.
Tobacco streak virus. This virus generally causes no symptoms on canes or leaves and has a relatively weak effect on caneberries. However, infection by the virus can weaken plants and reduce the fruit quality. The virus affects both blackberries and raspberries and is spread by pollen from infected caneberries.
Life cycle
Caneberries can become infected with viruses during propagation. Some viruses are mechanically spread by tools used in the nursery or through grafting with an infected plant that may be symptomless. Certain viruses are transmitted by pollen from infected plants, insects such as aphids and thrips, and root-feeding nematodes. The insects and nematodes acquire the virus while feeding on an infected plant and introduce the pathogen(s) when they move to feed on other caneberries.
Damage
Viruses can cause a wide range of symptoms as detailed above. For example, affected leaves can become cupped, discolored, and undersized. Canes may be shorter than normal, spindly, and weak overall. Once symptoms of virus infection become obvious in a caneberry, the plants commonly become unproductive in 2 to 3 years, producing little or no fruit or fruit that is virtually unharvestable because it is crumbly.
Solutions
Before planting caneberries consider having soil tested for the presence of Xiphinema species of nematodes that are a vector of some of these viruses. If Xiphinema are present, consider not planting caneberries at that site.
Purchase and plant only high-quality, certified virus-free or virus-resistant nursery stock or seeds. Do not graft virus-infected plant parts onto virus-free plants because this will introduce the virus. Remove any wild caneberries growing near those grown for their fruit because wild caneberries can be a source of infection. Note that where host plants occur in riparian areas there are regulations that limit vegetation removal. Before managing vegetation along waterways, contact the California Department of Fish and Wildlife to learn of any rules that may apply to your situation.
Although certain viruses are spread by the feeding of aphids and thrips, controlling insects has generally not been shown to effectively prevent virus infection. No pesticides are recommended for virus management.
There is no cure or treatment for virus-infected plants in gardens and landscapes. Provide plants with a good growing environment and proper cultural care to make them more tolerant of pest damage. If the caneberries are not performing as desired, remove and replace them.
Adapted in part from Blackberry (Rubus spp.)-Virus Diseases, Pacific Northwest Plant Disease Management Handbook and Controlling Diseases of Raspberries and Blackberries, Diseases of Raspberries and Erect and Trailing Blackberries, and Viruses and Virus Diseases of Rubus (PDF), U.S. Department of Agriculture. |
Chlorotic and necrotic mottled and distorted leaves, symptoms of Raspberry mosaic due to infection by multiple viruses.
Yellowing of raspberry foliage due to Raspberry bushy dwarf virus.
Severely cupped, undersized leaves of olallieberry blackberry due to infection with Raspberry bushy dwarf virus.
Pale leaf mottling due to Tomato ringspot virus.
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