Managing what might bug you this season

Take home messages

  • Our research update provides information and management solutions for growers and advisors on key grains pests which may cause issues this year.
  • In 2022, the mild wet weather is likely to increase green bridge risk which can allow some pests to persist over summer and become problems for establishing crops.
  • Increasing insecticide resistance is an important consideration for pest management decisions in grain growing regions this year.
  • We discuss research updates and management for pests, including Russian wheat aphid (RWA), green peach aphid (GPA) and redlegged earth mite (RLEM).
  • Tools and services available to help manage pests include resistance testing for RLEM and GPA; a threshold calculator for the RWA; and a hatch timing tool and severity risk calculator for RLEM.


The ability to efficiently respond to insect pest threats will be paramount to the Australian grains industry in 2022. One of the most important considerations for the grains industry is the increasing need to improve the way insecticides are used in order to reduce the evolution of resistance and protect beneficials. Integrated pest management (IPM) provides guidance on sustainable practice and is most effective when management actions are supported by the understanding of local conditions, on-the-ground information about pest biology, and access to effective alternatives to pesticide use. In this presentation we will:

  • provide information on how key grain pests are likely to respond to conditions in 2022
  • explore management considerations in response to rising insecticide resistance
  • provide information on tools and services that may help growers and advisors stay on top of pest problems this year.

Climate outlook and green bridge risk in 2022

Insect pests are often seasonal, and each species' potential impact on farming systems is influenced by a range of environmental factors. Similar to the conditions seen last year, we are likely to have a mild, wet summer in 2022. The recent switch to La Niña in the Asia Pacific region has meant very wet summers compared to the years prior. Data from the Bureau of Meteorology predicts that rainfall from January to March is likely to be above median for east coast NSW, eastern Victoria and areas near the NSW-Victoria border. Rainfall and temperatures for Victoria and southern NSW from March to May are not expected to vary significantly from the average. Wet conditions are likely to support above average crop and pasture production through summer. However, it may also have substantial implications for the emergence and persistence of pests. A wetter than average summer means that much of the vegetation that would normally dry out, die off or fail to germinate may flourish throughout the warmer months, providing the opportunity for a so-called ‘green bridge’ to grow between winter cropping seasons. The green bridge is plant material, crop volunteers and weeds growing between cropping seasons, that creates habitat for pests and diseases to persist and thrive. These out-of-season plants allow pests to move from one season’s crop to the next, which can be especially damaging to establishing winter grains crops at the early growth stages. Although green bridges can provide good conditions for beneficials early in the season, they can also be reservoirs of crop diseases and are host to many key pests such as slugs, snails, the diamondback moth, and a range of aphids, including the RWA and the GPA.

Insecticide resistance in Australia

Insecticide resistance is a growing problem for the Australian grains industry. Reliance on a select number of chemical options for management of key insect grain pests has created strong selection pressure that drives the evolution of resistance. Resistance reduces the number of effective insecticide options available and places additional selection pressure on the remaining chemical actives as growers begin to utilise these alternative insecticides more regularly. Modelling work, undertaken by Cesar Australia as part of a GRDC integrated pest management investment for the southern region, has identified specific pests at high risk of evolving future resistances. Pests on this list include species that are already known to exhibit resistance, as well as additional key grain pests that currently are not known to be resistant. The evolution of further resistance in grain insect pests could prove both costly and complex for growers’ pest management regimes (Maino et al. 2018a). Importantly, a substantial amount of research on insecticide resistance in key grain pests has been undertaken in the last few years and resources have been developed to help grain growers and advisors manage the risks of resistance. Currently, four major grain pests are known to have widespread resistance to multiple insecticides: cotton bollworm (Helicoverpa armigera), diamondback moth (Plutella xylostella), green peach aphid (Myzus persicae, GPA) and redlegged earth mite (Halotydeus destructor, RLEM). Several other minor grain pests, including silverleaf whitefly (Bemisia tabaci), two spotted mite (Tetranychus urticae), western flower thrips (Frankliniella occidentalis) and onion thrips (Thrips tabaci), have also recorded resistance to insecticides in Australia. Here, we present recent findings relating to the current status of insecticide resistance in GPA and RLEM, including the development of resistance management strategies for these species.

Results and discussion

The green bridge risk and Russian wheat aphid

For most grain growing regions in Australia, Russian wheat aphid (RWA) populations grow within cultivated crops over the winter, disperse into ‘over-summer’ refuges, and then re-disperse back into emerging crops during an autumn migration. Crop damage occurs when RWA migrate into crops during establishment in high numbers. Conditions in the previous growing season and the intervening summer determine the risk of establishment at crop emergence. Russian wheat aphids cause problems when conditions during the previous spring support successful migration from mature cereal crops onto summer hosts and when over summer conditions allow populations to survive in high numbers. Conditions during autumn will also affect the ability of the RWA to migrate into emerging crops, especially if an early break will create a growth flush of its main host, barley grass (van Helden et al. 2021). Importantly, RWA persistence in green bridges is associated with moderate temperatures of below 20ᵒC, low to moderate available soil moisture (5% in top 0-10cm), with migration occurring when daily maximum temperatures exceed 24°C (Ma and Bechinski 2009). It is important to note, however, that a higher presence of RWA in some green bridge areas does not necessarily mean they will move into crops. Yet, the higher refuge risk does serve as a timely reminder to plan green bridge management and to monitor establishing crops for movement of RWA into paddocks.

Russian wheat aphid management

The ability of RWA to migrate and cause damage is strongly influenced by the green bridge, therefore ongoing control includes eliminating refuge volunteer cereals and grasses in fallows and other areas before sowing. Prophylactic seed treatments are rarely justified. Later planting of winter cereals can delay and reduce early infestations, and agronomic practices to promote crop vigour and dense canopy growth can help to inhibit RWA populations and reduce their impacts. In some circumstances, chemical control may be required. Researchers from SARDI and Cesar Australia have developed a calculator to assist growers and advisors to decide whether spraying for RWA is economically justified (van Helden et al. 2022). This action threshold calculator considers dynamic factors, including the cost of control, cereal market price and aphid numbers. It can be used between GS30 (start of stem elongation) and GS50 (start of head emergence), although monitoring is recommended at GS30. This calculator is the culmination of field trial data collection and analysis over two winter cropping seasons (2018-2019) in south-eastern Australia.

Predicting redlegged earth mite hatch dates and severity risk

The RLEM is another pest common in Australian grain growing regions that is strongly influenced by climatic conditions. Redlegged earth mites enter diapause over summer, emerging as the weather becomes more favourable. Early-season management, therefore, relies strongly on the timing of hatching of summer diapause eggs. Previous research indicates that RLEM eggs in south-eastern Australia hatch after 5mm of rain over 5 days, followed by 10 days of mean temperatures below 16°C (McDonald et al. 2015). This knowledge has allowed us to use weather data (maximum/minimum temperatures and rainfall) to predict when RLEM populations will hatch in different regions each season. Most of Victoria and southern NSW would normally expect to see egg-hatch starting in mid-April. However, with a wet and cooler than average start to the season in many regions, the RLEM prediction models are showing earlier than average hatching dates. A cool start to the season could also create a false break, causing RLEM eggs to hatch but fail to develop, if conditions do not continue to be suitable (for example, in a warm, dry autumn or if there is not adequate food available). The RLEM hatch timing tool has been developed through a GRDC investment (CES2010-001RXT) with contributions from CSIRO, Cesar Australia, the University of Melbourne, and the Department of Primary Industries and Regional Development (DPIRD) to estimate the timing of egg hatch in different locations depending on local climate conditions. The hatch timing tool assists decision making by predicting when eggs will hatch in autumn, which is a key indicator of when to increase crop monitoring.

Best management practice of RLEM involves using Timerite® in the previous season to limit the number of diapause eggs produced in spring. If it is suspected that RLEM may become a problem, growers and advisors can use the severity risk assessment tool featured in the ‘Redlegged earth mite: best management practice guide’, created by Cesar Australia, Birchip Cropping Group and SARDI. Several factors need to be taken into consideration when using this tool to predict whether the RLEM may become a problem in a paddock, including:

  • the type of crop last year
  • the type of crop this year
  • the extent of broadleaf weed cover in the paddock
  • the presence of the species in previous years
  • the spray history of the paddock.

A series of questions in the risk assessment tool can be used to assist growers and advisors in weighing up these factors to calculate a ‘RLEM risk-rating’ for individual paddocks. Recently, through the project ‘Future options for the control of RLEM in Australian grain crops’ (CES2010-001RTX), the project team has developed an online, interactive risk calculator based on this best practice guide.

Redlegged earth mite insecticide resistance

Control of RLEM is largely reliant on three registered chemical classes: neonicotinoids (as seed dressings), synthetic pyrethroids (SPs), and organophosphates (OPs; as foliar insecticides). Continued use of this limited set of agrochemical options in Australia has resulted in resistance issues (Umina 2007, Arthur et al. 2021). Redlegged earth mite populations resistant to either SPs or OPs, or both, are now present across large areas of Western Australia and parts of eastern Australia. This includes confirmed resistance in multiple populations from South Australia in 2017 and a recent detection in Victoria (Maino et al. 2018b). Cesar Australia is offering a screening service to test for RLEM insecticide resistance within South Australia, Victoria, NSW and Tasmania. The screening is at no-cost for Australian grain growers and advisors, thanks to GRDCinvestment. We are particularly interested in hearing from growers and advisors who have either experienced recent or past chemical control failures or have paddocks that are frequently impacted by RLEM and have required spraying. This service is playing a key role in detecting resistance before it becomes widespread and is assisting in the identification of best control options for growers. During the 2022 season, we will be undertaking field collections of RLEM for resistance screening, so please get in touch if you would like us to collect RLEM from your area.

Insecticide resistance in green peach aphid

The green peach aphid (GPA) is a widespread pest across Australia and is common in many broadacre crops, broadleaf pastures, and horticultural crops. Insecticide resistance in GPA is a major threat to canola and pulse production in Australia. There are diminishing chemical options available to growers, and the functional diversity, prevalence, and severity of resistances encountered in the field is increasing. Importantly, GPA can transmit over 100 plant viruses, which drives many of the insecticide applications targeted at this pest. While resistance issues and regulatory pressures are removing older chemistries from use, new mode of action chemistries — which are increasingly costly to develop, register and apply, and slow to market — are also at risk. This is evidenced by the recent finding of sulfoxaflor resistance evolving in parts of Western Australia. As part of a previous GRDC investment (CES00003), we developed bioassay methodologies and generated baselines for GPA to sulfoxaflor. This allowed us to efficiently investigate the chemical control failures experienced in Western Australia and thus inform industry in a matter of a few weeks (as opposed to six months or more). Current GRDC investment (CES2001-001RTX) is undertaking research to track resistance evolution and map distributions of insecticide resistances in GPA populations across Australia. The project aims to characterise seasonal and regional patterns between GPA host preference, GPA migration, insecticide resistant GPA, and turnip yellows virus dispersal. We will also develop baseline sensitivity data for new chemicals and update the GPA Insecticide Resistance Management Strategy (IRMS) in line with new research. Updating the IRMS will enable more effective management of GPA and support more sustainable use of chemical options. As for RLEM, Cesar Australia also offers a resistance testing service for GPA. We would like to strongly encourage grain growers and advisors across Australia to report any observations of potential insecticide failures.

Green peach aphid and TuYV transmission

Turnip yellows virus (TuYV; formerly known as beet western yellows virus) is primarily spread by the GPA, which has a very high (96%) transmission efficiency. Once acquired, the virus is carried within the aphid for its entire lifecycle and transmitted to healthy plants during feeding. TuYV is difficult to manage because chemical treatments do not work post-infection, as they do with fungal diseases. Therefore, prevention of infection via monitoring and control of GPA is the best defence. Mild temperatures in March and April provide optimal conditions for GPA to multiply and potentially spread TuYV from volunteer canola and brassica weeds to this season’s crops. The virus is also thought to be more prevalent in wetter than average years because of the increased risk of aphids entering seedling crops from green bridges. Therefore, growers and advisors will need to be aware of GPA in 2022, especially considering the insecticide resistance issues discussed above.

A proactive approach to manage GPA is essential for limiting the impact of TuYV. DPIRD and Cesar Australia are currently testing an early warning system to support proactive management of TuYV epidemics in Australian canola crops. As part of the program, agronomists throughout Western Australia, Victoria and southern NSW deploy sticky traps which are regularly sent to DPIRD where captured aphids are tested for TuYV using a rapid and sensitive RNA detection technique. The project also includes leaf sampling when the canola crop is at GS30 (stem elongation) to assess levels of virus infection. The project deployed sticky traps at 16 locations in Victoria and southern NSW in 2021 (Figure 1). A high prevalence of the virus was detected in aphids caught on sticky traps in 2021, with large numbers of aphids (including GPA) caught, and TuYV detected in the crop at 10 of the 16 sites tested (1% to 86% infection). In 2020, TuYV was detected at all 13 locations tested (1% to 58% infection).

Figure 1. Site location and density by month of turnip yellows virus and GPA detected across 16 sites in Victoria in 2021.

Figure 1. Site location and density by month of turnip yellows virus and GPA detected across 16 sites in Victoria in 2021.

Insecticide resistance management

Insecticide resistance management strategies have been developed for the four main resistant grain pests as well as a number of best management practice guides that provide information on applying integrated pest management practices in the field, including for cotton bollworm, diamondback moth, GPA and RLEM. To give growers and advisors easy access to up-to-date and relevant information, we are developing a new online platform called AgPest (being developed under AGPIP). This website will provide a central portal through which existing resources can be accessed as well as provide access to new decision-aid tools for management of insecticide resistance in grains. The platform will host up-to-date information on known resistant pests, maps that display known resistances across Australia, resources on beneficial insect stewardship (including information on insecticide toxicities for different natural enemy species) and access to resistance management resources.


Some important factors to be considered heading into 2022 are the green bridge harbouring pests over summer and the rising levels of insecticide resistance in key crop pests. The use of timely monitoring and pro-active management of risk factors can help to keep pests below threshold levels and reduce the need for extensive chemical control. If you need to identify pests or suspect resistance in any of the at-risk pests mentioned above, you can contact the Cesar Australia PestFacts south-eastern team for more information.


The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the authors would like to thank them for their continued support. The TuYV work was funded by DPIRD Boosting Grains Science Partnerships project 2019SP02. AGPIP is a collaboration between the Pest & Environmental Adaptation Research Group at the University of Melbourne and Cesar Australia. The program is a co-investment by the Grains Research and Development Corporation (GRDC) and the University of Melbourne, together with in-kind contributions from all program partners. We also thank all of our project partners including South Australian Research and Development Institute (SARDI), Department of Primary Industries Research and Development (DPIRD), Queensland department of agriculture and fisheries (QDAF) and NSW department of primary industries (NSW DPI).


Arthur AL, Maino J, Hoffmann AA, Jasper M, Lord A, Micic S, Edwards O, van Rooyen A, Umina PA (2021) Learnings from over a decade of increasing pesticide resistance in the redlegged earth mite, Halotydeus destructor (Tucker). Pest Management Science 77(6), 3013–3024.

Ma Z, Bechinski EJ (2009) Life tables and demographic statistics of Russian wheat aphid (Hemiptera: Aphididae) reared at different temperatures and on different host plant growth stages. European Journal of Entomology 106(2), 205–210.

Maino JL, Binns M, Umina P (2018b) No longer a west-side story - pesticide resistance discovered in the eastern range of a major Australian crop pest, Halotydeus destructor (Acari: Penthaleidae). Crop and Pasture Science 69(2), 216–221.

Maino JL, Umina PA, Hoffmann AA (2018a) Climate contributes to the evolution of pesticide resistance. Global Ecology and Biogeography 27(2), 223–232.

McDonald G, Umina PA, Macfadyen S, Mangano P, Hoffmann AA (2015) Predicting the timing of first generation egg hatch for the pest redlegged earth mite Halotydeus destructor (Acari: Penthaleidae). Experimental and Applied Acarology 65, 259–276.

Umina PA (2007) Pyrethroid resistance discovered in a major agricultural pest in southern Australia: the redlegged earth mite Halotydeus destructor (Acari: Penthaleidae). Pest Management Science 63(12), 1185–1190.

Van Helden M, Heddle T, Proctor C, Alhwash L, Wake B, Al-Jawahiri F (2021) Noncrop host plant associations for oversummering of Diuraphis noxia in the State of South Australia. Journal of Economic Entomology 114(6), 2336–2345.

Van Helden M, Heddle T, Umina PA, Maino JL (2022) Economic injury levels and dynamic action thresholds for Diuraphis noxia (Hemiptera: Aphididae) in Australian cereal crops. Journal of Economic Entomology: in press.

Pest Facts south-eastern

How well will Russian wheat aphid cross the green bridge this season?

Redlegged earth mite best management practice guide – Southern 

Redlegged earth mite hatch timing tool

Redlegged earth mite seasonal risk estimate (draft version)

Turnip yellows virus early warning system

Insecticide resistance in the southern region: current status, future risk and best management practices

Contact details

Dr Paul Umina
Level 1, 95 Albert St, Brunswick Victoria 3056
03 9349 4723

GRDC Project Code: CES1904-002RTX, UOM1906-002RTX, CES2001-001RTX, CES2010-001RXT, CES1506-001RTX, UOA1805-018RTX,