Aphids and virus transmission: what’s the risk?

It’s been a dry autumn in many regions of Victoria and NSW; a lack of moisture is likely to impact aphid numbers.

 

While there are multiple factors that contribute to pest and disease outbreaks, seasonal weather conditions are one of the driving factors.

Take for example, the 2014 outbreak of Turnip yellows virus, TuYV (syn. Beet western yellows virus) in canola, in areas of south-eastern Australia. Rainfall was ‘above average’ to ‘very much above average’ across large areas of Victora and southern NSW (Figure 1, left) between Feburary and April. This resulted in a ‘green bridge’ of weed hosts of TuYV, which supported incubation of the virus and populations of its primary vector, the green peach aphid (Myzus persicae, GPA).

Now looking to 2018, rainfall has been ‘below average’ to ‘very much below average’ for many regions of Victoria and southern NSW between Feburary and April (Figure 1, right), and this may have implications for aphid numbers in establishing crops.

The lack of moisture in many regions will have limited the potential for growth of weeds and volunteers over autumn. The knock on effect of this is a less accommodating environment that would otherwise foster growth of aphids and virus activity. That is, less ‘green brige’ around at a time that typically coincides with autumn migration of aphids.

A second driver behind the 2014 TuYV outbreak, was the warmer than average temperatures during autumn and early winter, which encouraged prolonged aphid activity.

However, while we have experienced mild weather during much of autumn this year, it’s likely that the lack of moisture and plant growth will have restricted aphid activity and the potential reservoir of viruses overall.

 

Figure 1. South-eastern Australian rainfall deciles, 1 Feburary to 30 April, during 2014 (left) and 2018 (right) (Source: Australian Bureau of Meteorology).