It is early days to predict whether cereal crops will be susceptible to barley yellow dwarf virus (BYDV) this year, not least because drilling has been delayed due to adverse weather conditions, shortening the period during which the crop is susceptible to aphid attack.
In the last week, however, temperatures have been higher, which appears to have led to higher counts of bird cherry oat aphid, a potential carrier of BYDV (see panel).
Nick Wall, independent agronomist at Crop Management Partners, who covers Hampshire, Dorset, Wiltshire, Oxfordshire and Berkshire says seed which was treated with a dressing, for example, Deter (clothianidin), will have 4-5 weeks’ cover.
“Monitoring of crops for bird cherry oat aphid should begin from then on or just before. The signs are there may well be some aphids around. The inclement weather forecast for the end of the week will tend to slow aphid migration into the crop.”
While the start of drilling was delayed in Mr Wall’s area, much progress has been made in the last two weeks and it is now about 90 per cent complete, he says.
Kent-based Agrii agronomist Neil Harper says he uses an Agrii BYDV app which takes account of drilling date and cumulative temperature from local weather stations to determine when crops are in need of spraying. “For the guys who drilled in mid-September, so far it has been low pressure but warmer temperatures could bring it on quicker. Most people have not gone before September 20, waiting for the conditions to be right.”
But some growers have seen high levels of damage due to BYDV over the last few years, says Mr Harper. “We need to learn to manage it if Deter disappears.”
While more selective insecticides have a place, more use of technology to make more precise recommendations on their use will also be important in future, and cultural controls may also have a role, he says.
“I’m not sure if companion cropping may have a place in wheat. I am nervous where we are going away from a clean break for soils. With cover crops and cross compliance there is biomass all year round which keeps the aphids going and makes spaces for them.”
Data from the Rothamsted/SASA suction trap network, which includes 16 sites across the UK, show that numbers of bird cherry oat aphids - which can carry BYDV - at some suction trap sites remain at more than 1,000 individuals and are higher than the sites’ 10-year mean.
Testing at Rothamsted in the week October 2-8 has shown that four per cent of these aphids are of the cereal colonising form. And of 100 bird cherry oat aphid individuals tested this year for BYDV 10 per cent were carrying the virus.
However, caution is advised when interpreting these data as aphids that have located unprotected crops will continue to do well at temperatures higher than 3degC, according to the latest edition of AHDB Aphid News.
Sites recording higher numbers of bird cherry oat aphid than the 10-year mean include Broom’s Barn (Bury St Edmunds), Hereford, Writtle (Essex), Silwood Park (Ascot), and Wye (Kent).
Source: AHDB Aphid News