Canola aphid

Populations of aphids in canola crops have risen steadily over the past 2-3 weeks in widespread areas of Victoria and southern New South Wales. Agronomist, Doug Perryman (Rodwells & Co), has reported finding aphids in most canola crops around the Boort area, in the Northern Country and Mallee districts of Victoria. The aphids are currently only present on the edges of crops, with very few found 4-5 m into the paddock. The worst affected plants have colonies of aphids up to 7-8 cm long, however Doug says there is no concern about significant damage and control is currently not warranted. In addition, this week’s rainfall is expected to slow population growth and will provide moisture in the soil to help plants outgrow feeding damage.

Agronomist, Greg Toomey (Landmark), reports similar levels of aphid activity in canola crops around Elmore, in the Northern Country district of Victoria. Greg says aphids are easily found in most crops, with some colonies up to 20 cm long observed on occasional plants. Field marketing agronomist, Neil Durning (AGnVET), says aphids have also become prevalent around the Wagga Wagga area, in the Riverina and South West Slopes districts of New South Wales. In this region, most canola crops are approaching the end of flowering and Neil says the aphid infestations do not warrant control at this stage. Agronomic consultant, Baden Dickson (AgmanGroup), reports an increase in aphid numbers in the past fortnight in canola crops south west of Forbes, in the Central West Slopes and Plains district of New South Wales. We have also received reports of low, but increasing populations of aphids in canola crops in the Western district of Victoria.

In canola, there are two commonly occurring aphid species that form distinctive clusters around the flowering spikes of plants. Cabbage aphids (Brevicoryne brassicae) and turnip aphids (Lipaphis erysimi) are similar in size and appearance, and affect crops by sucking moisture and nutrients from plants. Cabbage aphids are about 3 mm long and dull grey-green in colour. Colonies appear bluish-grey and are covered with a fine, whitish powder. Turnip aphid colonies may have a light covering of wax however this is much less obvious than the thicker powdery covering of cabbage aphid colonies.

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. 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. The impact of aphids will be far more pronounced in crops that are moisture stressed, whereas adequate soil moisture can mean crops suffer little or no yield loss even with high aphid populations. If chemical control of aphids is required, selective insecticides (such as pirimicarb) are available, which are aphid specific and less harmful to beneficial insects and other invertebrates.