The last couple of weeks has seen several reports of aphids infesting faba bean crops in northern NSW and southern Qld.
It is thought that these early infestations have resulted from the warm conditions that we have been experiencing and that the first lot of cold weather, preferably with a frost will kill most of them off.
There is an excellent article now available on the Qld DAFF ‘The Beat Sheet Blog” that talks about both aphids and armyworm in faba bean;
Whilst, there has been little to no work done on the effects of aphids in faba bean at this time of the year in the northern region the following points have been pulled together after several discussions with the key plays.
Thanks to Joop van Leur – NSW DPI and Melina Miles Qld DAFF.
Direct feeding damage;
· The risk of significant crop damage by direct feeding is considered to be low, especially in rapidly growing crops.
This is were it gets very murky with such little experience
· Faba bean is commonly infected with BLRV and BYMV viruses, which can reduce yields if infection occurs during the seedling stages.
· Remember that not every aphid is necessarily carrying virus, infected plants tend to show symptoms around 10-14 days after infection.
· PBA Warda has a higher level of tolerance to BLRV than older varieties, but is not completely resistant.
· Once plants are infected with virus, they will remain infected and act as a source of infection during the spring.
So what should we be doing, spray or not to spray??
As always this decision needs to be made on a case by case basis and some of the things to consider include;
· Take note of the pattern of aphid infestation in a field. Is it confined to the field margins, or is it more widespread across the field, perhaps originating from broadleaf weeds.
· What is the level of natural enemy activity including ladybeetles, hoverflies, lacewings, predatory bugs and parasitoid wasps.
· As the weather cools, the aphid population growth will slow. Whether the aphid populations die out completely during winter, or survive at low levels to build again in spring is unknown.
Regardless of the management strategies that you employ now, close monitoring will be needed in spring to determine the level of virus infected plants within a crop and the level of spring aphid activity, when appropriate management actions may be need to prevent secondary infection and spread of virus within the crop.