Managing Subterranean Clover Red Leaf Syndrome in Western Australia Stage 1

Summary

​There has been concern amongst livestock producers regarding recent outbreaks of subterranean clover red leaf syndrome of which the most likely primary cause is infection by the Soybean dwarf virus (SbDV). To improve our understanding of the epidemiology of SbDV we undertook an autumn sampling program in 2018 to determine which plant species harbour SbDV between growing seasons. A total of 6749 live plant samples were collected and tested from 22 locations. SbDV was only found at one of the locations in strawberry (Trifolium fragiferum L.) and white clover (T. repens). Migrating aphids, which are the vector for the virus, were not found at any of the sites where sticky traps were deployed. Based on these results and previous investigations, if an outbreak occurs this year (2018) it is likely to be in spring when aphid populations build up. Further research under controlled glasshouse conditions is required to determine if common broadleaf weeds, and native and exotic Fabaceae plant species are either over summer or growing season hosts of SbDV.

In addition to the autumn 2018 survey, aphids trapped in 2017 were tested for SbDV and found to regularly have the SbDV virus particularly in September suggesting that virus is relatively common in aphids in spring.

The subterranean clover red leaf syndrome factsheet has been completed and is currently being disseminated to the livestock and seed industry. Monitoring of pastures for the syndrome will continue throughout the 2018 growing season.

There are still significant gaps in our understanding of the subterranean clover red leaf syndrome. We recommend that future research focuses on the tolerance of legume species and cultivars to the virus, identifying the over summer hosts of SbDV is a priority and the development of disease management tools.