Beet Western Yellows Virus in Canola

Beet Western Yellows Virus (BWYV) is an aphid borne virus that can cause yield and quality losses in canola. BWYV has been a major issue in 2014 in SA and western Victoria, but to a lesser extent in southern NSW. BWYV can be found sporadically throughout canola crops in southern NSW in most years.

Early infection of canola during the vegetative phase can have a greater effect on yield and quality, whereas infection later in the season has less impact on yield. Symptoms can be confused with herbicide damage or nutritional deficiency and include stunting, mottled yellowing or reddening of the leaves, as well as thickened, cupped or misshapen leaves.

BWYV is carried and transmitted by aphid vectors including the Green Peach Aphid (GPA), the Cabbage Aphid and the Turnip Aphid. Of these, the Green Peach Aphid is the primary vector with 96% transmission efficiency, whereas the Cabbage Aphid and the Turnip Aphid have only about 14% transmission efficiency.

Insecticide resistant GPA populations have been recorded in South Australia and Victoria. These resistant populations have been suggested as a reason for BWYV causing such wide spread damage in these states. There are very few Green Peach Aphids present in many areas of southern NSW.

Mild, wet conditions during autumn and early winter 2014 in southern NSW, led to large numbers of aphids and a subsequent increase in the identification of BWYV in canola. These conditions also favoured the build-up of beneficial insects which feed on aphids and other insect pests.

There is no benefit in controlling aphids late in the season to suppress BWYV, as yield loss from late infection will be minimal.

If the 2014 season finishes warm and dry, late aphid infestation may occur in canola crops. These will most likely be Cabbage Aphids and Turnip Aphids, rather than Green Peach Aphids. Therefore, the decision to control will be based on an estimate of the feeding damage caused relative to the cost of control.

When considering aphid control, it is important to remember that beneficial insects have also responded to favourable autumn and winter conditions, allowing them to provide good control of moderate aphid populations. In addition, selection of specific aphicides that preserve beneficial insects is a more effective and sustainable option.