Big rise in bird cherry-oat aphid numbers

Bird cherry-oat aphid numbers continue to escalate this autumn, increasing the risk of barley yellow dwarf virus transmission to early-sown winter cereals, particularly in the south and west.

Latest data from Rothamsted Research’s nationwide network of 16 suction traps shows well over twice as many bird cherry-oat aphids were caught between 12th and 19th September than the previous week (see graph).

In all, 8,194 bird cherry-oat aphids were captured, a rise of 4,788 on the week. The total surpasses last year’s peak of 7,098, which was not reached until 4th October.

Dr Cathy Hooper of RAGT Seeds says: “As well as the massive and earlier increase in bird cherry-oat numbers, we are also seeing a very interesting trend in the proportion of cereal colonisers, the asexual clones that remain on cereals and produce nymphs that spread the disease within a field.

“Due to the mild winter last year and the warm, calm weather of last week, these asexual clones now make up 51% of the catch, compared to the 10-year average of 30.1%.”

At first, individual plants are affected, followed by the appearance of distinct circular patches, which can merge into larger areas of infected crop, causing severe yield loss.

“Growers have to rely on well-timed pyrethroid sprays to prevent infection if numbers reach threshold, unless they are growing a variety with BYDV resistance,” says Cathy.

Currently, the only wheat variety with resistance available ln the UK is RGT Wolverine, which is widely available for sowing this autumn.

The inclusion of the Bdv2 gene, which originates from a wild goat grass and confers season-long control costs with no need to spray, costs just £15/ha (assuming a seed rate of 175kg/ha), less than buying a pyrethroid and applying it.

Cathy adds: “My advice remains as before: if you are not growing RGT Wolverine and you plan to drill wheat in the next fortnight or you already have crops in the ground, keep a close eye out for aphids throughout the autumn, and longer if the weather remains mild.

“Be sure to check leaves close to the base, as aphids often hide here and can easily be missed.”

* To find out more about BYDV resistance in wheats, please click here to see the RAGT fact sheet.

BYDV key facts

· Serious disease of wheat, barley and oats

· 82% of crops area at risk if not treated*

· Wheat yield losses in untreated crops average 8% but can hit 60%*.

· Control:

o Resistant varieties (wheat - RGT Wolverine)

o Well-timed pyrethroid sprays

* Source: AHDB

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