Beware of another ‘perfect storm’ for BYDV

Spring cereals across much of the UK could again be at high risk from Barley Yellow Dwarf Virus (BYDV) infection, agronomy firm Hutchinsons warns.

Late drilling due to poor weather during March and April means many crops are much less advanced than normal, so could be more susceptible to winged aphid attack over coming weeks.

Latest monitoring by AHDB and Rothamsted suggests aphid activity remains low, but field reports suggest aphids have started flying and the situation can quickly change, as many growers witnessed last year, Hutchinsons technical support manager Duncan Connabeer says.

“Last spring was a perfect storm for BYDV, when a huge aphid flight coincided with the emergence of late-sown spring cereals. This resulted in significant BYDV symptoms in various regions, including places where it’s not normally an issue, such as parts of northern England, southern Scotland and the north Midlands.

“This season could again play into the hands of aphids if we see numbers increase.”

Although aphid-borne BYDV is typically less of a threat in northern parts of the UK compared with the south, Cumbria-based Hutchinsons agronomist Helen Brown says it was a problem in some crops last spring and she fears a repeat this year.

“Aphid arrival tends to be much later in the north and last year we found it coincided with the emergence of spring cereals. The same could happen this year given the delays to drilling.”

Miss Brown is leading research into possible varietal differences in BYDV incidence at the Hutchinsons Regional Technology Centre near Carlisle (see below).

Evaluating risk

Spring barley is most susceptible to aphids when plants are young, typically up to growth stage 31, after which time crops can usually outgrow infection.

Early is therefore better than late if growers insist on treating crops with an aphicide, but Mr Connabeer warns that any spraying for aphids in spring is unlikely to be effective given rapid crop growth and repeated aphid flights.

Rapid growth of spring barley can soon dilute active ingredients, which may also be broken down faster by high UV light levels, reducing their efficacy, he notes. Also, crops can often soon grow past the stage where virus causes any significant yield impact, despite visual symptoms being visible. This is unlike winter cereals where the yield impact from BYDV can be much greater.

Duncan Conabeer.

Hutchinsons trials at some sites last year showed multiple pyrethroid applications to spring cereals had no impact on visual crop yellowing caused by BYDV. Even in bad years such as 2017, there is limited evidence to show a significant yield impact from BYDV, and in many areas aphids are a threat growers and agronomists learn to live with.

Mr Connabeer say effort is much better focussed on improving crop rooting and vigour through nutrition and disease control to boost growth quickly past the susceptible stage and mitigate any impact from the virus on final yield.

Furthermore, issues with insecticide resistance in grain aphids (the main BYDV vector in eastern and northern areas) mean growers must be cautious if planning to use a pyrethroid, as spraying may be ineffective and could exacerbate the build-up of resistant populations.

Longer-term, the use of integrated pest management is vital to manage BYDV risk. This includes:

• Earlier drilling
• Removing green bridges
• Selecting more resistant varieties (see below).

Growers are urged to monitor aphid risk by following the AHDB/ Rothamsted alerts (https://cereals.ahdb.org.uk/monitoring/aphid-news.aspx)

Exploring varietal differences

Research at the Hutchinsons RTC near Carlisle is investigating whether crop colour at emergence has any impact on BYDV susceptibility, as aphids are naturally attracted to more yellow plants.

The work follows on from trials at two other sites last year that suggested there could be significant differences in varietal susceptibility to BYDV.

Visual infection of 23 barley varieties at sites in Cornwall and another further north was assessed through the season and each one given a resistance score, similar to the BYDV rating previously included on the Recommended List.

This revealed a wide disparity between the best and worst varieties, with the lowest performer scoring four (equivalent to 60% infection) and the highest ranked nine (5% infection).

“It’s only one year’s results from two sites, but I’m confident there will be varieties that are naturally resistant to BYDV by parentage, so we’re looking into this again this year,” says Mr Connabeer.

This year’s research at Carlisle aims to better understand whether the differences are due to true varietal resistance, or a physical effect of crop colour, explains Miss Brown.

Ten spring barley varieties are being assessed. Aphid traps within the plots are checked twice a week and physical characteristics, such as crop colour, stress, vigour at emergence, are also being recorded.

“We want to identify whether there are any differences in the arrival of aphids into crops with different physical characteristics as well as see if last year’s varietal differences in tolerance/resistance are repeated.

“Interestingly, we’ve just seen the first aphids arrive and they were in the most yellow variety.

“Improving our knowledge of varietal differences will be vital if aphids and BYDV are more of an issue in this region in the future and chemical control options become even more limited,” she adds.

Find out more about the research at the Carlisle RTC open day on 19 June. Go to http://www.hlhltd.co.uk or email bookings@hlhltd.co.uk