Cabbage aphids

Cabbage aphid populations have begun building up in canola crops and brassica weeds along roads and fence-lines. Agronomist, Andrew Reardon (JJS Glass & Co), reported cabbage aphids across a number of canola paddocks around Junee, in the South West Slopes district of New South Wales. Andrew says the aphids are beginning to form small colonies (20-30 mm in length) on the flowering spikes of isolated canola plants. Agronomist, Warwick Nightingale (DeltaAg), has reported low numbers of cabbage aphids in canola crops around Lockhart, in the Riverina district of New South Wales. cesar consultants have also observed multiple infestations within canola crops around Skipton, in the western district of Victoria. Reports received to date suggest chemical control is not warranted as the numbers are below accepted threshold levels.

Like all aphids, cabbage aphids (Brevicoryne brassicae) affect crops by sucking moisture and nutrients from plants. They are approximately 3 mm long and dull grey-green in colour. Colonies appear bluish-grey and are covered with a fine, whitish powder. When checking for aphids in canola, it is important to check representative parts of the entire paddock, and to look for aphids on a minimum of 20 plants at each point. The impact of aphids will be far more pronounced in canola crops that are moisture stressed, whereas adequate soil moisture can mean crops suffer little or no yield loss even with high aphid populations.

Canola crops are most susceptible to aphid damage from bud formation to late flowering when heavy infestations can lead to wilting, flower abortion and reduced pod set. Control measures should be considered if more than 20% of plants are infested across a wide area. However it is important to consider factors such as crop stage, soil moisture and forecast weather conditions, as these can all influence aphid population build up and crop susceptibility. If unsure, regularly monitor crops as aphid numbers can increase dramatically under optimum conditions.

If chemical control is required, pirimicarb is recommended because it is aphid specific and much less harmful to beneficial insects. Click here for further information about management of canola aphids.