Banana spider mite

Banana spider mite is the most important and widespread of the mite pests of bananas.

Activity is mainly confined to the dry spring to summer periods where specific miticides may be required. High humidity does not favour mites and mite pressure in north Queensland reduces accordingly in the wet season. Severe outbreaks are usually associated with aerial or cover sprays of broad-spectrum insecticides. Outbreaks of the mites are usually localised within a plantation. The warm, dry conditions under plastic bunch covers are particularly favourable for build-up of banana spider mite.

Scientific name

Tetranychus lambi

Description of adult

Adults are usually less than 0.5mm in length, have 8 legs and their spider-like appearance can just be made out with the naked eye. The banana spider mite is similar to the two-spotted mite. The banana spider mite is more straw coloured and lacks spots. The main distinguishing feature between the 2 species is the lack of fine webbing in infestations of the banana spider mite.

Immature stages

The clear, very small spherical egg is followed by 3 immature stages that are similar to the adult stage.

Life history

The life cycle can be completed in 1–4 weeks, depending on temperature and there are many overlapping generations each year. Populations increase rapidly in hot dry weather. All stages of the life cycle plus cast skins and dead mites occur together, mostly near the veins of the underside of leaves but with high numbers can extend over the whole leaf and fruit.

Distribution

Throughout Queensland.

Host range

Banana.

Damage

Mites are a minor and frequent pest of bananas.

Mites suck out the cell contents causing cell breakdown. Damage is mainly confined to the underside of lower older leaves; however, in severe outbreaks the mites can move onto the bunches and damage fruit. Leaf damage first appears as isolated rusty patches, which later coalesce along the leaf veins as the infestation increases. Eventually the whole leaf turns brown-grey and, in extreme cases, the leaves wilt, with partial or total collapse of the leaf lamina. Leaf wilting and collapse result in sunburnt bunches and reduction in plant growth.

Fruit damage by banana spider mite is found mainly on the cushion end of the fingers, close to the bunch stalk. Feeding in this area causes a dull red to purple-black discolouration of the fruit surface that may later dry out and crack.

More severe infection will result in the damage spreading over the entire fingers

Control

Monitoring should be carried out fortnightly during hot dry conditions and otherwise at intervals of 3 weeks. Action thresholds have yet to be determined, but if mites are found on the young leaves and dry to hot conditions are expected, a treatment should be applied to prevent damage. Miticides are most efficient if applied early in the infestation.

Cultural

Reduce dust on roadways as much as possible because dusty conditions favour the build-up of mites. Broad-leafed weeds act as reservoirs for mites, which can infest banana leaves following treatment, so maintain a good level of weed control.

Good water management, especially during dry conditions, will reduce water stress to plants, allowing them to better withstand mite damage.

Regular desuckering, leaf trimming and maintenance of correct plant densities will assist in achieving good spray coverage and thus increase the level of control obtained with miticides.

Biological

The small, shiny black mite-eating ladybird beetle predator, Stethorus spp. is the most important predator of mites in bananas. Both larvae and adults feed on the mites. When mite populations are high the black pupae of the ladybird may often be seen as a line on either side of the midrib. Other predators include other ladybird beetles, native predatory mites, predatory thrips and rove beetles. Releases of the predatory mite, Phytoseiulus persimilis, in bananas have not been successful against the banana spider mite in northern Queensland.

Cover sprays with broad-spectrum insecticides are the major cause of mite flare-up because they destroy the natural predators. Some fungicides used to control leaf disease in bananas also affect the predators. Where non-disruptive (pest-selective) pesticide treatments are used, natural predators usually provide sufficient control and miticides should not be required.

Chemical

A spray may be required if there is noticeable bronzing on young leaves (leaf No.3 and above), if natural predators are not evident and if dry and hot weather conditions are expected to continue. Spray only when plants are not suffering heat/moisture stress, because if leaves are wilted, coverage of the mites on the undersurface of leaves is difficult. Do not exceed recommended rates and volumes or fruit 'burn' may result. Good mite control can be achieved by well timed miticide treatments using correctly calibrated sprayers or misting machines. Sufficient volume (up to 500 L/ha) has to be applied to obtain good coverage of leaf undersurfaces where the mites occur. In most situations a second application 14 days later should be applied, especially if monitoring indicates a carryover of mites. This second application may not be required if a thorough first application of an ovicidal miticide was applied, or if high populations of Stethorus lady beetles are found during monitoring after the first treatment.

Chemical registrations and permits

Check the Australian Pesticides and Veterinary Medicines Authority database for chemicals registered or approved under permit to treat this pest on the target crop in your location. Always read the label and observe withholding periods.