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Canola aphids

Canola aphid numbers have increased over the last few weeks in northern Victoria, and have also been reported in other regions. In spring, aphids that colonise canola are most commonly the cabbage aphid (Brevicoryne brassicae) and the turnip aphid (Lipaphis erysimi). Contract services manager, Stuart McColl (BCG), says high aphid populations have been observed in some canola crops around Swan Hill and Quambatook, in the Mallee district of Victoria. Stuart reports that in one paddock, most plants had small colonies of cabbage aphids, with larger colonies of 10-20 cm along the flowering spikes of canola plants found every few metres. Cabbage aphids have also been identified from samples collected from canola crops near Cobram and around Rochester, in the Northern Country district of Victoria, and in canola crops north of Birchip, in the Victorian Mallee.

Preliminary trial work conducted in Western Australia suggests spraying insecticides to control late season infestations of canola aphids is unlikely to be economically viable in many situations. Aphids typically congregate around the late flowers on secondary and tertiary lateral stems of canola plants. Only a small fraction of pod production and yield results from this late growth. Conversely, much larger levels of damage are expected if early colonisation by aphids occurs on the primary and early secondary flowers, which contribute a high proportion of yield.

The intensity of aphid infestation is also important when deciding on the merit of chemical control in spring. Chemical control is usually justified when larger aphid colonies cover > 1 cm of the flowering stems on at least 20% canola plants. If unsure, regularly monitor crops as aphid numbers can increase dramatically under optimum conditions. Aphid infestations are typically patchy, and often heavier on crop edges.

For further information about canola aphid management, click here.

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