Banana Streak Virus
The symptoms of the disease can vary widely, depending on the type and amount of virus involved, the plant variety and the environmental conditions. The most common symptom is the formation of even or broken yellow streaks that run from the leaf midrib to the margin. These streaks later turn brown or black and can be interrupted by yellow blotches or eye-shaped patterns. Necrosis starts to appear on the leaf, starting from the margin, and sometimes affecting midrib and petiole. Occasionally, the internal tissues of the stem are also affected by decay. The latter symptom is particularly visible under low temperature and short-day conditions. Not all leaves are affected but plant growth is usually stunted, while the size of the bunches and fruits is reduced.
The disease is caused by a complex of viruses. The nature of the symptoms is determined by the concentration of viral particles in plants. Temperatures, and weather patters in general, also influence the outcome of an infection. The virus is spread from tree to tree or between fields through several species of mealybugs (Pseudococcidae). Another means of long distance dissemination is the use of infected planting material or seeds. It is not soil-borne and unlikely to be transmitted via mechanical injuries to plants through during field work. It is a worldwide problem that affect banana and related species and that can adversely affect plant growth, fruit yield and quality. The virus is unlikely to be spread on cutting tools or by mechanical means.
Bio-control agents such as parasitoid wasps, lacewings or hover flies and lady birds can be used to control populations of mealybugs. Light mineral oils or neem extracts sprayed on leaves are also effective when populations are small.
Always consider an integrated approach with preventive measures together with biological treatments if available. There is no chemical treatment of viral diseases. The waxy protective coating of mealybugs makes them difficult to kill. Treatments with insecticides such as deltamethrin can be used to control mealybug populations.