The Russian wheat aphid. Symptoms of damage include leaf streaks and rolling of leaves.
Photo courtesy of Michael Nash, South Australian Research and Development Institute (SARDI), a division of Primary Industries and Regions SA (PIRSA).
The Grains Research and Development Corporation (GRDC) is encouraging Southern region grain growers to adopt a simple four-point plan in dealing with Russian wheat aphid (RWA).
As the GRDC implements a multi-faceted research, development and extension approach to better inform future control of the pest – detected in Australia for the first time last month – growers are reminded to continue to scout fields and implement a considered management strategy.
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 and potential yield losses)
- Enact an appropriate management strategy that where possible encourages beneficial insects.
Craig Ruchs, GRDC Southern Manager Grower Services, says with RWA now established in South Australia and Victoria, the focus has moved from eradication to development and implementation of an appropriate long-term management strategy.
“Because this pest is new to Australia, there are still many unknowns in terms of basic population dynamics, developmental and reproductive processes and triggers for long distance movement under local conditions,” Mr Ruchs said.
“Growers can rest assured that the GRDC, its research partners and other agencies are working hard to develop an improved understanding of how this pest behaves, its impact and suitable approaches to management under our environment and cropping systems,” Mr Ruchs said.
“The GRDC is making a significant investment in a range of research, development and extension activities that will enable development of an integrated management approach and quickly fill the gaps in our current understanding of pest biology, population dynamics and specific control options.
“The immediate priority is to generate an improved understanding of the relative effectiveness of those insecticides currently registered for control of other aphid species in Australian cereals. While an Australian Pesticides and Veterinary Medicines Authority (APVMA) permit currently exists for the use of chlorpyrifos and pirimicarb (APVMA 82792), we need to compare these active ingredients with other chemistry including neonicotinoid and synthetic pyrethroid insecticides.”
Mr Ruchs said in addition, the economic thresholds for control have not yet been validated locally and this was an urgent need in order to provide increased confidence in grower decision making around when to spray.
“Whilst we do have indicative thresholds to guide growers based on existing international literature it is important to understand that the economic threshold for control will vary by situation. Potential yield loss in our environment, crop yield potential and cost of the chosen control measure must always be considered,” explained Mr Ruchs.
“The good news is that GRDC has previously invested in pre-emptive pre-breeding activities associated with varietal resistance to this pest in a partnership led by Murdoch University and involving national and international collaborators. While no resistance to RWA was identified in a screen of major Australian wheat and barley cultivars several years ago, encouragingly the project did develop some material where resistance genes were introgressed into Australian cereal backgrounds,” Mr Ruchs said.
The GRDC continues to work with research partners and plant breeding companies in Australia to make germplasm available for commercial breeding.
Mr Ruchs said that in the meantime, it was important that growers and their advisers continue to scout crops and where RWA is identified to speak with their local adviser or district agronomist in relation to an appropriate control strategy.
“It’s a similar situation to that of any other insect pest in crops; assess what the level of infestation is and determine if/what treatment is necessary.
“The FITE strategy is a simple way to assist growers in the decision-making process: Firstly, scout cereal crops and grasses and if you Find typical symptoms of damage (such as leaf streaks and rolling of leaves) then the second step is to positively Identify the aphid species present – consult your local adviser if unsure.
“The third step is to consider economic Thresholds for control before getting the sprayer filled and ready to go. International advice supports an economic threshold of 20% of plants infested up to the start of tillering and 10% of plants infested thereafter. It is important, however, to understand that these thresholds have yet to be validated under Australian conditions. The main point here is to avoid prophylactic sprays where the pest is either not present or is present in very low numbers within a field.
“The fourth step is Enacting an appropriate management strategy; one that factors in the importance of encouraging beneficial insects which may act as natural predators, as well as the potential impact on honeybees.”
Mr Ruchs said if assessments of crop damage and economic threshold levels determine that treatment is necessary, growers could consider applying chlorpyrifos 500 at 600ml/ha or pirimicarb 500 at 250g/ha under an APVMA emergency use permit.
Victorian growers may also consider the application of omethoate or dimethoate at registered use rates in cereal crops.
“While work is underway to compare a broader range of insecticide options for control, current recommendations are based on limited local evaluation,” stressed Mr Ruchs.
“Current information from overseas suggests that the effectiveness of synthetic pyrethroid insecticides may differ by product and more work is required to validate this locally. Key considerations when spraying are spray quality and volume, adjuvant selection and product choice.
“The vapor activity of some insecticides is influenced by temperature, so it is important to consider the appropriate practice for each specific situation, weather conditions and product to be used. As the pest may harbour in rolled leaves or leaf axils, direct contact may be more challenging than for some other aphid species.”
Growers and advisers will be kept informed as more information comes to hand but are reminded to always refer to the product label and adhere to local and State legislation relating to pesticide use.
Growers and advisers are still encouraged to report suspected sightings of RWA to the Exotic Plant Pest Hotline (1800 084 881).
Primary Industries and Regions SA – Russian wheat aphid information (including fact sheets):
PestFacts newsletters – Russian wheat aphid in South Australia:
PestFacts newsletter – Russian wheat aphid in Victoria:
Plant Health Australia: http://www.planthealthaustralia.com.au/
GRDC website: www.grdc.com.au
Biosecurity SA plant health enquiries (08) 8207 7820
Exotic Plant Pest Hotline (1800 084 881).
Craig Ruchs, GRDC
Phone 0477 710813
Sharon Watt, Porter Novelli
Phone 0409 675100