The Grains Research and Development Corporation (GRDC) has sounded a warning to northern region grain growers to be ‘on alert’ for increases in aphid numbers in the lead up to spring.
Aphid population development has been high this year following the unusually mild and dry start to the winter season, particularly in faba bean and other early sown crops like canola and cereals which experienced high aphid pressure up until the onset of cold temperatures and frost in early July.
While the recent cold weather has impacted aphid numbers and activity, the pressure earlier in the season means that there is a level of primary infection in some crops which could escalate rapidly if aphid numbers build significantly in spring.
According to NSW Department of Primary Industries plant pathologist Joop van Leur, testing to identify the virus species present in faba bean is still in progress however early indications are that the main virus present is Bean yellow mosaic virus (BYMV) with smaller incidences of Bean leafroll virus (BLRV) and other luteoviruses.
“It is important to remember that not every aphid that lands in a faba bean crop is necessarily carrying virus. Virus symptoms will appear in crops around 10 to14 days after infection,” Mr van Leur said.
“Symptoms of BYMV are typically vein yellowing and green-yellow mosaic veins and once faba bean plants are infected with virus, they will remain infected.
“Plants infected in autumn become sources of virus in spring, although (depending on the virus) the impact of the virus on yield will be lower if infection occurs in a later stage of crop development.
“In-crop aphid management becomes more important in paddocks where autumn virus infections have taken place.”
If the dry conditions continue in August, high aphid activity may be expected. Later sown pulse crops like chickpeas are particularly vulnerable to virus infections carried by spring aphid flights.
Consultants and growers are being urged to monitor aphid populations closely in the lead up to spring and implement control strategies early to avoid severe virus infection later in the season.
Pulse Australia national manager Gordon Cumming said it was difficult to predict the likely severity of virus infection in pulse crops in the lead up to spring but said early detection and control would be the most effective means of avoiding yield loss.
“Growers and their agronomists need to be ready to take action on aphid numbers earlier than normal given that primary infection already exists,” Mr Cumming said.
In response to concerns over the potential for high aphid activity in spring, an Emergency Use Permit (EUP) for pirimicarb in winter pulses has been approved by the Australian Pesticides and Veterinary Medicine Authority (APVMA).
If aphid control is warranted, Department of Agriculture, Fisheries and Forestry (DAFF) Principal Entomologist Dr Melina Miles urged growers to consider the ‘softest’ option first.
“Pirimicarb is the only selective aphicide available and it is very effective in controlling aphids whilst preserving the beneficial insects which can then mop up any aphids that might survive the treatment or reinvade,” Dr Miles said.
“The use of broadspectrum options like dimethoate and synthetic pyrethroids will kill both the aphids and the beneficial population.
“Beneficials are important in suppressing other pest species that may occur in spring, particularly helicoverpa. Without a good beneficial population it is more likely that helicoverpa populations will require treatment.”
The pirimicarb EUP is valid until October 31, 2014 and stipulates a use rate of 250 – 300 grams/hectare with a withholding period to harvest of 21 days. A copy of the permit can be found at http://permits.apvma.gov.au/PER14981.PDF.
Growers should consult their agronomist or consultant to determine the most appropriate strategy for aphid control or more information on BYMV visit the recently released GRDC GrowNotes for faba beans www.grdc.com.au/GrowNotes.
Joop van Leur, plant pathologist NSW DPI, Tamworth
02 6763 1204, 0427 928 018
Gordon Cumming, Pulse Australia national manager
0408 923 474
Elise McKinna, DAFF Media & Communication Officer
07 3087 8576
Sarah Jeffrey, Senior Consultant Cox Inall Communications
0418 152 859