BANANA BUNCHY TOP

Banana bunchy top is a viral disease caused by a single-stranded DNA virus called the Banana Bunchy Top Virus (BBTV). It was first identified in Fiji in 1889, and has spread around the world since then. Like many viruses, BBTV was named after the symptoms seen, where the infected plants are stunted and have "bunchy" leaves at the top. The disease is transmitted from plant-to-plant in tropical regions of the world by banana aphids, which can also feed on Heliconia and flowering ginger (from the Zingiberaceae family), which is an important factor in control of the disease. There are no resistant varieties, so controlling the spread by vectors and plant materials are the only management methods. Symptoms include spotting any deformed plant appearance.   

With fewer banana plantations in the Bunchy Top infection regions, we can really step up the effort to find every last infected plant as soon as possible before aphids can spread the disease.

Importantly, we know Bunchy Top exists in home gardens so we need your help in our quest to completely eradicate this disease.

What does BBTV look like?

In its early stages the symptoms are difficult to see to the untrained eye. The first symptom is short dark dot-dash lines appearing along the veins of the youngest leaf starting from the mid-rib.

Symptoms include dark striping on leaf mid-ribs

You can see these dot-dash lines best when you look upwards towards the sky through the bottom side of the youngest leaf.Dark green stripes running along the mid-rib of the infected leaf may also be present. When the disease is more advanced, each new leaf becomes shorter, narrower and stands more upright, giving a ‘bunched’ leaf appearance – that’s why it is called ‘Bunchy Top’.

Plant growth is stunted and the leaves roll slightly upwards and tend to become yellow or light green (see picutre of an infected plant, above right).

Bunchy Top is difficult to identify in its early stages in any banana variety, including Cavendish and Lady Fingers, so trained professional inspectors should be called to find infected plants early before the disease spreads any further.

How is it spread?

Bunchy Top can only be spread in two ways:

Aphids on an infected plant

1. Banana aphids

The aphid is a small black insect which looks similar to other aphids you see in your garden.

The difference is that the banana aphid spreads Bunchy Top after it has fed for many hours on an infected plant. Aphids can by carried many kilometres on the wind so they can progressively infect many banana plantations and backyard plants.

2. By infected planting material

The biggest problem is that well meaning people give away young plants or suckers to neighbours and friends.

How does it affect plants?

New leaves look “bunched”

Banana plants infected with Bunchy Top will produce only small bunches, or no bunches at all.

The plants cannot recover from the disease and new suckers will also be infected.

Bunchy Top gets its name because the disease causes new leaves to become shorter, narrower and to stand more upright giving a “bunched” leaf appearance. This makes it difficult for the plant to produce a bunch.

Management

There are no resistant varieties of banana against BBTV, so the most common method of control is chemical control of the aphid vectors. Another way to help control the virus is to remove and destroy any infected plants before the virus can spread, which is a practice known as rogueing. Quarantines are also implemented to prevent the import of any potentially infected plant materials, including one in Hawaii that prevents the movement of fruits from the island of Oahu to any other island, since BBTV is widespread in Oahu. Fruit is not often produced on infected plants, but if it is, the fruit will be deformed, which easily identifies if there is any virus present in the fruits to comply with quarantine regulations. Since bananas are not the only host, the alternate hosts for both the virus and the aphid must also be monitored for disease, and sprayed with pesticides to control the aphids more. When planting at the beginning of the season, the seed material or suckers should be obtained from BBTV free areas of the world or from cultures that are grown and developed to be free of the virus.Currently, there is ongoing research into biopriming, or inducing systemic resistance by using bacteria that live inside the host but do not infect.

Control of banana bunchy top is achieved by killing the banana aphids then destroying all infected material. First, the aphids should be killed on the infected banana material, and then all the plant material should be destroyed to prevent the spread of the virus. Infected banana plants can be sprayed with an insecticide like Sevin to reduce or get rid of the aphid population, since control of viruses starts with control of the vectors.The agriculture department, however, recently obtained an EPA waiver for the pesticideProvado is a means of controlling the aphids that spread the disease.