GRAINGROWERS are being encouraged to hold off spraying crops infested with Russian wheat aphid unless aphid populations and crop damage warrant such action.
RWA numbers have been relatively low in the majority of infested paddocks to date and recent heavy rainfall has curtailed infestation levels and activity.
SARDI entomologist Greg Baker said it was important that growers refrained from spraying crops unnecessarily.
“Population levels are substantially below the preliminary economic thresholds on most properties,” he said.
“Occasionally we are seeing paddocks where that is not the case, but those are the exceptions.”
Growers have been advised to follow international advice, which supports an economic threshold of 20 per cent of plants infested up to the start of tillering and 10pc of plants infested thereafter. These thresholds have yet to be validated under Australian conditions.
Growers are being discouraged from spraying, unless deemed necessary, because: sprays provide no meaningful residual control; insecticides may reduce numbers of predators and other beneficials potentially resulting in a spike in numbers of RWA (and other insect pests) as temperatures increase; and spraying can also foster resistance development.
Dr Paul Umina from cesar (a Vic-based scientific research organisation) said although RWA was not posing a high risk to crops at the moment, it was important for growers to remain vigilant and advise authorities of suspected infestations.
Growers and agronomists are asked to take an image of the pest and its damage and to report any suspected new infestations by phoning the Exotic Plant Pest Hotline (1800 084 881) so that the range and rate of spread of the pest can be monitored. Samples of the aphids might be requested for identification.
A RWA National Technical Group, comprising experts from across the country, has been set up by Plant Health Australia as part of the National Management Plan, which will identify immediate control options and needs as well as longer term research, development and extension requirements.
Meanwhile, the GRDC is continuing to encourage graingrowers to adopt a simple four-point plan in dealing with RWA.
The “FITE” strategy revolves around four basic principles:
- Find (look for characteristic leaf streaking or rolling symptoms on cereal crops and grasses)
- Identify (positively identify RWA in consultation with an industry specialist)
- Threshold approach (consider international thresholds for control, factoring crop growth stage, yield potential and potential yield losses)
- Enact an appropriate management strategy that where possible encourages beneficial insects and protects honeybees.
“The GRDC will be making a significant investment in a range of research, development and extension activities that will enable development of an integrated management approach and fill the gaps in current understanding of pest biology, population dynamics and specific control options,” GRDC Grower Services southern manager Craig Ruchs said.
“Entomologists and other industry experts will closely monitor the RWA situation in the coming months to develop an improved understanding of how this pest behaves, its impact and suitable approaches to management under Australian environmental conditions and cropping systems.”
Trials are already under way to compare insecticide treatments in barley and wheat – the two crops most affected by RWA.
Since being detected for the first time in Australia on a property in SA’s Mid North in May, RWA has now been confirmed in a number of SA and Vic cropping regions. The pest is considered notifiable in all other states and territories.
A current map of RWA in Australia is available here.
