Tips on controlling BYDV in a high-pressure autumn
© Mark Sanderson Higher numbers of aphids combined with an earlier start to drilling and glyphosate shortages mean that the barley yellow dwarf virus risk could be higher this autumn.
The virus, which is spread by the grain aphid and bird cherry-oat aphid, can lead to costly losses in winter barley and wheat, especially with early infections.
See also: Crop Watch: BYDV warning as cereal drilling starts early
BYDV facts
- Barley yellow dwarf virus (BYDV) is a persistent virus that will be carried by an infected aphid all its life
- The main vectors for BYDV are the bird cherry-oat and grain aphids
- Once aphids have the virus they will be able to transmit it for the remainder of their lives
- Plant infection will occur after about 30 minutes of aphid feeding
- Only one infected aphid needs to feed to infect a plant
- The earlier the infection the worse the impact on yield
- Warm autumns will boost aphid population build-up
What is the risk?
Syngenta field technical specialist Max Newbert points to the long-term forecast this autumn of temperatures 0.2C higher than the norm, and average rainfall. Last year, excess rainfall resulted in lower aphid numbers.
Numbers of aphids being trapped this season are also high, about two to three times the eight-year average. “So the pressure is there,” says Dr Newbert.
Primary and secondary infection – what’s the difference?
- Primary infection occurs when winged aphids land on single plants and transfer virus.
- Secondary infection is when the population of wingless aphids build up sufficiently to initiate aphid spread from the original infection point, causing larger area of infection. Controlling larger areas of infection from secondary or even tertiary spread is key to reducing the impact of barley yellow dwarf virus in cereal crops.
Added to this is the early start to drilling and the shortage of glyphosate, leaving some farmers unable to take out volunteers, which act as a green bridge.
“Last year we saw more infection than anticipated in a low-pressure year.”
He explains that it was due to spring crop volunteers acting as a green bridge in some areas, as there was a glut of spring cropping after the wet winter in 2019.
So it’s all pointing to a potentially high-pressure year, he says.
© Mark Sanderson
What action can be taken?
Many farmers will be taking an integrated approach and a key part of this is the targeted use of Hallmark Zeon (lambda-cyhalothrin).
Dr Newbert believes a good starting point is to keep checking the Rothamsted Aphid Bulletin, as suction trap results will give an early national indication. But they tend to be a week old by the time they are published.
For more up to date figures, farmers can access water trap data from 11 Syngenta sites across the country using the company’s BYDV Assist tool.
Five-point plan for managing BYDV carrying aphids
- Reduce the green bridge Consider how you are going to manage it if you have no glyphosate this year, and remember it can take two weeks for the majority of aphids to leave sprayed-off areas.
- Drill timing If farmers delay drilling until mid-October onwards, they will see the risk go down.
- Primary infection Try to maximise establishment to achieve the greatest plant density by using a seed treatment or increasing seed rates. Thicker crops can fill in the gaps from infection of single plants, compensating better for yield loss from primary infection.
- Resistant varieties They fit in the early drilling slot and add an extra layer of protection for high-pressure years. They can also be targeted for high-pressure fields. For example, a field with a prevailing wind from a woodland.
- Use the BYDV Assist tool to target insecticide applications When using Hallmark Zeon, apply at the full rate (50ml/ha) and aim for optimal application conditions, such as dry leaves.
The tool aims to help farmers optimise their insecticide spray timing to target the second generation of aphids, based on a model using the T-sum 170-day degrees (DD) threshold.
“The idea is to use as little [insecticide] as possible and get the biggest effect of control.”
Farmers just simply put in details such as location and crop emergence date.
The tool will give users a 145DD warning to go and check if aphids are present. This gives two to three days to check crops before the 170-day timing for spraying, he explains.
Yellow sticky or water traps can then be deployed in fields. If aphids are found, then it’s time to spray. If no aphids are present, then there is no need to spray.
The tool also shows forecasts for the T-sum, using the fields’ 30-year average weather data to give an early idea of when risk could start.
Once sprayed, the tool will reset the T-sum calculation for one week, after which it will then start to forecast the next generation. Spraying is generally every two weeks in September and every three to four weeks in October as it cools.
How an ‘aphid-rearing nursery’ can help
Syngenta has established its own aphid-rearing nursery so that it can carry out trials examining the spread of barley yellow dwarf virus.
This will give the company the ability to do trials in the UK to test potential new treatments without the risk of ending up with no data in a low-risk year.
© Mark Sanderson
It will be especially important for testing new treatments that target viruses rather than the aphid, says the company’s Max Newbert.
“Elicitors, which trigger the plant’s own defences, look really interesting, but there is a need for a better understanding of how to use them.
“For example, what is the best way to use them? A seed treatment or foliar spray?”
He is also planning to look at varietal resistance. “The virus can still infect the plant, so it’s more akin to how our industry understands tolerance .”
BYDV Assist – how it works
- Add your field by pressing the + icon in the bottom right corner.
- Input your location, BYDV Assist uses a 4km-accurate weather model.
- Select your drilling and emergence date, this is when the 170-day degrees (DD) is calculated from.
- If a foliar insecticide treatment has been applied input the date treated. This will reset the calculation to 0DD for 1 week.
- A notification is given at 145DD to allow a couple of days to inspect the field and another when the 170DD threshold is reached.
- If aphids are present when the 170DD is imminent or occurring, an application spray is recommended.
- The included spray application guide can be used to plan optimum application timings, once treatment is warranted.
