Bunchy Top Virus
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The virus can affect all plant parts at all growth stages. Initial symptoms can be mistaken for nutrient deficiency or physical stress and include the appearance of dark-green streaks on petioles, midribs and veins on the underside of new leaves. Later on, leaf laminae can also show these tiny dark green dots and dashes along the veins (called Morse code pattern). Affected leaves are stunted, slim and erect, and have curly and chlorotic margins that tend to turn necrotic. In advanced infections, new leaves show a worsening of these symptoms. The crown is characterized by the accumulation of small pale green or yellow leaves that form a "bunchy top. Overall growth is stunted and the plant may not produce bunches or fruits. If produced at all, fruits are deformed and small.
The symptoms are caused by a virus that is transmitted from tree to tree or between fields by the banana aphid (Pentalonia nigronervosa). Transmission over larger distances can occur via the carrying of infected planting material from one plantation to another. Further hosts of the virus include Ginger, Heliconia and Taro. Banana varieties differ in their susceptibility, the difference mainly shows in the time it takes for symptoms to appear. Plants do not recover from an infection. Primary infections through infected seedlings are generally worse than secondary infections via aphids. The symptoms are also exacerbated during the spring or during warm, dry weather.
If the disease is spotted at early stages, spraying the plants thoroughly with soapy water or insecticidal soap can help to reduce aphid populations. Control chemical usage so as to maintain presence of natural enemies of aphids.
Always consider an integrated approach with preventive measures together with biological treatments if available. There is no direct chemical treatment for viral diseases. Aphid populations can be controlled up to a certain degree with cypermethrin, acetamid, chlorpyrifos or related insecticides. In case of roguing plants in the field, treat them with power kerosene or insecticide to kill all aphids.