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Canola aphids

Over the last few weeks there have been reports of aphids persisting in high numbers on emerging canola crops. Agronomist, Adrian Dunmore (Rodwells), has reported issues in a 2-leaf canola crop east of Deniliquin, in the Riverina district of New South Wales. The aphids were present in variable numbers, ranging from 0 - 10 per plant. The aphids are either cabbage aphids (Brevicoryne brassicae) and/or green peach aphids (Myzus persicae). The paddock has recently been sprayed with a synthetic pyrethroid, which controlled the majority of aphids, although Adrian says there are still low numbers present. Agronomist, Peter Spencer (IK Caldwell), has reported high numbers of aphids in canola crops across many paddocks around Barooga, in the Riverina district of New South Wales. Peter says several species of aphids have been observed. Besides the green peach aphid and cabbage aphid, the other important canola species is the turnip aphid (Lipaphis erysimi). Many crops in the Riverina district have been under moisture stress, which will limit the capacity of the canola plants to grow away from the feeding damage. There is a belief that in some paddocks, the canola may have been treated with an insecticide seed dressing, although this is currently being investigated further.

Green peach aphids are a pest of many crops, but have a preference for crucifer vegetables, oilseeds and some pulses, such as lupins. Unlike cabbage aphids and turnip aphids, which form dense clusters, green peach aphids are usually sparsely distributed within a crop, mainly on the undersides of leaves. Green peach aphids are an important vector of plant diseases in canola and pulse crops, such a cucumber mosaic virus, bean yellow mosaic virus and beet western yellows virus. Studies of the relationship between virus infection and yield have shown that when aphids arrive early in the season, a combination of BWYV and green peach aphids can cause yield losses of up to 50% in canola. The green peach aphid does have a high propensity to develop resistance to insecticides, and can occasionally present control difficulties.

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