Bacterial blight (Xanthomonas oryzae pv.oryzae)
Bacterial blight is chararcterised by two phases of infection Kresek and leaf blight Kresek is drying or wilting of the whole plant if affects the crop in early stages of growth in nurseries and upto 3-4 weeks after transplanting. The infected leaves become grayish green and begin to roll along the midrib and dry in severe cases the affected hills may be completely killed.
Leaf blight symptom start as water soaked lesions on the tip of the leaves and increases in length downwards along the margins. lnitially the lesions are pale green in colour and later turn into yellow to straw coloured stripes with wavy margins. Occasionally the linear lesions may develop any where on the leaf lamina or along the midrib with or without marginal stripes Lesions may cover the entire leaf blade. The bacterial blight disease can be confirmed by ooze test. Cut the affected plants at the base and dip it in a glass of water and hold it against the light for few minutes without shaking. From the cut ends white milky bacterial ooze will come out as streams.
Bacterial leaf streak (Xanthomonas oryzae pv oryzicola)
Narrow brownish yellow translucent interveinal lines joining to form large dirty white patches.
Note :
1. Spray fresh cowdung extract for the control of bacterial blight. Dissolve 20 g cowdung in one litre of water; allow to settle and sieve. Use supernatant liquid.
2. Application of bleaching powder @ 5 kg/ha in the irrigation water is recommended for checking the spread of bacterial leaf blight particularly in the kresek stage.
3. Before application of antibiotics for the control of bacterial blight, identify the disease by observing the bacterial ooze.
4. For control of sheath blight and sheath rot the following prophylactic measures may be adopted.
a) Apply neem cake-coated urea as recommended under fertilizer application.
b) Apply 50 per cent more potash than normal recommended dosage in split application.
c) Control weeds as suggested under weed control.
5. For control of sheath rot, spray the fungicides at the time of panicle emergence.
6. In organic farming, for the management of sheath blight of rice, spraying Azadirachtin 0.03 per cent EC or Azadirachtin 0.15 per cent w/w @ 2.5 litres/ha at the time of first disease appearance.
7. Spraying of any fungicide, preferably dithiocarbamate before the heading stage of the crop may be followed for the control of false smut and leaf scald diseases. Wherever control measures are adopted for sheath blight and sheath rot diseases, separate treatments are not needed for the control of leaf scald and false smut. Use 500 litres of water for high volume spraying and 200 litres for low volume spraying. It is advisable to use chemical on a rotational basis than using the same product continuously.