Cabbage aphids

Agronomist, Greg Paul (IMAG Consulting), reports finding cabbage aphids (Brevicoryne brassicae) in several canola crops near Forbes, in the Central West Slopes and Plains district of New South Wales. Greg says numbers are quite variable between paddocks but in several cases there has been a distinct increase in numbers as the crops reach late-flowering. Cabbage aphids have also built up to significant numbers requiring chemical control in some crops in the Mallee and Northern Country districts of Victoria.

In the Western district of Victoria several agronomists have reported finding very few (if any) cabbage aphids in the majority of canola crops inspected recently. Researcher, Sommer Jenkins (cesar), also reports finding very few cabbage aphids in two canola trials (or in the surrounding crops) near Geelong and Ararat, also in the Western district of Victoria.

Cabbage aphids grow up to 3 mm in length and have a dull grey-green body. Infestations start when winged aphids fly into the crop from autumn weeds. These give rise to dense colonies, which appear bluish-grey and are covered with a fine, whitish powder. Cabbage aphids suck sap and can reduce yield when numbers are high. A large amount of sugary solution is also secreted which can sometimes lead to black sooty mould, thereby reducing the plants’ ability to photosynthesize and decreasing plant growth. Greater aphid build-up leading to higher yield losses is more likely when crops suffer moisture stress.

Canola is particularly susceptible to aphid damage during bud formation through to late flowering, therefore, it can be important to control aphids to prevent heavy infestations. If chemical control is necessary, use ‘softer’ chemicals (such as pirimicarb), which are aphid-specific and less harmful to other insects. Predators and parasites should be encouraged as a natural way of suppressing aphid numbers. These are a very reliable form of control during the warmer days of spring and when low to moderate numbers of aphids are present.

Click here for images of cabbage aphids.