Context. Yellow dwarf viruses (YDVs) form a complex of economically important pathogens that can significantly reduce grain yield in cereals. Mixed infections, or infection with two or more YDV species, can be particularly damaging.

Aims. We aimed to examine the proportion of single and multiple virus infections present in symptomatic cereal and grass plants in Victoria, south-eastern Australia.

Methods. Over 3 years (2020–2022), symptomatic cereal and grass plants from within and around cereal fields in Victoria, Australia were individually tested using tissue-blot immunoassay (TBIA) for barley yellow dwarf virus PAV, barley yellow dwarf virus MAV, cereal yellow dwarf virus RPV, wheat streak mosaic virus, and with a generic TBIA test that can detect multiple luteovirus and/or polerovirus species.

Key results. Across 2020–2021, 34% of virus-positive plants were infected with multiple YDV species. The proportion of mixed infections was similar in each individual year. However, higher proportions of wheat (Triticum aestivum, 47%) and wild oat (Avena fatua, 36%) plants were infected with multiple YDV species compared to barley (Hordeum vulgare, 8%) and brome grass (Bromus spp.,17%).

Conclusions. The proportion of virus-positive plants infected with multiple YDV species found was almost four times higher than previously reported in a similar study in Victoria, Australia in 1985. The proportion of plants infected with multiple YDV species varied more with host type than between individual years.

Implications. These findings demonstrate the complex epidemiology of these damaging viruses, and the challenges associated with developing virus-resistant cereal cultivars, while also highlighting the importance of regular surveillance over multiple years.