Virus diseases are one of the most serious disorders affecting small fruit crops. Although viral disorders in these plants have existed for many years, our knowledge in this area did not come about until relatively recently. We now know plant viruses are parasites. Some viruses attack a wide assortment of different plants, while others are very specific as to the particular host plant. Viruses cannot be controlled by pesticide sprays, and once having entered a plant, there is virtually nothing that can be done to prevent or lessen the damage that will ultimately occur.
In small fruit crops, viruses are mainly transmitted by sucking insects, particularly aphids and leafhoppers. Nematodes, commonly found in soil, also transmit viruses to small fruit crops by piercing and damaging roots with their mouth parts. Grafting and budding of stock, for instance from virus-infected grapes to healthy grape plants, will likewise result in transmission of the disease. Of course, if plants such as blueberries and strawberries are infected with viruses, any cuttings or runners will be virus-infected.
Visible symptoms may be evident causing suspicion of infection by a virus. Indeed, the names of many viral diseases such as mosaic, stunt, false blossom, leaf curl, dwarf streak, and ringspot are derived from the common appearances of infected plants. Yet, some types of virus damage such as loss of vigor, decrease in fruit set, reduction in fruit quality, and change in the normal pattern of ripening are more subtle as far as the implication of viruses, and therefore, difficult to pinpoint. On the other hand, it should be recognized that many virus-like symptoms can be expressed by plants as a result of factors such as insect and mite damage, unfavorable weather, nutrient imbalance, air pollution, and herbicide spray damage.
Control is primarily based on prevention of virus infection. The first line of control begins by purchasing high-quality, “registered” or “certified” plant material. These terms generally mean that the nurseries are producing plants free of any viruses. The second line of control is focused on aphids and leafhoppers. This can be effectively done by adhering to a routine insecticide spraying schedule.
Controlling nematodes in the soil can be accomplished by rotation of new plantings, as is commonly recommended in the case of strawberries. This practice effectively eliminates the host plants for a period sufficient to starve out the pests. In addition, eliminating weeds on which many nematodes also feed may be helpful in reducing nematode-transmitted viruses in the soil.
If your plants begin to show symptoms which suggest disease or infection, it is wise to have a diagnosis made. Local Extension offices supply the various forms, fee amounts if applicable, and procedures required for submitting plant samples for diagnoses. Should the samples be diagnosed as virus-infected, the plants must be dug and destroyed as soon as possible to prevent transmission of the disease to healthy plants.
As the old saying goes – an ounce of prevention is worth a pound of cure. Taking precautions that reduce the incidence of viral infections in small fruit plantings will result in bountiful harvests for years to come.