The second session of the Teagasc National Tillage Conference took place last week and provided an update on some of the different research projects taking place.

It began with a very interesting update on the Teagasc aphid monitoring network by Louise McNamara and Stephen Bryne, which provided information on the number of aphids in flight during the season and the proportion carrying virus and/or partial pyrethroid resistance.

At last year’s conference, we learned that there were very few aphids flying through April and most of May at Oak Park in 2020.

Numbers began to pick up from the end of May onwards, when temperatures got up above 11°C.

The Grain Aphid (Sitobion avenae) had a relatively short movement window from the end of April to mid-August, (this is thought to be the main BYDV vector) but the Bird Cherry Oat Aphid (Rhopalosiphum padi) was flying out to the end of November.

Virus and resistance monitoring

Last week, Louise McNamara presented the 2021 results for Oak Park and Cork. As well as the numbers of different aphids flying, she presented the number of Grain Aphids found to be carrying the BYDV virus and/or Kdr resistance.

From this, it is interesting to note that most of the flying aphids captured in the suction tower were not carrying BYDV, especially when the total numbers flying were highest. Indeed, with no Grain Aphids found to be flying after week 34, we now need to know if the virus will be transmitted by other species.

In this same timeframe, the incidence of Kdr-positive aphids found was generally low and only a very small proportion of aphids carried both virus and resistance.

Louise noted that Grain Aphid numbers at Oak Park in 2021 were six times higher than in 2020. This would suggest a high potential to infect autumn-sown crops, but whether the risk of BYDV infection could still be limited by the number of those aphids carrying the virus is currently unknown.

Ultimately, we need field trials alongside the monitoring to see how levels of virus-carrying aphids in the traps impact on disease pressure in the field. Testing showed that the number of those aphids carrying BYDV in 2021 was 50% lower than in 2020.

Results from the Cork tower in 2021 were broadly similar, but numbers were much lower.

At this site, the Bird Cherry Oat Aphid was the main BYDV-vectoring species captured during July and August (there were some Grain Aphids also), but numbers decreased from the end of August. Winged Bird Cherry Oat Aphids were still captured into December.

Further examination of these aphids found that the majority were negative for both BYDV presence and Kdr resistance. However, at weeks 32, 33 and 36, 33% to 100% of the aphids captured were positive for the presence of BYDV.

Between weeks 27 and 33, the level of Kdr resistance found varied between 0% and 29% of the aphids captured in that tower.

Flight factors

Further examination of the results on Grain Aphids found that the number of winged aphids increased considerably when temperatures rose above 11-15°C, but rain had a negative effect on aphid numbers flying, even when temperatures were high. However, the impact of rain at higher temperatures is not absolute.

Wind speed was also found to affect the number of Grain Aphids flying, with none found when wind speed was 0-5km/hr.

The majority were captured when wind speed was between 5-10km/hr. The findings show that the majority of aphids were captured at between 5-10km/hr when temperatures were 15-20°C.

Going forward

For 2022, a third tower joins the monitoring network and research will be ongoing to examine the relationship between the results found in the towers and the presence and incidence of BYDV in fields around the country.

The overall objective is to test the validity of the results from the towers against what is happening in fields and to use this information to produce a decision support system for farmers that would link into an integrated pest management system to guide farmer decisions on BYDV prevention.

Future work will also identify the strains of the virus found in the aphids.