Aphids

With the onset of warmer daytime temperatures, it is now time to begin thinking about potential spring pest issues this year. Agronomic consultant, Baden Dickson (AgmanGroup), has reported finding 2-3 aphids on the flowering spikes of 10-20% of plants in numerous canola crops north west of West Wyalong, in the Central West Slopes and Plains district of New South Wales. Baden says the crops are now at the late-flowering stage and control is not necessary at this point in time.

In Victoria, very low numbers of cabbage aphids (generally < 5 aphids sporadically found on occasional flowering spikes) have been seen in canola crops in parts of the Wimmera, Mallee and Northern Country districts. Although we have so far received relatively few reports of aphids, be aware that insect populations are incredibly dynamic and numbers can build up very rapidly under favourable conditions.

In canola, cabbage aphids (Brevicoryne brassicae) and turnip aphids (Lipaphis erysimi) are the most problematic species in spring. Both of these species form dense clusters around the flowering spikes, and their impact on crops is far more pronounced when crops are moisture stressed. This is because they feed by sucking moisture and nutrients from plants, which can result in yellowed patches of plants or poor pod-fill. However if soil moisture is abundant these aphids may be present in relatively high numbers with seemingly little (if any) impact on yield.

In cereal crops, oat aphids (Rhopalosiphum padi) and corn aphids (Rhopalosiphum maidis) are the predominant spring pests. The impact of aphids on winter cereals (yield and quality) is the result of a complex relationship that involves the timing of infestation, aphid density, where on the plant the aphids feed and crop physiology at the time of infestation. There is no impact on yield after grain has filled and is maturing. Infestations that occur during booting to milky dough, particularly where aphids are colonising the flag leaf, stem and ear, can result in yield loss. Heavy infestations cause the crop to turn yellow, become stunted and generally show poor vigour.

In pulses, the cowpea aphid (Aphis craccivora) forms dense colonies on the growing tips and can occur in faba beans, lentils, and lupins, as well as lucerne and clover. Other species that may also be present in pulses are the bluegreen aphid (Acyrthosiphon kondoi) and the pea aphid (Acyrthosiphon pisum). Like canola, aphid damage in pulses crops is amplified in moisture stressed crops.