In previous years, cold weather has contributed to BYDV control through killing off some of the bird cherry oat aphids overwintering in cereal crops. However, with the mild winters experienced in the last two years, growers may need to readdress their BYDV control strategy, warns Nigel Adam, Development Manager at Bayer.
Mr Adam comments that it is generally accepted that bird cherry oat aphids can survive to -7 °C. Once the aphids stop flying, usually in early December, they burrow deep into the leaf sheathes which act like a blanket, he says.
“Despite the sharp frosts in January, overall last winter was pretty mild, as too was winter 2015. There would have been many regions in the UK that did not experience low enough temperatures last winter to affect bird cherry oat aphid populations, and certainly not within the leaf sheath where the aphids would be found.”
Mr Adam recalls a scenario in Suffolk last winter, where a grower had been disappointed to see BYDV appearing in his wheat crop despite applying Deter (clothianidin).
“The grower had drilled in early October and used Deter treated seed which would have given about 10 weeks protection from aphid feeding. However, due to the relatively cool weather and low aphid pressure, the grower had not followed up with a pyrethroid spray in early to mid-December, which would have killed any aphids subsequently entering the crop.”
Mr Adam continued “Unfortunately, whilst the weather was cold, it was not cold enough to kill off the aphid population, hence they were able to infect the crop with BYDV.”
With this in mind, here are 5 tips to help growers control BYDV in mild conditions:
1. Monitor temperature – keep a record of the temperature throughout winter and remember that although aphids can’t survive below -7 °C, it will be warmer within the leaf sheathes.
2. Follow up treatments – when aphid activity is unusually late, or in areas of particularly high risk where aphid activity is heavy and prolonged and mild weather predominates, crops treated with Deter may require a follow up pyrethroid treatment. Early September drillings may need a follow up spray 6-8 weeks after drilling; Mid- late September drillings after 8-10 weeks and early October drillings after 10 weeks.
3. Monitor aphid numbers – utilise data from the AHDB’s alerts to understand the number of aphids flying. Last winter there were still aphids flying in mid-December across the country, which highlights how mild conditions can affect activity.
4. Be vigilant – it only needs to be a few degrees above zero for bird cherry oat aphids to emerge from leaf sheathes and begin to spread the virus even if they have ceased to fly, so keep an eye on temperatures as spring approaches and use a follow up pyrethroid spray when appropriate.
5. Don’t forget – BYDV is an ‘invisible’ disease from infection until several months after. In winter barley symptoms usually express by April following drilling and in May for winter wheat. The earlier the infection, the greater the impact on yield so if in doubt, get protection from the moment of drilling.
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