
Growers face a tough decision when it comes to tackling barley yellow dwarf virus in autumn cereal crops.
• Virus threat expected to be high
• No-insecticide crops pay £45/ha
• Think before abandoning sprays
With high aphid pressure forecast, the virus risk is expected to be high. Yet the Sustainable Farming Incentive option IPM4 is offering farmers £45/ha not to use insecticides on arable and permanent crops.
The payment means many growers many be tempted to reconsider their use of pyrethroids, says agronomist Chris Martin of Agrovista, who has been exploring ways to minimise BYDV yield losses.
With a perfect storm scenario of early drilling, aphids already populating high levels of volunteers and mild autumn temperatures, Mr Martin believes abandoning pyrethroids would be taking a massive gamble.
Pros and cons
“After some incredibly wet recent autumns, growers understandably want to drill early to ensure they actually get a crop in. But the flip side is that delayed drilling is still one of the best ways to avoid the worst effects of BYDV.”
Glyphosate is often used to destroy the green bridge from last year’s stubble. But that could be made more difficult this year with lots of volunteers returned to many fields and wingless aphids surviving on this material post-drilling.
“Some growers will turn to winter wheat varieties with a lower susceptibility to BYDV, but they are not a silver bullet,” says Mr Martin. “In my experience, they tend to perform much better against BYDV when partnered with an insecticide.”
All things considered, Mr Martin says pyrethroids are still worthwhile in high pressure aphid situations. “Quite simply, pyrethroids still work successfully on susceptible pests and are one of the few insecticides that can still be used on cereal crops.”
Although all pyrethroids are susceptible to some level of resistance, Mr Martin says they are also all different in their chemical make-up – so the best strategy is to select different pyrethroids for different crops.
Wider impact
The pyrethroid esfenvalerate, for example, is a potentially better candidate for cereal crops with resistance issues because it isn’t used on oilseed rape. “It’s both less aggressive and poses a lower toxic risk to beneficial insects,” says Mr Martin.
The sole manufacturer of esfenvalerate is Sumitomo Chemical. Business manager Simon Leak says the company takes product safety to beneficials seriously. Esfenvalerate has lower toxicity levels to bumblebees, he says.
The main vectors for BYDV are bird cherry-oat aphid and grain aphid. Grain aphid is moderately resistant to pyrethroids but there are no current reports of resistance or control failures in bird cherry-oat aphids, says Mr Leak.
Disruptive
The impact of esfenvalerate on web-spinning spiders – the main predator of aphids – is minimal, with the active only proven to be initially disruptive to the spiders with no long-term harmful effects, he says.
Compared to other pyrethroids, esfenvalerate has the lowest amount of active ingredient at its recommended BYDV dose rate, says Mr Leak. It also has longer photo-stability, he adds – a useful property in an insecticide.
AHDB advice on minimising virus risk
Barley yellow dwarf virus is the UK’s most economically important cereal virus, says the Agriculture and Horticulture Development Board.
Severe infections can cause losses of up to 60% in winter wheat and 50% in winter barley. The AHDB says these loss levels are rare but it is continuing to monitor BYDV in cereal aphids this autumn.
To tackle the virus, the AHDB recommends selecting lower-risk fields, such as fields with a low amount of surrounding grassland. It also suggests encouraging natural enemies, such as predatory beetles and web-spinning spiders..
Green bridges between crops should be managed appropriately – for example by waiting five weeks before cultivating and sowing, and destroying any weeds – especially annual meadow grass and volunteer cereals
Aphid colonisation is generally lower on fields with minimum tillage. The AHDB says this is because retained straw may also benefit natural enemies. And it recommends drilling crops as late as possible.
Growers should also use monitoring tools to assess aphid activity, manage aphid colonisation and spread, minimise general stress to plants and select BYDV-tolerant varieties, where appropriate.
For the latest updates, visit https://insectsurvey.com/aphid-bulletin
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