Advances in crop genetics, more accurate monitoring of aphid populations and appropriate cultural controls are key weapons in beating the growing threat of viral diseases such as BYDV in UK barley crops.
Growers drilling barley crops in the next few weeks need to be mindful of the threat of barley yellow dwarf virus (BYDV) and take appropriate management steps to avoid its worst effects, industry commentators are advising.
With a reduced selection of insecticides available to control aphid vectors, integrated crop management is seen by many as the way forward with developments in varietal tolerance playing an increasingly important role.
Extending the time between cultivation and drilling, using herbicides to destroy any ‘green bridge’ and sowing varieties able to thrive even when infected all have a role to play in mitigating against the problem.
According to ADAS entomological research consultant Sam Telling, whilst latest results from the Rothamsted Insect Survey point to a lower initial migration than in 2021 and below the ten-year mean, this is a poor indicator of BYDV likelihood by itself.
“The autumn migration of the two main vectors of BYDV, bird cherry-oat aphid and grain aphid is currently ongoing, with the start occurring in early August and the peak typically occurring in the first two weeks of October.
“Migrations are seldom large enough to cause significant virus spread within crops with the primary cause for in-crop BYDV infections being the short distance migration of the second generation offspring of the original colonisers.
“This occurs after an accumulated 170 degree days after crop emergence above the 3oC minimum for bird cherry-oat aphid and grain aphid development and is a sign that BYDV spread within the crop is likely.”
Be aware of the risks
Furthermore aphid numbers don’t directly translate to prevalence of BYDV, he points out.
“In an AHDB funded project led by ADAS, half the number of aphids were caught in traps in 2020 compared to 2021, whereas the percentage of BYDV positive aphids decreased by 5-10% between 2020 and 2021.
“Rothamsted Research also release updates for the percentage of aphids that are carrying BYDV. In the first two weeks of August, the most recent data available, the average percentage of aphids carrying the virus across four suction traps was 20% for bird cherry oat aphid and 38% for grain aphid."
Growers need to be aware of the greater risks to crops in order to help with future management of BYDV, he advises.
“The risk is greatest in the west and south-west of England, south-west Wales and in the north-east, where there is a greater proportion of permanent grassland that can act as a sink for the virus.
“Green bridge transmission, where aphids move into wild grasses from cereals in summer, accumulate, and then move into newly emerging cereals in the autumn can occur in some fields.
“Expanding the time between cultivation and drilling can reduce green bridge transmission by burying volunteers on which the aphids feeding will die before being able to move onto the new crop.
“A dessicant herbicide can also be applied if the interval between cultivation and drilling is less than 4 weeks.”
Importance of BYDV tolerance
Sarah Hawthorne of plant breeders DSV believes crop genetics will also have an increasingly important role to play in managing the affects of the virus.
“Growers are becoming increasingly aware of the problem with many in the most susceptible areas looking seriously at BYDV tolerant varieties.
“The situation has been made worse in recent years by the reduced number of suitable insecticides available and confirmation that the aphid vectors involved in BYDV transmission are becoming resistant to the pyrethroid chemistry commonly used.
“The conventional cultural control of delaying drilling until the cold weather starts to kill the aphid population can work well, but barley growers need to be mindful of significant yield drops the later the crop is sown.”
Which leaves varietal tolerance as the most reliable starting point for dealing with the problem long-term, she believes
“Varietal tolerance means plants may get infected but if they do, they will remain unaffected by the virus’ presence and continue to grow normally.
“It’s not a new concept but it is one that has become increasingly relevant following the ban on neonicotinoid seed treatments which until recently made it largely unnecessary.
“The YD2 protection gene carried by our own BYDV tolerant variety DSV Sensation, for example, is well established but its potential has only recently been fully appreciated.”
Whilst BYDV is the main focus of attention regarding viral diseases in UK barley, European experience suggests others such as barley yellow mosaic virus (BYMV) are a growing problem, she says.
“Type 1 BYMV protection is now standard across many varieties but Type 2 BYMV is now common in many areas of Europe.
“Results from DSV in Germany show that the yield effect between BYMV 1 and 2 resistant varieties and only BYMV 1 resistant varieties can be between 10% to 40% in fields with BYMV strain 2.
“DSV Sensation combines BYDV tolerance with resistance to barley yellow mosaic virus (BYMV) strains 1 and 2 so that gives another layer of protection should such problems become more widespread in the UK.”
High performance DSV Sensation
Such in built genetics can be valuable allies in the fight against virus diseases in barley but will always work best when used as a foundation for an integrated approach to pest management, Sarah Hawthorne says.
“Whilst DSV Sensation does give protection against BYDV and BYMV, an insecticide spray may still be necessary to ensure that the aphid population is contained.”
Growers worried that such agronomic benefits come at the cost of reduced yields, should be comforted by Sensation’s overall performance figures, she says.
“Apart from the tolerance to BYDV and resistance to BYMV1 + 2, Sensation is proving to be a strong six-row performer with a good all round disease resistance package.
“Sensation has high untreated yields allied to other important traits such as good straw stability to make it a very popular all-round proposition for barley growers.
“As well as a high specific weight, Sensation also has outstanding spring vigour making it one of a the most competitive varieties against blackgrass currently available.”
“In trials in France Sensation has achieved yields of 107.4% of control compared to other popular BYDV varieties with a specific weight of 67kg/hl.
“Sensation has also demonstrated an ability to head up to 5 days earlier than other popular BYDV varieties – 128 days compared to 133 – as well as being suitable for early sowing dates.
“Other European trials have showed similar results as well as highlighting untreated yields of 93% of treated control and exceptional resistance to lodging.”
Growers wanting to track aphid populations in their area should visit the Rothamsted Insect Survey on aphid migration https://insectsurvey.com/aphid-bulletin
Further advice and updates on BYDV prevalence and management together with other information on diseases and weeds can be obtained from ADAS’ weekly Crop Action issue.
The AHDB BYDV tool (https://ahdb.org.uk/bydv) can also be accesses to indicate when 170 degree days has been reached and when crops should be inspected for aphids.