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Canola aphids

Sales manager, Richard Fraser (Pioneer Hi-Bred International), reports finding aphids infesting canola crops south of Goondiwindi, in the North West Slopes and Plains district of New South Wales. The aphids are colonising the flowering spikes of canola plants, indicating they are either cabbage aphids (Brevicoryne brassicae) or turnip aphids (Lipaphis erysimi). These two species are the most common aphids found in canola crops during spring.

Cabbage aphids and turnip aphids 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.

Agronomist, Mick Duncan (Northern Agriculture), has also observed aphids starting to build up in numbers within canola crops around Tamworth, in the North West Slopes district of New South Wales. Mick says aphids were largely seen in advanced flowering crops, and were more plentiful near brassica weeds and the edge of crops. The aphid populations tended to drop off significantly away from paddock edges. Control is not warranted as the numbers are below accepted threshold levels.

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. Click here for further information on beneficial insects to look out for this spring.

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