BLAST DISEASE (Nov 25, 2013)

2 . Symptoms  and damage :
- On the  leaf: disease damages mainly the seedling stage - tillering . Initially, lesions are only small dots ,
blue gray color , then   become  bigger  with typical  lozenge  shape  ,  brown edge, gray white center ,
on   infected  varieties , lessions are very  large  , however; on the   resistant  ones , l
esions are  needle points  .When lesions  become severe,lesions gather to  make  leaves  dry burnt  .
- On the  leaf neck , stem and  panicle neck  ,  initial symptom also  has blue gray color  ,
switches  to brown color  later because  fungus  attacks on vascular  impeding  the transport of nutrients ,  
feeding  leaves, stems and seeds , so it makes  leaves ,  stems break ,   seeds unfilled    early   , empty late
- On seed : disease occurs in blossoming stage , lesion on seeds also has  typical  shape above  ,
 brown edge   , white gray center . If the disease attacks  soon  , will  make  seeds  empty  .

3 . Pathogens :
Disease  caused by fungus ,  its scientific name  is Pyricularia oryzae or P. grisea , the fungal spores are very small ,
can fly  far  , disease  is easily widespread   . Fungal spores grow well in the cool temperatures of 24-28 degrees C ,
high humidity above 80 % , so if the climate cool , sunny morning alternating rainy afternoon , foggy weather  are  suitable for disease  to occur .
Therefore,  disease usually occurs in Winter Spring  crop. Fungal spores beside absorbing   nutrients in the rice plant ,it  also secretes   toxic substance  of Pyricularin ,
  causes toxcicity  to plant . Beside rice plant , the fungus  also remains  weed species such as  Echinochloa sp,  Leptochloa sp ,  Cynolon dactylon  , ratoon rice

4 . Environmental conditions :
- Weather: as mentioned above , if the night is cold , the day time is  hot ,  rain alternating shine , high humidity , early morning ,
late evening, there is much  fog on the field , it is favorable for disease to occur .
- Susceptible varieties .
- Density of sowing : the thicker  sowing  is , the denser rice canopy becomes    , the higher humidity in  the field is  . Disease  favorably  occurs  .
- The dryness  on the field     : The field  lacking of water  causes  plant  poor growth ,  weak  disease resistance, disease easily occurs  .
- Fertilizing : fertilizing NPK unbalancedly  , fertilizing nitrogen in excess , fertilizing  nitrogen  late  , spraying nitrogeous foliar  feed  especially  booting and blossoming stages   ...
that  causes disease easily  or severely .
- Source  of    disease fungi   : Source  of    disease fungi    have persisted in the straw , weeds , seeds ... as well as elements spreading through the next  crop  .

5 . Stages that note blast disease :
Seedling stage , the disease is most likely to  occur , especially infected  species  weaken and influence  yield later
End of tillering  to  and booting stages
Before and after  blossoming  stages .
At these stages , we should note to  visit the field  regularly  , wading into  the field  and observing  each cluster of rice plants ,
especially  where rice plants grow well , densely ,  are usually  in the middle of the field  , near borders  , sluices,  if any , treatment should be done immediately .

6 . Prevention
For prevention and treatment of blast  disease ,  we need to use general measures :
- The use of resistant varieties or half resistant ones ,. When choosing varieties , we need to combine  
the blast disease resistance and  hopper resisting  characteristics  to suit local conditions  so as to 
give  high yield and good quality . When choosing varieties , we  should consult the  agricultural  extension agency in locality
- Ensuring that  chosen  varieties  is   weed seed and disease free , varieties should be  treated before sowing .
- The  quantity of varieties  for  medium  sowing  is around  80 -120 kg  per ha  ( depending on the locality ) , not thick sowing .
- Fertilize  NPK balancedly  , not  use too much nitrogen fertilizer or fertilize  nitrogen late, nitrogen quantity about 80-100 kg N / ha is sufficient .
Nitrogen should be used on  its need  , we  can use comparison table  for rice leaf color to fertilize .
When disease occurs, it should stop fertilizing or spraying  foliar feed  with nitrogen .
- After harvesting  it should  plow  to inter the straw  to return  the organic substance  to the soil  .
- Field sanitation , killing rice that is  grown by seed left  from previous crop  ,  ratoon rice  ,
clear up weeds  at the border where pathogens exist and spread later .
- Keep the water level in the field to suit each growth  need of rice plant   ,  avoid dry field when  the disease occurs .
- Make forecast plot  , earmark few square meters in the same of rice field ,  thicker sowing  ,
fertilize more nitrogen to forecast early disease that occurs  for timely prevention.
- Agro chemicals : the following  specific products  can be used :
o Trizole 75WDG , 20WP
o Lua Vang 20WP
o  Ki Saigon 10 H, 50ND
o Py Saigon 50 WP
o  If  disease is severe  ,  possible combination of broadcasting  Ki Saigon 10 H  and spraying   Trizole or Lua Vang
Noting that spraying  plenty  of water is necessary when spraying product ,  product   makes sure that  plants become  wet evenly ,
we can spray early in the morning when it  has  no dew or cool late afternoon . To prevent panicle neck  blast especially infected varieties ,
the  rice field 5-7 before  blossoming , it should  spray one time  after  rice blossoming evenly , it will  be sprayed  the second time .