SPRING aphid pressure is expected to be strong this season as the Department of Agriculture and Food (DAFWA) ask farmers to step up their crop inspections in light of the Russian wheat aphid (RWA) outbreak in South Australia and Victoria.
DAFWA PestFax has reported widespread oat aphid activity in wheat crops across northern, central and southern Wheatbelt shires.
It asked growers to be aware of all aphid activity in their paddocks and to be ready to act as temperatures increase into spring.
DAFWA development officer in agricultural entomology Dustin Severtson said significant aphid pressure was expected in canola and cereals this season due to the extensive green bridge over summer.
"In the first part of the season the only real problem with aphids is the transfer of viruses into the crop as they rarely cause feeding damage this early on," he said.
"For growers who have managed fungal disease risk with fungicide coatings when seeding these viruses shouldn't be a problem.
"However, DAFWA field trials have demonstrated a greater than 90 per cent yield reduction in canola when cabbage aphids infested later sown crops.
"This heavy damage would generally not occur evenly across entire paddocks unless plants were very moisture stressed which favours aphid reproduction and spread."
Glasshouse trials show one cabbage aphid can breed up to 15 aphids per week in favourable conditions.
Mr Severtson said high amounts of damage from cabbage aphids in spring is usually aggregated along field edges and where wild radish weeds were present and hosting cabbage aphids.
Those spraying too early to control aphids could also run into problems with re-infestations this year.
To help make decisions regarding insecticide applications, Mr Severtson is developing a mobile app for growers to use when sampling.
As part of his post-graduate studies, Mr Severtson developed a sequential sampling plan that could help reduce the need to spray an entire paddock if only one area had been infested.
His research has developed a 20pc infestation threshold for whether to "watch or spray".
If infestations are below 20pc in the paddock, a watch and keep sampling approach is advised.
Above that threshold and growers need to act and spray.
"This method helps make the farmer's job easier to protect the crop from aphids," he said.
"It's a really hard task if you have massive paddocks and you have to work out if they are infested, what level of infestation there is and how much economic damage is likely to incur."
The app could be used as growers inspect the paddock, recording the results and correlating with a GPS location.
It could lead to growers being able to reduce insecticide sprays to only part of the paddock as opposed to an application across the entire paddock, allowing beneficial predators such as ladybird beetles and lace flies to help reduce aphid populations.
DAFWA is also developing modelling tools to show the link between the green bridge over summer months, aphids and viruses.
DAFWA senior research officer Art Diggle said the GRDC-funded work could be an additional decision support system to be added to DAFWA's suite of online tools.
He said the appetite for research into the link between aphids and viruses had increased following the beet western yellows virus which affected large tracts of canola crops in South Australia and Victoria's Wimmera and Mallee regions in 2014.
The virus spread was caused by early infestations of green peach aphids.
"Aphids are an important vector in moving viruses into crops," Dr Diggle said.
"This research could also help in understanding the drivers of Russian wheat aphid."
