A VIRUS in faba beans that has previously only caused mild damage in Australia has been so severe in northern NSW that it has forced growers to plough in some crops.
Joop van Leur, senior plant pathologist with NSW DPI, based at Tamworth, said bean yellow mosaic virus had been observed at unprecedented levels and at much higher rates of severity than had ever been observed here.
Mr van Leur said plant pathologists were working to establish what had led to the disease, which is spread by aphids, being so severe this year.
"We don't know for sure yet, but we are investigating the wet start to the year and the early sowing of faba bean crops" Mr van Leur said.
"It could be that the crop has been damaged so severely as the virus has hit at an earlier stage of the plants' lifecycle than it does normally."
Faba beans are a relatively small but emerging industry in northern NSW and have become a useful agronomic tool, valued by growers for their ability to be planted early.
Mr van Leur said aphid numbers built up rapidly in the first quarter of the year, spurred by good rain and mild temperatures.
They were still present in big numbers into autumn, using introduced naturalised medics species as a host.
"Medics may play a key role in this epidemic as they can be a symptomless host for the disease."
Aphid numbers died down in winter but the damage may have already been done and the plants infected.
The disease presents, as is in the name, with a yellow mosaic pattern emerging on plant leaves.
Mr van Leur said there was a range of severities among infected paddocks but said the worst impacted had been green manured already.
"Certainly not every paddock has been this badly hit but there definitely are some where farmers are choosing to spray the paddock out due to the low yield potential."
Dr van Leur said while it was a huge problem this season, he was not necessarily concerned about the disease having a severe impact every year.
"We were confronted with unique circumstances earlier in the year, with such a lot of rain and such an early plant and these two factors together may be the reason the disease is presenting in such a severe way."