What is going on with Fall armyworm and Russian wheat aphid in Western Australia?

Key messages

Aims

To report the geographical range of two pests new to Western Australia (Fall armyworm and Russian wheat aphid) and provide management solutions to grain growers.

Introduction

Russian wheat aphid is found in all major grain growing countries where it is a pest of wheat and barley. The main concern regarding RWA is its potential to cause yield loss as unlike other aphids, RWA injects toxins into the plant during feeding that retard growth and lead to yield loss. Crops are most at risk from RWA feeding damage after GS30 (start of stem elongation) until GS50 (start of head emergence).

Method

Fall armyworm

Over 70 pheromone moth traps were established in the WA grainbelt to detect migration of fall armyworm from northern sources such as Carnarvon. The traps were a combination of manual bucket traps (Unitrap®) and automated moth traps (TrapView®) and monitored by DPIRD staff, grower groups and agronomists. Traps were monitored from June to October until crops senesced.

Russian wheat aphid

DPIRD initiated a Level 2 Incident in August 2020, which ran for three months. Field surveillance of wheat and barley crops was conducted by DPIRD staff, growers and agronomists to establish the geographical distribution of RWA.

Results

Fall armyworm surveillance

Although fall armyworm moths were detected at Geraldton and Gingin in 2020, no moths or larvae were detected at grainbelt sites or from public reports of caterpillars via samples or images. Trap sites are presented in Figure. 1. At present, Carnarvon is the most southern point where fall armyworm caterpillars have been confirmed.

Figure 1. Manual and automated (TrapView®) fall armyworm moth trapping sites in the WA grainbelt during 2020.

Russian wheat aphid surveillance

A total of 121 sites were surveyed throughout the grainbelt, however RWA was found in 24 sites in the Esperance port zone only (Figure 2). Sites with RWA were located in low, medium and high rainfall areas. RWA was found on early and late-sown barley and wheat crops. Surveys found notably fewer RWA in crops that had an insecticide seed dressing. RWA was present at levels of less than 1% of tillers with RWA, which is well below control thresholds (see GRDC 2020).

Figure 2: Localities of surveillance for Russian Wheat Aphid and its presence/absence status

Conclusion

Fall armyworm and Russian wheat aphid are new pests of grain, pasture and horticulture crops in WA. Proper identification, surveillance and an integrated pest management approach will be key in managing these pests going forward.

Although fall armyworm larvae have not been detected in crops or pastures in the WA grainbelt, growers should be vigilant and report suspect caterpillars given their migratory ability over large distances in short periods of time. Identification and management advice (including permitted insecticides for grain crops) can be found at the DPIRD fall armyworm web page: www.agric.wa.gov.au/n/8110.

Although RWA was not found outside of Esperance during 2020, it is highly probable that this pest will migrate from the Esperance port zone. Climatic modelling conducted by Avila et al(2018) predicts that RWA has the potential to persist in all broadacre growing areas of WA. In South Australia, RWA can survive hot dry summers on perennial grasses (Kirkland et al 2019), and higher numbers are found in areas that have had a green bridge for more than eight weeks (van Helden 2021). In WA, surveillance is planned for 2021 to determine the persistence of RWA in Esperance and its presence in the WA grainbelt.

Acknowledgments

The authors wish to thank the growers, grower groups and agronomists that assisted with RWA surveillance and moth trap surveillance (West Midlands Group, Liebe Group, Mingenew Irwin Group, South Eastern Agronomy Services). Thanks to DPIRD staff Christiaan Valentine, Amber Balfour-Cunningham, Andrea Hills, Joel Kidd and Brent Ladyman for moth trap surveillance. Helen Spafford (DPIRD Kununurra) leads the DPIRD fall armyworm response within DPIRD.

References

Archer TL and Bynum EO (1992). Economic Injury Level for the Russian Wheat Aphid (Homoptera: Aphididae) on Dryland Winter Wheat. J Econ Entomol 85:987–992. doi: 10.1093/jee/85.3.987

Avila GA, Davidson M, van Helden M and Fagan L (2019). The potential distribution of the Russian wheat aphid (Diuraphis noxia): an updated distribution model including irrigation improves model fit for predicting potential spread. Bulletin of Entomological Research 109, 90–101.  doi: 10.1017/S0007485318000226

GRDC (2020) Russian Wheat Aphid. Available at: https://grdc.com.au/resources-and-publications/resources/russian-wheat-aphid

Kirkland L, Pirtle E, Maino J, Severi J, Lye J, Umina P, Heddle T and van Helden M (2019) Russian wheat aphid - current investigations and recent findings, GRDC Research Update papers  https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2019/02/russian-wheat-aphid-current-investigations-and-recent-findings

van Helden M, Heddle T, Pirtle E, Lye J ,Maino J (2021) Russian wheat aphid thresholds - Insect density, yield impact and control decision making, GRDC Research Update papers

Contact details

Dusty Severtson,
Department of Primary Industries and Regional Development
75 York Rd, Northam WA 6401
08 9690 2160
dustin.severtson@dpird.wa.gov.au

Svetlana Micic
Department of Primary Industries and Regional Development
444 Albany Why, Albany, WA 6330
08 9892 8591
svetlana.micic@dpird.wa.gov.au