Recent surveys in cotton growing areas have found a wide variety of aphids present, but varying in their numbers and likely impact.
Dr Lewis Wilson, Senior Principal Research Scientist, and Ms Tanya Smith, a Technical Assistant with CSIRO Plant Industry and the Cotton Catchment Communities CRC, report the presence of green pea, turnip, corn leaf, sow thistle and brown sow thistle aphids, and low numbers of cotton, cow pea and green peach aphids.
Commenting on the weekly CSD Web on Wednesday video program, Tanya Smith said that pea aphid was particularly abundant, coming off legumes such as the medics, as were the two aphids that use sow thistle as a host.
She said growers should scout crops to assess if aphid populations are breeding and producing offspring, which would indicate that they are likely to be a species that attacks cotton, such as cotton aphid, cowpea aphid or green peach aphid. Many aphids that do not attack cotton will settle on cotton temporarily to test feed, but will find it unsuitable and move on she said.
She noted that fields most vulnerable to aphid infestation include those that have not been kept clean, where the weeds have been let go, and particularly fields with cotton that's come through from previous seasons. She also included that this allows the aphids to over winter and then they can go straight from the weeds on to the cotton crop which is coming through.
Tanya Smith said there are large numbers of aphid predators and parasites around, due to the aphid populations on the abundant weeds. These include hoverfly larvae, ladybeetles, parasitic wasps and predatory bugs, and they will often control aphids on cotton.
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