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 .