Get the sprayer out for fungicides…not BYDV

There are plenty of yellow leaves showing up in spring barley crops across the country; particularly in the last week.

The issue raises the concern over control of barley yellow dwarf virus (BYDV) in the season ahead as neonicotinoids are now banned and aphids continue to show signs of resistance to pyrethroid sprays.

Some crops may also be stressed from cold weather and there is a possibility of trace element deficiencies in some fields, but the main cause of these yellow leaves is most likely BYDV.

Similar to two years ago, the infected plants are mostly showing up in single leaves scattered throughout the crop, unlike many winter barley crops this season which showed clear yellow patches of infection.

Nutrition

As mentioned above, some discolouration on the plant may be due to nutrient deficiencies, but growers will know the difference in the field. If a plant is deficient in nutrients – major or minor – it will not perform to the best of its ability.

Fighting disease and virus becomes more difficult in a plant in this case. Where nutrient deficiency is the problem this season, plan ahead for next year and take note of deficiencies in different fields. It might be an idea to consider adding leaf analysis early in the season to your plan.

Teagasc’s view on BYDV

AgriLand spoke to Shay Phelan – Teagasc tillage specialist – about the problem and he said there is nothing farmers can do at this stage. He added that it looks like a late infection of BYDV, as it is showing in crops which were both treated and not treated with an aphicide.

The impact on yield is unclear and will remain so, while it might be very little there is no definite way of knowing.

Late sown crops, as always, were more at risk and are showing symptoms of the virus.

T2

One thing that should be done is applying T2s on spring barley. Farmers should be aiming to apply their T2 fungicide to crops when the awns are peeping.

Recent rain will add to disease pressure and an SDHI/triazole mix should be applied with chlorothalonil at 1L/ha.

Adapt the rate of the SDHI and triazole according to disease pressure. At least a half rate should be applied and with disease pressure increasing – and as part of a good integrated pest management strategy – robust rates should be applied. Farmers should be aiming to move towards the higher end of the label rate to ensure good protection into the remainder of the season.

The important thing to remember is not to run to the field with an aphicide in the sprayer. The damage has been done on that front.

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