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Don’t ignore the threat from BYDV – Nick Wall

Don’t ignore the threat from BYDV – Nick Wall, October 2017

Cereal growers are warned not to be complacent in protecting their crops against Barley Yellow Dwarf Virus (BYDV) as temperatures remain warm heading into autumn.

Barley Yellow Dwarf Virus (BYDV) is spread by bird cherry-oat and grain aphids and can affect all cereal crops, but particularly barley and oats. Symptoms are leaf yellowing and reddening associated with stunted growth and severe infections can result in significant yield losses.

Peak autumn flights of Rhopalosiphum padi (Bird cherry-oat aphid), the main BYDV vector in England increase in favourable weather during September and typically don’t decline markedly until after the first week of November.

“Recent winters, such as in 2015 and 2016, saw some very high levels of BYDV infection in untreated crops in regions where the mild autumn temperatures resulted in aphids flying until Christmas,” says Dr Bill Lankford, country manager for Life Scientific.

“Autumn infection can lead to yield losses of as much as 2.5t/ha in untreated crops, so it is essential that growers fully grasp the risk and are aware of the best approach to preventing infection.”

“Growers in the traditionally BYDV high risk areas in the south and south west as well as the Deben Valley in East Anglia and coastal fringes will be well aware of the threat, but any early drilled cereals are generally at risk,” he adds.

Entomologist, Alex Greenslade, who is heading up Rothamsted Research’s Insect Survey records that the last week in September saw a rise in the total number of aphids.

The report suggests that the increase in aphid numbers despite the fall in average air temperature in late September,  is a sign that this year’s autumn aphid migration is underway and particularly so for the bird cherry–oat aphid in the north of Britain.

The report also highlights that aphids on unprotected crops will continue to do well at temperatures above 3°C.

Nick Wall independent agronomist with Crop Management Partners, who walks crops in Hants, Dorset and Wilts, takes a very cautious approach when dealing with BYDV – based on the significant impact the disease has had on crops in his area in the past.

“It’s really important to recognise that any crops that are already in the ground or will be drilled before November are at risk if it’s a mild autumn, which it has been so far. For this to change and for aphids to die off we would need about 5 days of temperatures of -5°C.”

Mr Wall points out that a seed treatment containing clothianidin (Deter) or imidacloprid (Tripod Plus) will provide protection for 4 -6 weeks, but if aphids are still invading after this, an additional foliar spray may be necessary.

Dr Lankford recommends the use of Life Scientific’s capsule suspension formulation of lambda-cyhalothrin, Lambdastar, for controlling aphids both in early and later drilled crops of wheat, winter barley and oats.

“It’s a very cost-effective product for BYDV control, used at an application rate of 50 ml/ha Lambdastar in 200l/ha water.  Typically a single spray during late October to cereals at risk of BYDV, either those that have been recently drilled and not protected by a neo-nicotinoid seed treatment, or early drilled crops where period of protection from the seed treatment has finished.”

“Although aphid migrations decline markedly in November, in mild winters treatment may be required on late drilled crops, for example in very high-risk areas when a “green bridge” is harbouring aphids prior to drilling.”

“If wingless aphids are found in previously treated crops over winter when temperatures are not low enough to cause significant mortality, a winter timed treatment could be necessary to prevent virus spread in the crop,” he adds.

For up to date information on aphid activity sign up to the AHDB aphids news service which is designed to assist decision-making relating to spraying.