Winter weather slows Russian wheat aphid populations
Author: Sharon Watt | Date: 14 Jul 2016
Grain growers in Victoria and South Australia are being encouraged to hold off spraying crops infested with the newly introduced Russian wheat aphid (RWA) unless aphid populations and crop damage warrant such action.
RWA numbers have been relatively low in the majority of infested paddocks in both states to date and recent heavy rainfall events have curtailed infestation levels and activity.
Greg Baker from the South Australian Research and Development Institute (SARDI*) says it is important that growers refrain from spraying crops unnecessarily.
“Population levels are substantially below the preliminary economic thresholds on most properties,” said Mr Baker, whose research into RWA is valued by the Grains Research and Development Corporation (GRDC). “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 percent of plants infested up to the start of tillering and 10% of plants infested thereafter. These thresholds have yet to be validated under Australian conditions.
Dr Paul Umina from cesar (a Victorian-based scientific research organisation) says that in the majority of infested paddocks in Victoria, aphid numbers are reportedly low and spraying is therefore unlikely to be warranted.
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 Umina 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 on 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.
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 Victorian cropping regions. The pest is considered notifiable in all other states and territories.
Its presence has been confirmed on SA’s eastern Eyre Peninsula and the Yorke Peninsula, in the Upper, Mid and Lower North, Murraylands, Mallee and Upper South-East, as well as in Victoria’s Wimmera, Mallee, Central and Northern Country districts. Entomologists have also received several unconfirmed reports that indicate the distribution of RWA may be wider than this. A current map of the confirmed distribution of RWA in Australia is available at the following link http://bit.ly/RWADist.
A RWA National Technical Group, comprising experts from across the country, has been set up by Plant Health Australia (PHA) 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 southern region grain growers to adopt a simple four-point plan in dealing with RWA.
GRDC Southern Manager Grower Services, Craig Ruchs, says 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,” Mr Ruchs said.
“Entomologists and other industry experts will closely monitor the RWA situation over 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.
The GRDC has produced an extensive Paddock Practices resource on RWA to inform grain growers’ management strategies.
More information and links to relevant resources are available at Plant Health Australia: http://www.planthealthaustralia.com.au/russian-wheat-aphid-management.
A GRDC Radio Southern Update interview with Craig Ruchs is available to listen to at the GRDC Radio (Southern Update) page.
* SARDI is a division of Primary Industries and Regions SA (PIRSA).
Greg Baker, SARDI
Paul Umina, cesar
03 9349 4723
Sharon Watt, Porter Novelli