Pest management of bananas in the ORIA

Banana weevil borer

Damage from the Banana weevil borer (Cosmopolites sordidus) is confined to the corm of the plant. Tunnelling is not visible as the larva remains inside the corm. Signs to watch for are reduced plant growth, yellowing leaves, weak or dying suckers and choking.

Plants may also break at the corm and fall over, revealing the tunnels inside the corm that can also often be blackened inside, and have white larvae in the tunnels. The major mode of spread is infested planting material. Plantations should be monitored regularly for the presence of the adult beetle.

Plantation trash should be kept free from all plant rows when the weevil is present, to enable detection and effective spray application. Critical times to monitor are October/November and March/April.

To assess the level of the pest in the plantation, freshly cut disks of banana stem or corm that are attractive to adult weevils are used. The disks should be around 10m thick and cut from spent stems. They are then placed on the ground at the base of stools, covered with leaves and left undisturbed for five days. The weevils that are attracted to the bits can then be counted.

At least 20 traps per hectare should be used and if an average of four or more weevils per trap are detected then chemical control is recommended.

Sugarcane bud moth

Sugarcane bud moth (Opogona glycyphaga) causes mainly cosmetic damage to the skin of the fruit. The larvae feed on the surface of the fruit when all the bracts have fallen off. The damage is usually limited to the tips of the fingers.

The pest is most abundant between December and April. Due to its size, it is very hard to detect. The eggs are too small to be seen, the larvae are yellow to dark grey and are around 16mm long before pupating. The pupa is found near the feeding site and has a silken cocoon covered by black pellets of excreta. The adult is a colourful moth and has golden yellow and purple wings 10mm long.

The adults rest during the day on the banana plants and are not often seen due to their small size. The adult moths are attracted to light therefore it should be possible to monitor for this pest with light traps.

Pest management incorporates a pest block at the time when the bunch cover is applied. The pest block is a 40mm x 40mm block of canite or chipboard that is soaked in a 1:4 solution of chlorpyifos (500g/L) in water for 24 hours and then air-dried.

The block should be touch-dry before being attached using a galvanised nail, to the stem of the bunch or being stapled to the inside of the bunch cover. There should be no contact between the pest block and the stem or fingers of the bunch.

The block should be located well inside the bottom of the bunch cover and attached at bagging. There is a maximum of two blocks per bunch. Blocks can be used one or twice but have to be resoaked before use the second time. There is no withholding period for the fruit using this treatment.

Russet mite and two-spotted mite

Russet mite (Brevipalpus phoenicis) and two-spotted mite (Tetranychus urticae) can both cause problems.

Mites usually damage fruit during the dusty, drier conditions from May to October. Damage is most serious following high temperatures and adjoining roads. Mite damage first occurs on the underside of the leaves and appears in isolated bronzy patches. With larger infestations the mites move onto the bunches and damage the fruit. The feeding causes speckles on the skin that produce a rusting effect in severe cases, and after a while the fruit surface will dry out and crack. Seriously damaged fruit from russet mite should not be packed.

Control can be achieved by regularly spraying with a suitable miticide, but pest resurgence can be a consequence. Care should be taken in spraying miticide on young bunches or during hot weather, as damage can result.

The mite-eating ladybird, Stethorus, is an important biological control in bananas. As their numbers build up they tend to bring mite populations under control.

For the russet mites the ‘pest block’ method is also effective for its control on the fruit at bagging and can avoid many of the problems of miticide spraying. See the description under sugar cane bud moth for production of a ‘pest block’.

Nematodes

Nematodes are tiny microscopic worms that can attack and damage a plant’s root system. By themselves nematodes can travel through the soil at about 1 metre per year. However, they can infest larger areas more quickly through the movement of mud on machinery, boots and animals; and by water movement carrying them to new sites.

Infested plant material is the most common way that nematodes move from one site to the next. Planting material that is infested is extremely difficult to treat to fully remove all nematodes.

In many cases, nematode-infested plants tend to grow more slowly, their bunches are smaller and their bunching cycle is longer. The characteristic sign of burrowing nematodes is plant toppling. However, other pests and diseases can cause a plant to topple, for example the banana weevil borer.

• Looking at how bad the nematode problem is, how large a loss of yield will it cause?
• How much will it cost to control the nematodes?
• What will be the eventual increased return from any extra bananas gained from treating the nematodes?

Nematicides that are registered for bananas are applied to the soil or plant and help to reduce high populations of plant parasitic nematodes. Nematicides are highly toxic chemicals so care needs to be taken when applying them.

Organic and biological controls are still being tested in Australia with limited success. Fallow crops can also be host species for nematodes so non-host plants should be planted to prevent nematodes multiplying. Nematodes are not thought to be a significant pest in ORIA banana production areas.

Grasshoppers

Grasshoppers are a sporadic problem on developing bunches, usually after the wet season. Sometimes severe damage to individual bunches can result due to the hoppers feeding on the banana skins. Laying out maize baits around blocks can give effective control, and in plague proportions sprays can be used with extreme caution.

Fruit bats and rats

Native colonies of fruit bats are found in the Kimberley. In the late dry season (September-November) when native food sources can be scarce, this vertebrate pest may attack newly emerging bunches and even developing bunches. They can climb inside a bunch cover and cause severe damage by feeding and clawing fingers. No foolproof method of control exists. Because seasonal conditions vary between years, fruit bats do not cause commercial damage every year.

Rats will do similar damage to the fruit bats.

Permission from the Department of Parks and Wildlife (Kununurra Office) is required to conduct control programs on fruit bats.

Exotic pests

Spiraling whitefly (Aleurodicus dispersus) and banana scab moth (Nacoleia octasema) have been identified as potential threats. Following quarantine and biosecurity guidelines is essential to ensure these pests do not enter the ORIA.