Cotton aphid
Cotton aphid is also known as melon aphid in horticultural crops. It can be a major pest of cucurbits where large populations can cause the growing tips and leaves to die. Like in cotton, melon aphid also transmits many viruses including cucumber mosaic virus, papaya ringspot virus and bean common mosaic virus while it is feeding.
Description
The winged adult cotton aphids are typically black, while the colour of the wingless stages can vary from pale yellow to dark green, brown and dull black. To differentiate from other aphid species, green peach aphid is a pale yellow/green and is more tear-drop shaped and the colonies are more uniform in colour than a cotton aphid colony. Cowpea wingless aphids are a shiny black whereas cotton aphids have a duller appearance. There are other differences between the species that can be seen with a hand lens.
Both the nymphs and wingless adult cotton aphids feed on the underside of leaves, in the terminals, on young stems and developing fruits. This feeding damage can result in stunting of the leaves, fruit and terminals and in severe cases, parts of the upper leaf surface will turn red. While cotton aphid is the most common aphid pest, green peach aphid can cause more severe stunting with a smaller population of aphids.
Control
As cotton aphid has developed widespread resistance to many insecticides, it is important not to rely on insecticides alone and where available, consult industry Insecticide Resistance Management Strategies. In cotton, it is recommended that aphid levels be monitored at least weekly from seedling emergence through to defoliation.
Controlling brassica weeds and other hosts such as marshmallows, capeweed and thistles between seasons will help reduce aphid pressure.
Cotton aphid populations build rapidly as spring temperatures increase. At this time, beneficial insects can play a very important role in suppressing aphid populations, so it is important to consider their populations too when assessing aphid spray thresholds.
In addition to beneficial numbers, consider the current growing conditions. If crops have good growing conditions at the time of infestation (i.e. good soil moisture), they are more likely to be able to compensate for aphid damage compared to moisture stressed plants.
Movento® is soft on many beneficial insects, including parasitic wasps, pirate bugs, hoverflies and lacewings when used as directed. It is registered for the control of cotton aphid in cotton, celery, rhubarb, cucurbits and herbs.
References
AUSVEG (Viewed Oct 2019), ‘Aphid pests in vegetable crops’, https://ausveg.com.au/biosecurity-agrichemical/crop-protection/aphids/Cotton Australia (2018), ‘Cotton Pest Management Guide 2018-19’, https://cottonaustralia.com.au/uploads/resources/IRMS_Pages_from_CPMG_201819.pdf
Cotton Catchment Communities CRC (2008), ‘Aphid ecology in cotton’, Inside Cotton: On Farm Series: How to Cotton Insects,
http://www.insidecotton.com/jspui/bitstream/1/111/1/Aphid_Ecology2008b1.pdf
PestNet (Viewed Oct 2019), ‘Pacific Pests and Pathogens Fact Sheets: Melon aphid’, http://www.pestnet.org/fact_sheets/melon_aphid_038.htm
The State of Queensland (2019), ‘Aphids’, https://www.business.qld.gov.au/industries/farms-fishing-forestry/agriculture/crop-growing/pests-field-crops/aphids