BYDV tolerant varieties are risk reducers, not risk eliminators
Growers attending the Teagasc Crops Forum on September 10 heard that winter barley varieties tolerant to Barley Yellow Dwarf Virus (BYDV) should be viewed as risk reducers rather than risk eliminators.
That was a key message delivered by Dr. Louise McNamara, Entomologist at Teagasc, who addressed delegates at the gathering of farmers, researchers, specialists and industry representatives.
“There is great interest in tolerant and resistant varieties for the control of BYDV,” Dr. McNamara explained, “but it is only one tool; if you rely exclusively on one tool, it can potentially impact on the disease control plan.”
83% of the winter barley seed area under certification in Ireland in 2026 had tolerance or resistance to BYDV. Detailing validation trials ongoing at the Teagasc Crops Research Centre, Oak Park, Dr. McNamara highlighted that, many of these varieties would have been first tested in regions where the main species of the BYDV differs from that found in Ireland.
“We need to know are these tolerant varieties effective against the prevalent species in Ireland.”
In the Irish context, three species of BYDV were present in the trials, with BYDV-MAV being the most frequent, along with combinations of BYDV-MAV with BYDV-PAS and/or BYDV-PAV.
Trial results
To qualify this, Dr. McNamara shared results from six trials carried out over four years using susceptible (without tolerance) and tolerant varieties and insecticide sprayed versus unsprayed treatments.
In the unsprayed plots, the susceptible varieties clearly showed higher levels of BYDV symptoms than the tolerant varieties. However, the tolerant varieties did exhibit some BYDV symptoms, although these were markedly lower than those observed in the susceptible varieties. Insecticide spray programmes clearly reduced the level of BYDV symptoms in susceptible varieties. They also reduced symptom levels in the tolerant varieties, although these varieties had lower levels of BYDV symptoms from the outset.
Dr McNamara also used data from Teagasc research trials to compare the yield performance of tolerant and susceptible varieties in years with low, medium and high BYDV pressure.
At medium pressure, with a 5.2% YDV index, yield losses became apparent. Susceptible varieties showed a marked yield difference between sprayed and unsprayed plots, with all susceptible varieties significantly benefiting from insecticide treatment.
The tolerant varieties produced higher yields overall, but there was less difference between sprayed and unsprayed plots, indicating that they gained less additional benefit from insecticide treatment.
In a high-pressure year (YDV index of 17.3%), susceptible varieties showed a significant yield response to insecticide treatment, with a large difference in yield between sprayed and unsprayed plots. In contrast, there were no significant yield differences between sprayed and unsprayed plots for the tolerant winter barley varieties.
Concluding on this research, Dr. McNamara explained: “The average percentage of BYDV symptoms present across the years ranged from approximately 0% to 17% and the tolerant varieties reduced BYDV symptoms and associated yield losses.
“There were significant yield losses in susceptible varieties in four out of six of the trials and there was a significant yield loss in tolerant varieties in two out of six of the trials.
“Tolerant varieties still show BYDV symptoms, but susceptible varieties show increased BYDV symptoms and experience a more significant yield penalty when left unsprayed. Tolerant varieties are less likely to experience a yield penalty, but there may be some yield penalty in some years and conditions,” Dr. McNamara explained.
Dr. Louise McNamara featured on a recent episode of the Tillage Edge podcast, outlining recent trial results on controlling BYDV in BYDV tolerant varieties.
Listen in below: