Cereal Aphids

High numbers of corn and oat aphid have recently been reported in many cereal crops.  These aphids are collectively known as cereal aphids.

The increase in numbers is a result of warmer than average temperatures plus humid conditions during late winter.  Assuming these conditions persist, it is likely that numbers will continue to build in the short term.  However, aphid numbers within crop can also decline rapidly at this time of year, in the event of cold conditions or heavy rainfall.

Cereal crops can withstand relatively high numbers of aphids without suffering yield loss.  Published economic thresholds are in the order of 15 aphids per tiller on 50% of the tillers.

In some cases, late infestations between booting and milky dough stage can result in yield loss.  However, infestations after grain fill are unlikely to affect yield.

When cereal crops are not stressed and growing conditions are good, the value in spraying aphids is questionable.  Whilst aphids can be controlled, the crop could be re-infested quite quickly.  In addition, the crop may become less attractive to aphids as it moves from the vegetative stage to the reproductive stage, resulting in the aphids moving to a more attractive host.

In the event that crops do require spraying, aphicides that control aphids with minimal effect on beneficials are preferred.  Broad spectrum insecticides kill all of the beneficial insects, allowing the aphid population to rebound more quickly post spraying.

References

• McDonald G, Govender A & Umina P. PestFacts south eastern (19 August 2016). Cesar Pty Ltd.