2007 - Texas A&M AgriLIFE Research Center at Beaumont - Texas ...

Although commercial long grain rice varieties lack
significant levels of resistance to stem rot, the newer semidwarf
varieties tend to be more tolerant to stem rot because
of their resistance to lodging.
Currently registered fungicides do not adequately
control stem rot and are not recommended for this purpose.
Quadris ® and Tilt ® , when applied for sheath blight, can
moderately suppress stem rot.
Crop rotation and reduced rates of nitrogen fertilizer in
fields with a history of stem rot are recommended control
practices.
Narrow brown leaf spot
Narrow brown leaf spot, caused by the fungus Cercospora
janseana, causes more yield and grain loss than is often
suspected. The fungus attacks the leaf, sheath, uppermost
internodes and glumes.
On leaf blades, it causes short, linear, narrow, brown
lesions parallel to the leaf veins. As plants approach maturity,
leaf spotting can become severe on the more susceptible
varieties and result in severe leaf blighting and premature
death. Infection of the leaf sheaths result in a large brown
blotch or “net blotch.”
The fungus also can cause a “neck blight,” where the
internodal area above and below the node at the base of the
panicle becomes light brown to tan. The affected area dies
and the kernels in the lower portion of the panicle fail to fill.
Low nitrogen levels seem to enhance the disease.
Tilt ® , Quadris ® , Stratego ® and Quilt ® fungicides applied
in the mid- to late-boot stage have been effective in suppressing
the diseases caused by C. janseana.
Table 16. Fungicides for rice foliar disease control.
Material
Gem 25WG
Moncut 70WG
Rate/A and timing
8.0–9.8 oz @ PD-5 days to
late boot
8–16 oz @ PD AND PD+
10–14 days
Sheath blight
control 2
7.5–8.0
7–7.5
Moncut 70WP 11–16 oz @ PD-5–10 days 6
Propimax 10 f. oz @ PD to PD+10 days 5
Quadris
Quilt
Stratego
9.2–12.3 fl oz @ PD+5 days
to late boot
14–34.5 fl oz @ PD+5 days
to late boot
14–19 fl oz @ PD+5 days to
late boot
8–8.5
7.5–8.0
7–7.5
Tilt 10 fl oz @ PD TO PD+10 days 5
1
See product label for details on application rate and timing.
2
Sheath blight control ratings 0–9.: 0 = no control; 9 = very good
control
Some other rice diseases for which fungicides have shown some efficacy
include:
Stem rot: Quadris 9.2–12.8 fl oz/A at PD to mid-boot.
Kernel Smut: Tilt or Propimax 4.0–6.0 fl oz/A at late boot.
Blast: Quadris 12.2 fl oz/A or Gem 6.4 to 9.8 oz/A at late boot and again
at early heading when 50 percent of the main tillers have panicles 70
to 80 percent of their length emerged but with the panicle bases yet
unexposed. If only one fungicide application is used, the early heading
application is often onsidered the preferable one.
Panicle blanking complex
Florets that do not pollinate or fill properly can result
from of a number of biological and environmental factors.
Often “blanked” florets can be numerous and result in significant
yield losses. Completely empty florets indicate that
they never successfully pollinated.
Research at Texas A&M and the International Rice
Research Institute (IRRI) has shown that temperatures
above 95 degrees F during the pollination process (anthesis)
cause floret sterility. Another high-temperature sensitive
period that can cause pollen sterility occurs about 10 days
before pollen shed.
Early planting may be one way to reduce heat-induced
sterility. Heat sterility should not be confused with the disease
called panicle blight.
With panicle blight, florets often are pollinated but
developing embryos abort, leaving a small embryo or undeveloped
seed between the glumes. Upon close observation a
few days after panicle exertion, a lack of luster in the green
glumes of the affected panicle can be noticed. Within 1 to 2
weeks, the glumes turn various shades of tan to light brown
and lack the turgidity and brightness of healthy glumes.
Two important characteristics of panicle blight separate
it from other panicle disorders:
• Panicle blight often does not appear to prevent
successful pollination; and
• The rachis or branches of the panicle remain green for
a while right to the base of each floret, even after the
glumes dessicate and turn tan.
Pollination takes place and a small grain begins to
form, but it aborts and remains small and underdeveloped.
Research shows that panicle blight is caused by a bacterium,
Burkholderia glumae. Varieties with California germplasm,
such as Cypress, Maybelle and Cocodrie, seem to be
more prone to serious damage by panicle blight.
Currently, the best way to manage panicle blight
involves the use of timely planting, proper varietal choice
and avoiding excessive seeding and nitrogen rates. The
copper-based product Top-Cop ® applied at 2 quarts per acre
at late boot has suppressed panicle blight in field tests, but
foliar phytotoxicity has been reported. If used, it is best to
apply Top-Cop ® when the foliage is dry and without use of
a surfactant.
Ear blight is a disease complex caused by several fungi,
including those that cause narrow brown leaf spot (Cercospora
janseana) and brown leaf spot (Cochliobolus miyabeanus).
These fungi can cause discoloration and blight of
the uppermost internodes, the neck below the panicle, the
branches of the rachis, and spikelets of the panicles. This
often results in poorly developed grains.
Tilt ® , Quadris ® , Stratego ® and Quilt ® applied in the midto
late-boot stage help suppress this disease complex.
Black sheath rot
Black sheath rot or crown sheath rot is caused by the
soil-borne fungus Gaeumannomyces graminis var. graminis
and has been in Texas rice fields for at least several decades.
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