pests, diseases and disorders

Banana scab moth Nacoleia octasema

Posted on 2024-09-05 by Sarah Williams

Scab moth

The banana scab moth (Nacoleia octasema) is a significant threat to banana crops, with the potential to cause up to 100% damage to fruit if left uncontrolled. The larvae of this moth feed on emerging banana bunches, leading to cracking, scarring, and disfigurement of the fruit. Damage is usually confined to the outer curve of the fingers (the area nearest to the bunch stalk) but, in more severe cases, damage can extend to the stalk, areas between touching fingers, or even extend to cover the whole fruit surface. While the damage is usually superficial, severe cases can render the fruit unsuitable for the market.

Banana scab moth is present throughout the year but is favoured by moist and warm conditions, hence the greatest potential for damage is during the wet season.

Being proactive and regularly checking bunches or getting feedback from baggers can help growers discover infestations before the fruit reaches the packing shed. Although damage can’t be undone, identifying, and addressing problems (re-training or integrating alternative control options) sooner can save other bunches from impact.

To manage infestations, year-round treatment is essential, most growers use chemical control through bell injection is recommended to prevent banana scab moth damage. Proactive monitoring and management are essential to minimize the impact of this pest on banana crops.

More information

This information has been prepared as part of the National Banana Development and Extension Program (BA19004) which is funded by Hort Innovation, using the banana industry research and development levies and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture. The Queensland Government has also co-funded the project through the Department of Agriculture and Fisheries.

Banana scab moth – monitoring and control

Posted on 2024-08-23 by Sarah Williams

Banana scab moth – Nacoleia octasema

Monitoring and control options

Monitoring

Being proactive and regularly checking bunches or getting feedback from baggers can help growers discover infestations before the fruit reaches the packing shed. Although damage can’t be undone, identifying, and addressing problems (retraining or integrating alternative control options) sooner can save other bunches from impact.

The method for monitoring for banana scab moth is to inspect freshly emerged bunches (bract fall) for the presence of damage and/or larvae. Pay attention to the underside of the fingers in each hand (closest to the bunch stalk) and the cushion area. In very young bunches, lifting the developing hand away from the bunch stalk may be necessary to reveal any larvae and/or fresh damage.

Also, examine the base of the bunch stalk where the larvae enter the throat of the plant. Larvae can be detected by separating the base of the flag leaf and removing the bract that is attached to the stalk. Often a clear jelly-like substance or frass feeding waste, which appears to be associated only with banana scab moth feeding in bananas, is present at these sites. Monitoring known ‘hot spots’ such as rows adjacent to scrub or creek lines is also a good idea. Banana scab moth has been documented to use Pandanus spp. and Heliconia spp. as alternative host plants.

Managing banana scab moth

Treatment for banana scab moth should be performed year-round as damage results in immediate downgrading or rejection of fruit. Management of banana scab moth is particularly important if heavy bunching is anticipated and/or the forecast weather conditions are favourable (hot and wet).

Biological control

Banana scab moth can be controlled by application of Bacillus thuringiensis subsp. Kurstaki based biopesticides (also known as B.T.) that will not adversely affect other beneficial insects. Some insects (parasitic flies and wasps, ants, spiders and other predators) feed on banana scab moth caterpillars and provide some level of control.

Cultural control

Selecting followers of equal size which equates to synchronised bunch emergence over a block will ensure that the application of chemical control methods is more efficient.

Chemical control

Bell injection is the preferred method of insecticide application to prevent banana scab moth damage. Bell injection is a targeted application of insecticide into the newly emerged bunch and the technique is unlikely to impact beneficial insects on other parts of the plant. The correct site for injection is approximately one third of the way down from the top of the upright, vertically positioned bell. Bells which are injected later than this (i.e., when horizontal) have an increased risk of insect damage.

Initial trial work completed by the Department of Agriculture and Fisheries (DAF) has also indicated that the volume of insecticide applied in bell injection is an important consideration. As insecticides require larger volumes to ensure good coverage, initial trial work showed that using 40mL volume wasn’t sufficient to get appropriate control at times of high pest pressure. It is recommended that growers use a 60mL volume at the specified label (or permit) rate for bell injection to provide adequate coverage.

Always check the APVMA website for current chemical registrations before use. Below are insecticides currently registered (August 2024) and permitted for bell injection to control banana scab moth.

For more information contact:

The Better Bananas team
Department of Agriculture and Fisheries
South Johnstone
13 25 23 or email betterbananas@daf.qld.gov.au

This information is adapted from: Pinese, B., Piper. R 1994, Bananas insect and mite management, Department of Primary Industries, Queensland

Download this information as a fact sheet

This information has been updated as part of the National Banana Development and Extension Program (BA19004) which is funded by Hort Innovation, using the banana industry research and development levies and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture. The Queensland Government has also co-funded the project through the Department of Agriculture and Fisheries.

Banana Scab Moth – general information

Posted on 2024-08-23 by Sarah Williams

Banana scab moth Nacoleia octasema

General information

Occurrence

Banana scab moth is present throughout the year but is favoured by moist and warm conditions, hence the greatest potential for damage is during the wet season. Bunches that emerge from December through to the end of May are most at risk of severe fruit damage. The cooler and drier winter months are relatively free of banana scab moth damage. However, damage can occur if unseasonal rain occurs at this time. Research has shown adult moths do not mate or produce eggs under low humidity and dry conditions.

Description and lifecycle

The tiny (1.2-1.5mm) transparent or yellow flattened eggs are laid in clusters (of up to 30 eggs) that resemble miniature overlapping fish scales. These egg clusters are very difficult to locate because of their small size and the fact that they are laid near the throat of the plant. The eggs are usually laid on the emerging bunch and the surrounding leaves, but eggs have occasionally been found on the pseudostem below the new bunch. Larvae (caterpillars) are pink to brown in colour and range in length from 1.5mm when first hatched to about 25mm when fully developed. If disturbed the larvae wiggle violently and drop on silken threads to avoid predation. When larvae are fully mature they generally pupate in the trash at the base of plants or beneath dry leaf sheaths.

The adult moths are difficult to find due to their small size (22mm wingspan), the fact they hide during the day and their dull brown/grey colouration. Adults are most active at dusk when mating and egg laying occurs. Adults do not appear to be attracted to lights, unlike other moth species. The total lifecycle from egg to mature adult takes around 25-32 days.

Damage

The banana scab moth is a severe pest of bananas and can cause up to 100% damage to the bunch if left uncontrolled.

Feeding by young larvae starts as soon as the first bracts lift and usually increases in severity as the larvae grow and move progressively down the bunch as subsequent bracts open. The feeding causes cracking and scarring to the fruit skin, while severe cases can cause disfigurement of fruit as the fingers enlarge. Damage is usually only superficial, where affected fruit is downgraded or deemed unsuitable for the market.

Damage is usually confined to the outer curve of the fingers (the area nearest to the bunch stalk) but, in more severe cases, damage can extend to the stalk, areas between touching fingers, or even extend to cover the whole fruit surface.

Banana scab moth damage affecting multiple hands, progressing with intensity down the bunch.

Banana scab moth damage evident on back of hands close to bunch stalk.

Banana scab moth damage. Scarring on fruit makes it unsellable to market.

Larvae of banana scab moth also consume foliage and can damage plants where a bunch is absent. This leaf damage is worse in varieties such as Lady Finger and Ducasse and is generally not a problem in Cavendish.

For more information contact:

The Better Bananas team
Department of Agriculture and Fisheries
South Johnstone
13 25 23 or email betterbananas@daf.qld.gov.au

This information is adapted from: Pinese, B., Piper. R 1994, Bananas insect and mite management, Department of Primary Industries, Queensland

Download this information as a fact sheet

This information has been updated as part of the National Banana Development and Extension Program (BA19004) which is funded by Hort Innovation, using the banana industry research and development levies and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture. The Queensland Government has also co-funded the project through the Department of Agriculture and Fisheries.

Spider mites summary

Posted on 2024-07-10 by Sarah Williams

Spider mites

The banana spider mite (Tetranychus lambi) and the two-spotted mite (Tetranychus urticae) which are both commonly referred to as ‘spider mites’ or ‘red spider’, can cause significant damage to banana leaves and even fruit when present at high levels. They are a common pest of bananas, especially over the warmer spring and summer months. Mites feed mainly on the underside of plant leaves, consuming the contents of plant cells. This permanently damages the leaf and reduces its functionality. With moderate to severe mite damage, fruit development can be delayed and occasionally fruit can be marked with a reddish discolouration towards the cushion end.

Early detection and the adoption of practices to help minimise spider mite populations will greatly assist in managing this pest. Click below for more information on management options.

More information

This information has been updated as part of the National Banana Development and Extension Program (BA19004) which is funded by Hort Innovation, using the banana industry research and development levies and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture. The Queensland Government has also co-funded the project through the Department of Agriculture and Fisheries.