The cotton aphid may be troublesome during the seedling stage when its feeding may result in plants being stunted. At the boll-opening stage, the honeydew produced by the insect and the associated fungal moulds can foul the cotton lint. This lowers the quality of the crop and can cause harvesting difficulties. Cotton aphid has a number of predators such as ladybeetles and lacewings, but these are usually eliminated in cotton by insecticide sprays applied to control pests.
Adults are 2 mm long with a rounded body shape, long antennae and two short siphunculi (tube-like projections on either side at the rear of the body). Cotton aphids vary in colour: the first (winged) arrivals are blackish-green and they produce dusky-green to orange nymphs.
Found in all states of Australia.
A female aphid can produce live young at the rate of four to six per day, which in summer can mature into adults in four to seven days and immediately begin producing live young, leading to many generations per year. In Australian cotton regions, cotton aphids persist through winter at low levels of abundance. As temperatures increase, aphid populations begin to build rapidly again.
Adults and nymphs suck sap from growing points. Large numbers can cause leaf distortion and stunting. More significant is the production of honeydew that interferes with photosynthesis and late in the season causes stickiness and discolouration of the cotton.
Cotton aphids also vector cotton bunchy top (CBT), which stunts the growth of cotton plants and can dramatically reduce yield.
|Monitoring and action level|
Aphids prefer younger growth so sampling should begin from seedling emergence and continue at least weekly. Check also for leaves shiny with honeydew or black from sooty mould growing on the honeydew.
Cotton may recover from aphid damage even if high numbers (greater than 90%) of plants are infested, provided the infestation does not persist for more than 10 days. Control should be applied if the standard threshold of 90% of plants infected occurs during the growing season, or slightly earlier if it is clear that aphid populations will soon exceed threshold.
Chemical control: A limited range of insecticides may be applied as foliar sprays. Insecticides may also be applied as seed treatments or as granules with the seed at planting. Care must be taken in selection of insecticides as many populations of cotton aphid are resistant to particular insecticides. For current chemical control options see Pest Genie or APVMA.
Cultural control: A non-host rotation crop (e.g. winter cereal), together with control of weeds, cotton stubble and cotton volunteers, may reduce reservoirs of aphid resistance and disease transmissions.
|Conservation of natural enemies|
A range of parasitoids and predators will help reduce aphid population. Predators of aphids include: ladybird beetle larvae, damsel bugs , bigeyed bugs and the larvae of green lacewings and hoverflies . Wasp parasitoids mummify and kill aphids.
- Pests of field crops and pastures: identification and control. Editor: P.T. Bailey.