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Keeping ahead of BYDV

With aphid numbers at high levels as warm weather continues, cereal growers are being advised to assess the BYDV risk in early sown crops.

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Bird cherry-oat aphid numbers are more than the 10-year mean and accumulated numbers are exceeding the 10-year average for most monitoring sites, apart from in Northern Britain, according to AHDB’s Aphid News.

 

However, although bird cherry-oat aphids can carry barley yellow dwarf virus (BYDV), authors of the bulletin advise caution when interpreting these data as the number of cereal colonising aphids found from testing at Rothamsted in the week of October 8-14 was far lower than for the equivalent week last year.

 

The Aphid News bulletin says: “Only a small proportion of aphids entering cereals are likely to be carrying BYDV. Problems with spread arise when the second generation offspring of the original winged colonisers are produced.

 

“This is usually the generation that begins moving significantly away from the plant originally colonised.”

 

The timing of the second generation can be approximated by accumulating daily average air temperatures above a baseline temperature of 3degC. It takes about 170 ‘day degrees’ (DD) for the second generation to be produced, says AHDB.

 

It has recently launched a new BYDV management tool which helps to indicate when this threshold has been reached and can be accessed at cereals.ahdb.org.uk/bydv


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BYDV management tool

 

The BYDV management tool features a UK map of weather stations. Users can select their nearest weather station and a start date using the slider for DD calculations (see panel). Once 170DD has been accumulated, the relevant line on the chart displayed enters the yellow zone. At this stage, crops are estimated to be at an unacceptable risk and treatment should be considered, explains AHDB.

 

Frontier agronomist, Andrew Roy, based in Northern England, says: “With early drilling and mild weather, we’ve had to watch out for barley yellow dwarf virus (BYDV) aphids and spray accordingly.

 

“Thankfully, much of the early sown crop was Deter-dressed which should safeguard against early infection. With the withdrawal of Deter, we will need to consider delaying our drilling date next autumn to help manage the BYDV risk. By that time, it is also hoped that a long-awaited foliar insecticide will finally make it onto the market.”

 

There have been reports of a major aphid flight along the south coast, meaning that cereal crops are at high risk of BYDV, according to Hutchinsons agronomist Elle Pace, based in Sussex.

 

“Where seed has not been protected, use an aphicide spray and don’t delay treatment when warnings are issued.

 

“The minute the crop pokes through the ground it is at risk, and as the current threat is so high the advice would be to spray an aphicide onto the crop around the one leaf stage, don’t wait for two leaves – this should provide about seven days’ repellent activity – that is providing the aphids show no sign of resistance.”

 

When should day degree (DD) calculations begin?

  • On the day of emergence for untreated crops.

 

  • When aphids are present and protection from neonicotinoid-treated (clothianidin) seed has run out which is around eight weeks after sowing (clothianidin is only available for cereals drilled before December 19, 2018 when it is subject to an EU ban).

 

  • Following a pyrethroid application - account for product persistence, (see label).

Source: AHDB

 

New BYDV research

A new project funded by AHDB and led by the Game and Wildlife Conservation Trust to help develop a BYDV monitoring system began earlier this month.

 

The project aims to:

  • Assess the feasibility of developing a field-specific decision-support system for BYDV.
  • Evaluate the use of field-specific monitoring methodology for aphid vectors of BYDV and the use of a degree day tool to predict spray timings and BYDV infection levels.
  • Test whether landscape composition, aspect and type of tillage affect immigration of aphids.
  • Provide key messages on BYDV management.
  • Provide recommendations on further research needed to develop field-specific monitoring and a decision-support system.
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