Black Sigatoka

Alert

Black Sigatoka is a notifiable disease.

Under Queensland legislation, if you suspect the presence of this disease in any species of animal, you must report it to Biosecurity Queensland on 13 25 23 or contact the Emergency Disease Watch Hotline on 1800 675 888.

Black Sigatoka is a leaf spot disease of banana. It is an important banana disease in many countries around the world. Severely infected leaves can die, significantly reducing fruit yield, and causing mixed and premature ripening of fruit bunches. It is not present on mainland Australia.

Black Sigatoka is an important banana disease in many countries around the world. Severely infected leaves can die, significantly reducing fruit yield, and causing mixed and premature ripening of fruit bunches.

Movement restrictions from the far northern biosecurity zones 1 and 2 (PDF, 334KB) are in place to prevent black Sigatoka from spreading.

Cause

Black Sigatoka is a foliar disease of banana caused by the fungus Pseudocercospora fijiensis.

Other names

  • Black leaf streak (BLS)

Description

On leaves

  • Early leaf symptoms are tiny reddish-rusty brown flecks that are most evident on the underside of leaves.
  • These gradually lengthen, widen and darken to form reddish-brown leaf streaks.
  • The early streaks run parallel to the leaf veins and are more evident on the underside of the leaf.
  • The streaks broaden and become visible on both leaf surfaces.
  • The streaks expand and become more oval shaped and the centre of the lesion becomes sunken and turns grey over time. At this stage a yellow halo may develop around the edge of the lesion.
  • In susceptible banana cultivars, high levels of disease can cause large areas of the leaf to die, which can lead to total leaf collapse.
  • As leaves die, fruit yield is reduced and ripening of bunches can be uneven.

Plant stage and plant parts affected

Black Sigatoka affects banana leaves.

The unfurling and youngest fully expanded leaves on plants and suckers are the most susceptible to infection. The leaves become more resistant as they mature.

May be confused with

Mature leaf symptoms of black Sigatoka are similar to those caused by yellow Sigatoka (Pseudocercospora musae), a closely related fungus that is present in Australia. Early leaf spots of black Sigatoka are reddish to rusty-brown, and longer and broader than yellow Sigatoka. The spots are noticeable on the lower leaf surface.

In contrast, the early leaf spots of yellow Sigatoka are yellow-green leaf streaks that are narrower and shorter, and more prominent on the upper leaf surface than black Sigatoka. Both diseases can be present on the same plant.

Mature symptoms of Eumusae leaf spot (Pseudocercospora eumusae) are also very similar to those caused by both black Sigatoka and yellow Sigatoka. Eumusae leaf spot is not known to be present in Australia. Laboratory testing is required to reliably distinguish between these diseases.

If in doubt, always report suspect symptoms.

Distribution

Black Sigatoka is present in all major banana exporting countries.

The disease is widespread in South-East Asia, India, China, the southern Pacific islands, East and West Africa, USA (Hawaii), Grenada (Caribbean), Trinidad, and Central and South America. It also occurs in Papua New Guinea and on several islands in the Torres Strait.

Hosts

Susceptible varieties of bananas such as Cavendish and Lady Finger.

To prevent the spread and establishment of the disease, blak Sigatoka rcesistant banana varieties are the only bananas to be grown in the far northern biosecurity zones (PDF, 334KB). Refer to the Queensland biosecurity manual for further information (PDF, 1.8MB).

Life cycle

  • Black Sigatoka lesions can produce 2 spore types; conidia and ascospores.
  • The conidia are produced in the leaf streak stage, whereas ascospores are produced once the lesions become mature and have an obvious grey centre.
  • Water is required, either as rain or dew for conidia to be dislodged or ascospores to be released.
  • Both conidia and ascospores can then be dispersed by rain splash or by air currents.
  • Windborne ascospores are thought to be responsible for longer distance disease dispersal, whereas conidia are linked to spread within a plantation e.g. mature plants to suckers.
  • Once spores land on susceptible banana leaves, high relative humidity or the presence of water is required for their germination.
  • Depending on environmental factors and host susceptibility, development of disease symptoms can be as short as 27 days.
  • Black Sigatoka lesions can be present on all leaves on a banana plant, however new leaves (between emergence and unfurling) are most susceptible to infection.

Impacts

Bananas are a major horticultural crop with over 94% of the Australian crop produced in north Queensland. In 2016–17 the Australian banana industry was worth $600 million at the farm gate, producing 414,000 tonnes of bananas from approximately 13,000ha. There are 690 banana farms greater than 0.5ha in area, and in 2009–10 the industry employed 9,600 full time equivalent personnel, directly and indirectly (Source: Australian Banana Growers' Council).

Black Sigatoka can cause large areas of the leaf surface to die, compromising fruit size, quality (taste), and shelf life. In extreme cases fruit does not mature at all. Fruit loss varies from 30–50% depending on climatic conditions and the severity of the disease.

The number of fungicide applications required to control black Sigatoka (up to 55 applications per year in the Philippines and 60-70 fungicide applications per year in Costa Rica (Pattison, 2014) would result in significant increases in cost of production, should the disease become established in Australia.

The estimated economic damage of black Sigatoka establishing in Australia is around $60 million annually. This includes production losses to growers and the costs of eradication attempts shared by industry and government. The eradication of black Sigatoka from the Tully area in 2001–2005 cost $17 million (Cook et al., 2013).

Backyard plantings of banana are common in Queensland and would also be affected by black Sigatoka.

How it is spread

The greatest risk of disease spread is by people moving infected plant material such as banana suckers for plant propagation or banana leaves used for wrapping and packaging food.

Localised disease spread can occur from rain splash and wind borne spores, particularly during wet, humid, windy conditions. Tropical storm events could transport spores or infected leaf debris further afield.

Dead plant material can also pose a risk. Infected dead leaf material can continue to produce viable spores for months.

Spores of black Sigatoka can also be carried on banana packaging materials and equipment.

Monitoring and action

Inspect your banana plants regularly for the presence of unusual pest and disease symptoms.

For black Sigatoka look for the presence of streaks or leaf spots. The reddish to rusty-brown streaks are longer, broader and darker than the established and widespread yellow Sigatoka. Plants with advanced black Sigatoka disease may have large areas of dead leaf.

Report detections or suspect of black Sigatoka to Biosecurity Queensland immediately on 13 25 23.

Prevention

Banana plants propagated from tissue culture under the Quality Banana Approved Nursery (QBAN) Scheme are recommended as the preferred high health source of planting material to use. QBAN plants are now widely available for both commercial and backyard use.

The Banana Industry Biosecurity Guideline provides practical advice for banana growers on managing biosecurity risks (PDF, 433KB).

Protect your farm from plant pests and diseases:

Legal requirements

Black Sigatoka is restricted matter under the Biosecurity Act 2014. The disease has previously been detected on some northern (Boigu, Dauan and Saibai Islands) and eastern (Ugar, Erub and Mer Islands) Torres Strait Islands. Regulations are in place to prevent its spread.

If you suspect the presence of black Sigatoka on any other Torres Strait Islands, or on mainland Queensland, you must report it to Biosecurity Queensland on 13 25 23 or contact the Exotic Plant Pest Hotline on 1800 084 881.

By law, everyone has a general biosecurity obligation (GBO) to take all reasonable and practical steps to minimise the risk of spreading black Sigatoka.

The Far Northern Biosecurity Zones (PDF, 334KB) have been established to prevent the spread of far northern pests like black Sigatoka.

You cannot move Black Sigatoka and pest carriers such as banana plant material, or soil and other media and equipment or machinery (appliances) that has been in contact with banana plants, without a biosecurity instrument permit:

  • out of far northern biosecurity zone 1 into far northern biosecurity zone 2
  • out of either far northern biosecurity zones 1 or 2 into the rest of Queensland or Australia.

You must observe movement restrictions if you are travelling to or around the Cape York Peninsula, or if you live there.

For information about biosecurity instrument permits call the Customer Service Centre on 13 25 23 (from interstate use 07 3404 6999) or email qld.plantquarantine@daf.qld.gov.au.

Inspectors at the Cape York Biosecurity Centre at Coen check vehicles moving south, to ensure that all fruit, vegetables, plants, wood and soil are not moved from the zones, without a permit. Amnesty bins are provided after hours.

There are restrictions on planting bananas in the far northern biosecurity zones. Plants must be black Sigatoka resistant cultivars and planting is restricted to 10 banana plants or 30 banana pseudostems per property. There is also a requirement to remove any unwanted unmanaged plants.

These requirements are in place to reduce the risk of new outbreaks of black Sigatoka potentially infecting susceptible varieties, which occurred in the 1980–1990s.

Residents can apply for a biosecurity instrument permit to grow additional banana plants and new black Sigatoka resistant varieties.

Your cooperation in complying with these restrictions will help protect Queensland from black Sigatoka.

If you are unsure about the legal requirements, quarantine or movement restrictions, contact the Customer Service Centre on 13 25 23

Further information

  • Cook, D.C., Liu, S., Edwards, J., Villalta, O.N., Aurambout, J.P., Kriticos, D.J., and Drenthe, A. 2013. Predicted economic impact of black Sigatoka on the Australian banana industry. Crop Protection 51: 48-56.
  • Pattison, T. (2014). Changing times for global banana trade. Australian Bananas 41:36-37.