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Downy Mildew - Beet

Peronospora farinosa

Pathogen

Fungus

Hosts

Sugar beet, beetroot.

Symptoms

Heart leaves are light green, thickened, distorted and develop a purplish downy growth. Older leaves may turn yellow similar to the symptoms of virus yellows.

Development

The disease is spread by air-borne spores from infected beet seed crops, mangold seed crops, groundkeepers, old clamps, cleaner-loading sites or wild beet. Infection can also arise from resting spores (oospores) in the soil.

Favourable Factors

Cool, humid weather following crop emergence.

Importance

Infection in June can seriously affect root yield, whereas infection in July will reduce sugar content. Heavy losses due to downy mildew have been reported in seed crops grown on the continent.

Whilst it can be a serious problem in some countries, it has not been a major problem in the UK as damage is usually restricted to odd plants in fields.

Control

  • Avoid more susceptible varieties

  • Separate root and seed crops

  • Remove ground keepers, growth on old clamps and wild beet

  • Beet in set-aside should be controlled before sowing beet in neighbouring fields

  • No fungicides are available for control of downy mildew in sugar beet.