Roxas City, the Philippines
August 20, 2008
by A. Lumaque
The Philippine Rice
Research Institute (PhilRice) has issued a warning against
bacterial diseases which attack rice farms as a result of
non-stop rains.
Bacterial leaf streak (BLS) is one of these diseases. It is less
invasive and popular than bacterial leaf blight (BLB) but it is
more prevalent "when it rains non-stop."
PhilRice plant pathologist Dr. Hoai Xuan Truong said BLS damage
ranges from 10 to 20% when most of the leaves are infected.
"Its symptoms are almost similar to BLB," said Dr. Truong. For
BLS, farmers should pay close attention to fine yellow lines on
the leaf surface. Almost half of the leaf will eventually turn
brownish and the tip will be droopy. In contrast, for BLB, up to
2/3 of the leaf becomes infected, yet the whole leaf remains
erect. In the field, a pronounced mass of rustic yellow color
above the canopy is a sign of BLS infestation," said a PhilRice
news release.
Scenes such as this are visible in some rice farms in Guimba and
other farms in Nueva Ecija.
Dr. Truong said, BLS infestation comes earlier than BLB. If
conditions like continuous rains are favorable, BLS signs become
visible 40-50 days after seeding (DAS).
He said that the first and best preventive option is to maintain
good drainage. This ensures that water will not stagnate in the
paddy.
In addition, water stagnation also prevents good aeration, which
eventually causes poor root development and lesser number of
tillers.
Planting of resistant varieties is another effective strategy,
according to Dr. Truong. PSB Rc82 and PSB Rc18 are some of the
varieties resistant to BLS. Dr. Truong cautions on planting
hybrid rice varieties during wet season, as most of these are
highly susceptible to BLS and other diseases. Dry season is the
best time to grow hybrid rice.
Dr. Truong further added that a variety resistant to BLB is also
likely to be resistant to BLS.
When copper-based fungicide application is the preventive option
taken, farmers must make sure to apply before 40-50 DAS. Beyond
that, it is useless to spray; chances are the bacteria must have
taken their place inside the leaf. One important consideration
in applying fungicide is that it must be done when it is not
raining. Otherwise, the fungicide will just be washed away
before it can even take effect.
Meanwhile, PhilRice plant breeders are developing lines
resistant to blast, BLB, and other rice diseases using both
conventional and biotechnology approaches.
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