Defra

On 1st April 2002, the UK (except Northern Ireland) relinquished its protected-zone status for this disease. Rhizomania is no longer considered to be a quarantine disease and no statutory measures are applied to control its multiplication and spread. A number of EC member states and 3rd countries continue to apply statutory measures in order to prevent rhizomania becoming established within their borders.

Rhizomania is a disease of beet (Beta vulgaris subsp. vulgaris) caused by the virus, Beet necrotic yellow vein virus (BNYVV). The disease is most serious on sugar beet although it is also known to infest fodder beet, mangolds, red beet, spinach beet, seakale beet, swiss chard and spinach (Spinacea oleracea).

If left unchecked, it can cause significant reductions in yield of sugar beet crops through a reduction in root weight and accompanying reduction in sugar content. Three different pathotypes (strains) of the virus have been identified, the ‘A’, ‘B’ and ‘P’ pathotypes.

Varieties of sugar beet have been developed that are both tolerant and show some resistance to infection. During the last few years these varieties have improved to the point where they give equivalent yields to the best varieties on the current NIAB recommended list. There is however uncertainty as to the degree of tolerance/ resistance that exists in currently available varieties toward the less common ‘P’ pathotype.

Infected plant showing upright, lettuce-green foliage

Rhizomania is normally seen in fields as strips or kite-shaped patches of lighter foliage within an otherwise healthy crop. There are a number of symptoms of the disease but it is unlikely that they will all be seen in an individual crop. Plants showing one or more of these symptoms may be affected by rhizomania. However, it should be noted that many other factors within the field scale environment may produce similar symptoms.

• Whole plants may be stunted with upright foliage.
  
• Leaves may be translucent, lettuce-green in colour, and may have longer stalks and narrower blades than the healthy crop. Leaves may also appear more wavy-edged.
  
• The disease causes a proliferation of fine root hairs which give the beet a bearded appearance, this symptom gives the disease its name: rhizomania or 'root madness'. Bearding may be restricted to the very tip of the tap root, while lateral roots may sometimes develop bearding some distance from the main tap root exhibiting a symptom known as ‘rat tails’.
  
• The bearding is often hidden by attached soil which can be removed in dry conditions by gentle knocking. Mechanical lifting frequently masks bearding as root tips and laterals are lost.
  
• The tap root is often severely constricted either at the top, appearing turnip-shaped, or lower down giving a barrel shape. When sliced vertically, the vascular tissue may appear fibrous and straw-yellow to brown in colour.
  
• Small tumour-like outgrowths are occasionally found along the tap root.
  
• The necrotic yellow vein symptom after which the virus is named is rarely seen in the UK due to less than optimal conditions for symptom expression.

First identified in Italy in 1955, the disease is now widespread in most sugar beet growing countries of Europe (Austria, Belgium, Bulgaria, the Czech Republic, France, Germany, Greece, the Netherlands, Romania, Spain, Slovakia, Switzerland, the former USSR and the former Yugoslavia).

Elsewhere in the world, rhizomania is found in China, the USA and Japan.

It was first identified in the UK in 1987 in north Suffolk. At present the disease is predominantly found in the counties of Norfolk and Suffolk while being more sparsely distributed over other parts of East Anglia and further afield.

The virus is carried and transmitted by the common soil dwelling fungus Polymyxa betae. When virus infected P. betae invades the roots of beet plants, the virus is released by the fungus, multiplies and spreads within the plant causing disease symptoms.

Spread from plant to plant is by the mobile spores of P. betae which are found in the soil-water. Spread within a field often occurs through cultivation; infested soil being dragged or carried on agricultural machinery, by wind-blow, irrigation runoff and livestock. Wider spread within the farm and beyond may occur as a consequence of any mechanism by which soil is moved from one place to another.

To help prevent spread of the disease onto and within your farm, you are advised to observe the following hygiene precautions:-

• Avoid bringing soil from external sources onto your farm; if this can not be avoided, you are advised to keep such soil well away from areas which are to be used for arable production.
  
• Minimise access to your farm by visiting machinery and vehicles. Where access to your land is essential, insist that all such machinery and vehicles are cleaned free of soil, and if possible disinfected, prior to their arrival. Suitable disinfectants are Antec Farm Fluid S or Panacide M, used according to manufacturer's recommendations.
  
• Ensure all farm machinery, vehicles and livestock are as soil-free as possible when moving between blocks of land.
  
• Before leaving blocks of land in which rhizomania is known or suspected to be present, it is advisable to both clean machinery free of soil and to disinfect those parts which come into contact with soil.
  
• Waste vegetable matter should ideally be returned to the field of origin, caution should be exercised before spreading onto other arable land.
  
• Similar caution should be exercised if using waste vegetable matter as an animal feedstuff when stock are to be fed outdoors and when disposing of livestock manure and residues.

If rotational constraints necessitate the growing of sugar beet crops on land that is known to be infested with rhizomania, you are advised to consult British Sugar about growing varieties considered to provide tolerance and a degree of resistance to the virus. If localised patches of infection have been identified within a field, it may be appropriate to consider not establishing a sugar beet crop in these areas.

If you suspect that rhizomania is present on your farm, you should consider appropriate application of those measures detailed above. You may also wish to approach British Sugar plc who will be able to advise you as to the preferred course of action.