Does barley yellow dwarf virus pose a threat to my crops?

Barley yellow dwarf virus (BYDV) is a real talking point for tillage farmers this year, particularly those involved in feed and malting barley production.

It’s spread by the grain aphid and an outbreak can impact greatly on the yield of barley crops. In some scenarios, it can result in yield losses of up to 40%.

To answer some of the questions farmers may have on this costly virus, Teagasc’s Dr. Louise McNamara presented the latest research findings at yesterday’s Crops and Cultivation open day in Teagasc Oak Park.

What are the risk factors for BYDV?

McNamara, Teagasc Research Officer, touched on some of the key risk factors associated with BYDV, many of which centre around sowing date.

On autumn-sown cereals, McNamara said: “Early-sown autumn cereals and late-sown spring cereals are at most risk from the virus.

“Mild winters also increase the risk, as the number of aphids surviving over the winter increases. Mild autumn weather also increases the risk because the aphids’ migration period lengthens, so the conditions may be more favourable for aphid flight for longer.”

Control – autumn crops

For early-sown autumn cereals, McNamara said farmers should consider a control programme; this could include the use of treated seed and a single application of an aphicide or two applications of an aphicide (one at the two-to-three week stage and the other in the first week of November).

For October-sown cereals, the risk is medium-to-high so you may need a seed treatment or aphicide application in the first week of November.

“For crops emerging after November, the risk of BYDV is seen to be lower so control may not be needed unless it is a very mild winter where aphid numbers are very high or you are in a high-risk area,” she added.

Control – spring crops

Moving on to spring-sown crops, the Teagasc representative said: “March-sown cereals are seen to be at a lower risk and an aphicide spray may not be necessary.

“For April-sown crops, the risk is medium-to-high and an aphicide application may be needed at the four-leaf stage,” she said.

Teagasc trial work

McNamara also touched on research work carried out in the counties of Cork and Carlow, which looked at the occurrence of BYDV is winter-sown crops.

39% of the untreated plots in Co. Cork had shown signs of BYDV, she said, but this dropped to 11% and 3% for crops treated with a single spray of pyrethroid and seed-treated plots respectively.

Moving to trial plots in Co. Carlow, she said: “The overall disease pressure was lower, with the untreated crops having 4% of all tillers affected, and 2% of the tillers in the pyrethroid-treated and seed-treated plots having visible symptoms of BYDV.

This shows the difference in the disease pressure in different areas and how the advice may need to be tailored depending on where the crop is located.

Resistance detected

Despite the control programmes outlined above, McNamara also touched on a worrying issue relating to the control of aphids; this is knock down resistance (KDR) to pyrethroids.

“To date, knock down resistance has only been detected in the grain aphid and this has been found to be the most prevalent cereal aphid in cereal crops in Ireland.

“It’s important to note that there are other aphids present in your crops. The research indicates that the aphids carrying the resistance genes are found in all major grain-growing regions in Ireland.

“The work in this area is ongoing and we need to do more to understand the implications of this resistance gene for the future,” she concluded.

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