Rhizomania, also called “root madness" or "crazy root,"
has caused significant losses in root and sugar yield. First described in
Roots and leaves
The most obvious symptom of rhizomania is a mass
of fine, hairy secondary roots that consists of a mixture of dead and healthy
roots. The mass of secondary roots often is most evident several inches below
the crown. Early season infection may result in severely stunted fleshy roots.
In some infected plants the taproot has a nearly normal crown diameter but is
severely restricted two or three inches below the soil surface resulting in a
"wine glass" shape. Vascular tissue is visibly darkened in
longitudinal sections of infected roots. Leaf symptoms are most often a general
chlorosis (yellowing) that may reveal scattered
infested areas in a field, but other problems can depict similar symptoms. Veinal yellowing and necrosis (the result of systemic
infection) is diagnostic of rhizomania but is
extremely rare in this region.
Beet necrotic yellow vein virus (BNYVV) is the causal agent of rhizomania. Polymyxa betae, a soilborne fungus, is the vector of BNYVV and carries the
virus from diseased to healthy roots. Sugar beet is a host to both the fungus
and the virus. Clusters of thick-walled resting spores contain the virus. The
resting spores and the virus particles contained inside them can survive well
over 15 years in the absence of a suitable host. The resting spores germinate
in the presence of sugar beet roots. Motile zoospores emerge from the resting
spores and carry the virus through free moisture in wet soil to the roots of
sugar beet. The zoospores enter root cells and release the virus particles and
infection of the root cells by the virus occurs. The optimum soil temperature
for infection is 23-27 degrees C (73-81 degrees F). Since free moisture is
necessary for zoospore movement through soil, frequent irrigations or rainfall
favor new infections.
Diagnosis of rhizomania cannot be based solely on
visual symptoms. Instead, an ELISA test, or enzyme linked immunosorbent
assay, is used. This is a serological test that may require two days to
complete. A positive ELISA test indicates that BNYVV is present. A negative
test indicates that BNYVV, if present, was not detected. Positive tests are
confirmed by another test, i.e., western blot. False negative tests may result
due to a number of factors. Good sampling procedures are critical. Root samples
should include new fibrous root growth, occurring soon after rainfall or
irrigation, and samples should arrive at the laboratory within one day after
collection. Chances of detection are improved if several roots are submitted
for a sample. Roots should be dug to at least a depth of 10-12 inches.
Testing laboratories use a bioassay test of soil samples from fields to be
planted to sugar beets. Sugar beets are grown in test soil for six to eight
weeks and the roots collected and tested by ELISA for BNYVV. Soil samples
should represent no more than 40 acres and should consist of 2 quarts of soil composited from at least 20 subsamples
of soil tube cores taken from the upper 6 inches of the soil profile.
Quarantine laws will require that specific sampling procedures are used before
fields qualify as rhizomnia-free. State departments
of agriculture should be contacted for assistance when phytosanitary
certificates are needed for shipment of various kinds of produce, i.e., seed
potatoes, etc., to states with rhizomania quarantine
laws.
Laboratory Tests for BNYVV
Testing fresh roots of suspect rhizomania
infected sugarbeet plants and soil samples from
fields to be planted to sugar beets will permit growers to identify infested
fields and allow them to make more effective management decisions related to
cropping practices and containment.
Currently available rhizomania tolerant or resistant varieties perform satisfactorily in infested fields, especially when used in combination with soil fumigation with Telone II. Nematicidal rates of Telone II used in nematode infested fields are within label rates for rhizomania.
Fungicidal Treatment
Telone II soil fumigation at label rates for rhizomania will suppress the disease, apparently by
controlling the soil-borne fungus vector, Polymyxa betae. The best control is attained with
a combination of Telone II soil fumigation and
tolerant or resistant varieties.
Sanitation may be most practical for delaying long distance contamination.
To protect uninfested farmland, prevent or limit the
movement of infested soil into uninfested fields.
Shared farm equipment should be thoroughly cleaned of clinging soil before
entrance into uninfested fields. Returning tare dirt
to fields provides a source of movement of small quantities of infested soil
long distances into uninfested fields. Movement of
contaminated machinery or livestock directly into a production field can easily
move enough infested soil to contaminate a field with the infected vector
fungus.
Early Planting
Early planting when soil temperatures are cooler, and use of production
practices that result in rapid establishment of the plant canopy, will reduce
risk of yield loss.
Soil Moisture
Manage soil moisture to minimize
or eliminate the need to irrigate during the first six weeks after seed
germination. Avoid over-irrigation or excessively wet soil.
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Products for suppression of rhizomania: |
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Nematicide
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Rate
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Preharvest interval, remarks
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Telone II Soil FumigantR |
10-18 gal/A broadcast equivalent |
Preplant interval: 1 wk + 1 wk/10 gal applied |
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RRestricted use pesticide. 1Labeled for chemigation |
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The information herein is supplied with the understanding that no
discrimination is intended and that listing of commercial products, necessary
to this guide, implies no endorsement by the authors or the Extension
Services of
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Categories: Sugarbeets, Diseases, Viral diseases, Rhizomania, Root madness, Crazy root
Date: