Bacterial leaf blight Of Rice

Bacterial leaf blight Of Rice
Xanthomonas oryzae pv. oryzae.

1. Mode of transmission/ dissemination: Strong winds and continuous heavy rains.

2. Period of occurrence: Tillering to Panicle Initiation stage.(June Jul to Sep-Oct).

3. Why and where it occurs: 

      The disease is mostly developed by presence of stubbles of infected plants and weeds. It can occur in both high and moderate temperature region, High temperature upto 25-30°C and below temperature 20°C. with relative humidity above 70%. The disease observed when strong winds and continuous heavy rains occur.The use of clipping tools for transplanting and by handling during transplanting can also prompt new infection.Severe winds, which cause damage, and over fertilization are suitable factors for the development of the disease.Bacterial blight can be severe in susceptible rice varieties under high nitrogen fertilization.Phosphorus and potassium deficiency and excess silica and magnesium also increase disease incidence.

4. Symptoms: The disease may appear in the following two phases viz.

    (i) Seedling wilt or kresek Phase:

Fig. : Bacterial Leaf Blight at Early Stage.

• One to two weeks after transplanting, the seedlings show systemic infection known as Kresek.

• Early symptoms appear as Green water-soaked layer along the cut portion or leaf tip of leaves.

• On seedlings, infected leaves turn grayish green and roll up.

• These leaves wither and float in water.Thereafter, the bacterium is carried through xylem vessels and becomes systemic and Entire plant wilt completely.

Fig. : Bacterial Leaf Blight at Maturity Stage.

• As the disease progresses, the leaves turn yellow to straw-colored and wilt, leading whole seedlings to dry up and  die.

• This symptom is often confused with damage caused by stem borer injury (dead heart) but the latter can be easily pulled out while rice plants with kresek are not easily pulled out from the soil.

    (ii) Leaf blight Phase: It is Most destructive phase

• Symptoms mostly seen 1-1.5 Months after transplanting.

Fig. : Bacterial  Blight on Leaf.

• Water-soaked to yellowish stripes on leaf blades or starting at leaf tips with a curly margin.

• drying of leaves back from tip and curling, leaving mid rib intact are the major symptoms.

• The leave of infected plant roll completely,Droop down and

• Severely infected leaves tend to dry quickly.

• The affected shoot may be completely killed in severe infection.

Fig. : Bacterial ooze test

 ⃣  To quickly diagnose bacterial blight on leaf:

    ⇨ Cut a young lesion across and place in a transparent glass container with clear water.

    ⇨ After a few minutes, hold the container against light and observe for thick or turbid liquid coming from the cut end of the leaf

5. Management:

     A. Preventive method:

• Use of disease free seeds.

• To treat seed with bleaching powder (100 g/l) and zinc sulfate (2%) reduce bacterial blight.

• Seed treatment with Streptomycin Sulphate And Tetracycline Hydrochloride 9:1 SP ( 90:10 SP) @ 1 Gm / 10 Lit Of Water for last 30 minute of sowing.followed by hot water treatment for 30 min at 52-54°C .

• Spray Azadirachtin 5% (50000 Ppm ) @ 2.5 Ml / Lit Of Water.

• Spray fresh cow dung extract for the control of bacterial blight. Dissolve 20 g cow dung in one litre of water; allow to settle and sieve. Use supernatant liquid. (starting from initial appearance of the disease and another at fortnightly interval).

    B. Cultural Practices:

• Grow disease resistance varieties (IR 20,72,Sasysree ,masuri, IR-54, IR-64, Ranjit ,Pusa 2-21, Ajaya, Khitish,Soshi,Renu,Asha and Daya.).

• Use of disease free seeds.

• Use balanced amounts of fertilizer,avoid excess N - application,

• Apply of potassium fertilizer as a top dressing to reduce the disease.

• Skip N - application at booting (if disease is moderate)

• Grow nurseries preferably in isolated upland conditions

• Destruction of collateral weed hosts

• Drain the field (except at flowering stage of the crop)

• Plow under rice stubble, straw, rice ratoons and volunteer seedlings, which can serve as hosts of bacteria.

• Maintain proper plant spacing.

   C. Chemical control:

• Spray Streptomycin Sulphate And Tetracycline Hydrochloride 9:1 Sp ( 90:10 Sp) @ 1 Gm / 10 Lit Of Water

• Apply of bleaching powder at the rate of 5 kg/ha in the irrigation water to check the spread of BLB especially in the kresek stage.

• Spray Copper Oxychloride 50% Wp @ 30 Gram + Streptocycline 9:1 Sp ( 90:10 Sp) @ 1 Gm / 10 Lit Of Water.

• Spraying fresh cow dung extract (20 gm cow dung is mixed in 1L water and allowed to settle and sieved).