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Barley Yellow Dwarf Virus (BYDV)

BYDV is spread mainly by aphids and is one of the most destructive virus diseases in the world. Small grain cereals and many wild and cultivated grasses are susceptible. The virus reduces root growth, causes loss of colour in the leaf margins followed by the yellowing and relative dwarfism of the plants starting with the boot stage.

BYDV can be introduced to all autumn sown cereals by aphids and causes stunted yellow plants which are not seen normally until the spring. Yield losses, as many found out in 1999, can be high.

Crops following grass or weedy stubbles and all crops brairded before mid-October are at greatest risk. BYDV normally first appears early in the season usually along field margins. It later develops in roughly circular spots which can reach more than 30 feet in diameter. As the season progresses infected patches grow

Description

Leaf discolouration appears as shades of yellow, red or purple from tip to base and from margin to midrib. Look for yellowed or reddened leaves. Infected plants may be stunted and scattered among healthy plants. The first symptom detectable in the barley field is the yellowing of the leaf tip, more particularly the last leaf under the head. In oats contamination is signaled by the reddening of the leaves.

Note that these symptoms are sometimes confused with nutritional disorders, physiology factors or bacterial toxins. Yellowing can be confused with nitrogen deficiency and BYDV symptoms are not easy to distinguish from those caused by aster yellow.

Infection

The virus is transmitted by aphids during the Autumn. Aphids feed on contaminated plants and so become carriers of the disease. They can then infect healthy plants for the rest of the lives after a short latent (up to 48hrs) period. They do not, however, transmit the infection to their next generation.

Contaminated weeds and wild grasses can also be a cause of inoculum.

The dissemination of the virus mainly depends on the movement of aphid populations. Cool (10 -18 degrees C.) and humid seasons favour the reproduction and the migration of the virus.

Infections can occur throughout the season and are most abundant when there are high populations of aphids present. The leaf discolouration symptoms that indicate viral infection develop within about 2 weeks of inoculation at temperatures between 18-21 degrees C. When infections occur at temperatures above 30 degrees C the symptoms do not develop.

Control

Full control within the field is not yet possible.

  • Good housekeeping is essential especially the removal of volunteers and other sources of inoculum. Control volunteer wheat, barley and oats because they may serve as late season hosts to the aphids.
  • Use tolerant varieties.
  • Burn-off grass swards and weedy stubbles with a desiccant at least one week before ploughing or leave an interval of at least three weeks between the ploughing of grass swards or weedy stubbles and sowing.
  • Seed treatments that incorporate an aphicide component (e.g. imidacloprid) are sometimes available and take the worry out of getting foliar aphicide timings right. These treatments should be particularly useful for fields with a history of BYDV problems or on heavy ground that makes autumn spraying difficult.
  • Crops deemed to be at high risk, which did not receive a seed treatments or where aphids are present, should be treated soon after the two leaf stage with an approved aphicide. A follow-up treatment may be necessary.
  • Planting date affects the severity of the disease and yield loss. Early planted winter cereals and late planted spring cereals may be subject to high aphid populations at early growth stages, resulting in greater yield loss. Low seed rates also increase the pressure. Fewer plants mean more aphids per plant.
  • Oat varieties differ in their susceptibility to this disease but there is no effective resistance in any of the cereal crops.
  • Control based on aphid monitoring can be useful. Basing spray decisions on accurate risk forecasts could save money, preserve non-target beneficial insects whilst minimising threats of insecticide resistance developing. Risk forecasting is based on mathematical models. Aphids are trapped and counted UK-wide in autumn to assess numbers migrating to crops. Using this information and weather data pedictions of risk become possible.
  • Continue monitoring risk throughout the winter. Apply mid-winter or late-winter sprays at the appropriate time if necessary to any crops predicted to be at economic risk of late infection.

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