Barley yellow dwarf virus (BYDV) management in cereals

Barley yellow dwarf virus (BYDV) is a yield-robbing disease of UK cereals. Learn about the main aphids that spread it and how to manage their levels in crops.

BYDV is the most economically important virus in UK cereals: wheat, barley, oats, rye and triticale.

Although it can affect around 80% of the total cereal area, the actual area impacted tends to be much lower.

The scale of yield loss depends on aphid activity, BYDV presence and strain, growth stage at infection and environmental conditions.

Very early infections can result in plant death. 

In the case of severe infections, BYDV can cause losses of up to 60% in winter wheat and 50% in winter barley. However, such losses are rare.

Following the withdrawal of neonicotinoid seed treatments in 2018, the routine use of foliar pyrethroid sprays increased to target aphid vectors.

Although pyrethroids are relatively cheap, every spray puts pressure on non-target organisms and increases insecticide-resistance risks.

Moderate levels of pyrethroid resistance are already widespread in UK grain aphid populations, so it is essential to follow resistance management guidance and target chemical control carefully.

This includes using integrated pest management (IPM) to reduce the need for and to carefully time sprays.

As aphids do not pass the virus on to their offspring, they must acquire BYDV through feeding on infected host plants.

The time between acquisition and the aphid being able to transmit the infection is 12 to 48 hours.

In addition to feeding on the foliage, aphids can also feed on crop roots, especially in warm, moist conditions.

Initially, only a small proportion of aphids is likely to carry BYDV. However, because of the way in which virus spreads from plants to aphids, even initial small populations of infected aphids can lead to significant economic damage.

BYDV is introduced into cereal crops in two ways:

1. Indirect transfer by winged aphids, from grass or volunteer cereals, which is the most common source of BYDV infection.
2. Direct transfer by wingless aphids, from grass or on volunteer cereals, which is called the ‘green bridge’ effect.

In most years, aphid flights stop when temperatures drop below about 11ºC.

Aphid activity greatly reduces when temperatures drop below 3ºC.

Manage aphid colonisation and spread, especially before growth stage 31.

• Select lower-risk fields, such as those with a low amount of surrounding grassland
• Encourage natural enemies, such as predatory beetles and web-spinning spiders. Although these help control aphids, it may not prevent virus transmission
• Manage ‘green bridges’ that transfer aphids/virus to new crops. For example, wait five weeks before cultivating and sowing, and destroy any weeds, especially annual meadow grass and volunteer cereals
• If glyphosate is used, destroy weeds in sufficient time to avoid dying weeds coinciding with the emerging crop, as this can cause aphids to rapidly colonise young crops
• Note that aphid colonisation is generally lower on fields with minimum tillage and retained straw may also benefit natural enemies
• Grow varieties with resistance or tolerance to BYDV, where appropriate
• Drill crops as late as possible, as crop emergence date is possibly the most important BYDV-risk factor
• Assess aphid activity to target sprays
• Use monitoring tools and services
• Minimise general stress to plants

Notes

Milder conditions are more common in fields close to the sea, which can increase aphid/BYDV risks, as can anything that promotes a relatively warm microclimate.

Aphid numbers can also be higher in fields next to woodland and treelines.

The greatest yield impacts tend to be associated with early infection, with infection impact gradually decreasing at later stages, with negligible yield impacts after growth stage 32.

Decision support tools can indicate high-risk periods and guide management interventions.

The use of specialist categories and described types allows the specific recommendation of varieties with novel traits in the AHDB Recommended Lists for cereals and oilseeds (RL).

BYDV resistance/tolerance in cereals is a specialist trait recently added to the RL:

• RL 2021/22:RGT Wolverine was the first winter wheat variety added with resistance to BYDV
• RL 2022/23: KWS Feeris was tge first winter barley variety added with tolerance to BYDV

Several varieties are now cited as having this specialist trait.

A resistant variety typically shows no or few symptoms, because it prevents virus replication, and has no significant yield loss.

A tolerant variety may show substantial symptoms, but it will not suffer significant yield loss as a result.

Although various species of cereal aphid transmit BYDV, two species are particularly important in the UK.

Bird cherry-oat aphid is the most significant virus vector, partly due to the relatively high numbers that fly during autumn.

Grain aphids tend to be most problematic in crops that are sown very early or where there is poor green-bridge management.

Although BYDV can also be spread by rose-grain aphids, this species is generally unimportant as a vector, as it is not normally found in cereals in the autumn, as it overwinters on roses.

BYDV is a complex of viruses made up of variants/isolates, with some transmitted by more than one aphid species. For example:

The genus Luteovirus:

• BYDV-PAV is spread by several aphids, including bird cherry-oat aphids and grain aphids
• BYDV-MAV is spread by grain aphids

The genus Polerovirus:

• CYDV-RPV, formerly BYDV-RPV, is mainly spread by bird cherry-oat aphids

Notes: A genus contains closely related species. The two genera cited are distinct and related, but not as closely related as the viruses within each genus.

CYDV = Cereal yellow dwarf virus.

Leaf yellowing

Infections cause leaf yellowing and stunting. Initially, symptoms are confined to individual plants scattered throughout the crop. Eventually, distinct circular patches develop. Sometimes, these patches can merge to form extensive areas of infected crop.

Red tipping

Red tipping of upper leaves can also occur. 

The Rothamsted Insect Survey provides information on regional aphid activity from the suction-trap network.

AHDB also publishes a regular snapshot of the proportion of virus-carrying bird cherry-oat aphids and grain aphids in the autumn.

The results are based on BYDV/CYDV tests of a small number of aphid samples collected from four suction traps, located across England.

Use this monitoring information to support in-field observations.