Mild autumn conditions heighten BYDV threat - Duncan Connabeer - Anglia Farmer

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  • Early infection can lead to bigger losses
  • Management means careful monitoring
  • Last chance for neonicotinoid dressing

Mild weather and early emergence of winter cereals may mean aphid populations establish quickly this autumn – posing a threat of barley yellow dwarf virus (BYDV) infection.

BYDV is the most widely distributed viral disease of all cereals.  It generally affects barley and oats to a greater extent than wheat, with early infections holding the potential for significant yield losses.

The yield impact is generally greatest when plants are infected while small, explains Hutchinsons technical support manager Duncan Conabeer.  Winter cereals are generally considered as susceptible up to growth stage 30, he adds.

Damage can be accentuated by the speed at which the virus is transmitted between insect and crop.  Aphids can become infected within 24 hours of feeding and re-infect healthy plants in less than a day, says Mr Conabeer.

This autumn is the last opportunity for UK growers to use neonicotinoid seed dressings containing the active clothianidin (Deter/Redigo Deter).  The final date of issue is 19 December 2018 after which growers will only have pyrethroids to fall back on until new insecticides arrive.

The years 2012 and 2016 were relatively high pressure and notably difficult season for BYDV control says Mr Conabeer.  But 50% of the wheat crop still had a neonicotinoid seed dressing.

“Looking ahead, we are moving into an even more challenging situation as many growers and agronomists will not have experience of managing BYDV without dressed seed, especially in high risk scenarios.”

Without clothianidin, BYDV management will require careful monitoring, cultural and chemical control methods.  It is important to get control correct from the start because crops will be at risk if there is suddenly a significant flight of aphids.

“There is no second chance with BYDV,” says Mr Conabeer.  Growers should identify potential risk periods to control populations of vector aphids and reduce virus inoculum, but it is unlikely that growers will be able to maintain BYDV levels as low as in the past.

“Whilst the latest monitoring by AHDB and Rothamsted suggests aphid activity remains low, with the current mild autumn conditions the threat is high as aphid flights will continue much later than usual – the risk only goes away once aphids stop flying – its not controlled by diary date.” 

Grain aphids, bird cherry oat aphids and rose grain aphids can all transmit BYDV so there’s a need to control all of these particularly in mild autumn conditions where aphids keep flying.

Issues have been observed from low levels flying into crops late then multiplying in mild autumns and winters leading to significant secondary infection.

Mr Conabeer recommends that crops sown in high risk areas including East Anglia – should use Deter or Redigo Deter for early drilled crops.

“This will provide about 6-8 weeks protection when the crop is at its most vulnerable during emergence and establishment.  The added benefit of dressed seed is that it is a useful management tool where subsequent treatments may be delayed by the weather.”

Hutchinsons agronomist Conor Campbell says growers should consider using an aphicide spray where seed has not been protected.  The message is not to delay treatment when warnings are issued, he says.

“Whilst trials suggest the optimum timing for single sprays is between mid-October and early November, depending on emergence dates, any crops that were through the ground in late September or early October may benefit from an earlier spray.

“Pyrethroids do still have significant impact on aphid control.  We only have resistance recorded in the grain aphid, so it is important to use cultural methods to reduce the risk of BYDV initially.”

A focus on improving crop rooting and vigour through nutrition and disease control can boost growth quickly past the most susceptible stage since aphid’s area attracted to yellow crops and this is also true of crops affected by herbicides.