A
ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>
Date: 10 Jul 2007
Source: Mid-South Farmer [edited]
<http://midsouthfarmer.com/index.aspx?ascxid=fpStory&fpsid=29087&fpstid=2>
Temperatures in the mid-80s and low 90s [29 to 34 deg C], along
with high humidity have created the right conditions for sheath
blight, says Nathan Bruehling, Mississippi State University
Extension rice specialist.
Sheath blight is especially aggressive with cultivar 'CL-161'.
"We have more consistently seen a yield increase and economic
return when applying fungicide to this variety," Bruehling says.
'Cocodrie' is rated susceptible to sheath blight. "If sheath
blight can easily be found in the field and it has moved 4 to 6
inches [10 to 15 cm] up the plant, I would consider making a
fungicide application," Bruehling says. 'Wells' is rated
moderately susceptible to sheath blight. "I would scout and
monitor for sheath blight to make sure it is not aggressively
moving up the plant," Bruehling says. 'Hybrid' is rated
moderately susceptible to sheath blight. "I would monitor and
manage these hybrids similar to Wells," he says.
--
Communicated by:
J. Allan Dodds
Former ProMED-mail plant disease moderator <dodds@ucr.edu>
[Sheath blight on rice is caused by the fungus _Rhizoctonia
solani_ (current name _Thanatephorus cucumeris_.) It causes
lesions on sheaths of leaves near the water line during the late
tillering or early internode elongation growth stages. Lesions
expand and infection spreads rapidly in the field by runner
hyphae or plant-to-plant contact. Yield losses (up to 50 percent
in highly susceptible cultivars) result from poorly filled grain
heads and from reduced plant vigour. Fungal sclerotia survive
for long periods in the soil and float to the surface of flooded
rice fields causing infection in the next crop. The fungus can
also attack a number of weed hosts, which can serve as
reservoirs.
No reliable source of genetic host resistance has been
identified so far, despite the large number of lines and
varieties screened. No totally resistant variety, but many with
moderate resistance have been found. Related wild rices have
failed to provide sources of higher levels of resistance than
those found in cultivated species.
New high yielding, susceptible rice varieties requiring high
soil levels of nitrogen contribute to an increase in sheath
blight.
Nitrogen increases the susceptibility of plants further. Disease
management includes the use of less susceptible varieties,
avoiding close spacing of plants and excessive nitrogen
applications, control of grass and weed hosts, long-term
rotations with non- host crops, and foliar fungicides.
_T. cucumeris_ (_R. solani_) is a ubiquitous soilborne fungus,
which causes damping-off, root rot, basal stem root (foot rot),
and fruit rot in a large number of crops including citrus and
other fruit tree species, cruciferous and solanaceous
vegetables, legumes, cucurbits, peanut, soybean, canola,
lettuce, and a number of cereals. It is also the causal pathogen
of rhizoctonia root rot of wheat (see ProMED-mail post of 17 Jul
2007, no. 20070717.2291).
Map of US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>
Photograph of sheath blight symptoms:
<http://www.knowledgebank.irri.org/riceDoctor_MX/projectImages/image168.jpg>
Links
Sheath blight fact sheet:
<http://www.knowledgebank.irri.org/riceDoctor_MX/Fact_Sheets/Diseases/Sheath_Blight.htm>
Disease information:
<http://plantpathology.tamu.edu/Texlab/Grains/Rice/ricesb.html>
Information on disease management:
<http://www.knowledgebank.irri.org/RP/fungDiseases/sheathBlight/Management_Options.htm>
_R. solani_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=229666>
Current name _T. cucumeris_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=306777>.
- Mod.DHA]
[see also in the
archive:
Rhizoctonia root rot - Australia (SA) 20070717.2291
2004
----
Regulated plant pests, detection, March 2004: EPPO 20040710.1850
2002
----
Stem rot, rice - Australia 20020826.5152 Rhizoctonia oryzae,
pea, first report - N. America 20020516.4225
2001
----
Blackleg, root infection, canola - Australia (SA, NSW)
20010819.1959 2000
----
Melon root rot - USA (California): EPPO report 20001228.2290] |
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