Rice
Bacterial Blight of Rice
Xanthomonas oryzae pv. oryzae
Bacteria
In a Nutshell
- Grayish-green streaks on leaves.
- Yellowing and wilting of leaves.
- Milky ooze drops from the leaves.
Can also be found in
Rice
Symptoms
On seedlings, infected leaves first turn yellow to straw-colored and later wilt and die. On mature plants, the period of occurrence is mainly from tillering to panicle formation. Light green to grayish-green, water-soaked streaks appears first on leaves. As they merge, they form larger yellowish lesions with uneven edges. Leaves become yellow and gradually wilt and die. In the final stage of infection, milky bacterial ooze can be observed dripping from the leaves. These drops can later dry up and leave a white crust. This trait can help to distinguish this disease from the damage caused by some stem borers. Bacterial blight is one of the most serious diseases of rice.
Recommendations
Organic Control
To this day, no biological products are commercially available to the control bacterial blight in rice. The application of products based on copper can help to alleviate or reduce the symptoms but will not control the disease.
Chemical Control
Always consider an integrated approach with preventive measures and biological treatments if available. To combat bacterial blight, the treatment of seeds with an authorized antibiotic plus copper oxychloride or copper sulfate has been recommended. The use of antibiotics is severely restricted in some countries, so please check the measures in force in your country.
What caused it?
Symptoms are caused by the bacteria Xanthomonas oryzae pv. oryzae, which can survive on grass weeds or stubbles of infected plants. These pathogens are spread by wind and rain splash or irrigation water. Thus, disease incidence and severity are increased during bad weather (frequent rainfall, wind), high humidity (above 70%) and warm temperatures (25°C to 34°C). High nitrogen fertilization or close planting also favors the disease, particularly in susceptible varieties. The earlier the disease occurs, the higher the yield loss. When plants are infected during the development of the panicle, yields can be unaffected but a high proportion of the grains is broken. The disease occurs in both tropical and temperate environments, particularly in irrigated and rain-fed lowland areas.
Preventive Measures
- Use only healthy seeds, if possible from a certified source.
- Plant resistant rice varieties, this is the most efficient and reliable way to control the disease (and the cheapest!).
- Handle the seedling carefully during transplanting.
- Ensure proper drainage of the fields and nursery to avoid cross-contamination.
- Adjust nitrogen fertilizer applications to avoid excess and split the applications over the season.
- Apply an extra dose of potash along with the last dose of nitrogen when weather conditions are favorable.
- Avoid application of nitrogen in the form of urea.
- Destroy and remove weeds and alternative hosts from channels and surroundings.
- Plow under rice stubble, straw, ratoons and volunteer seedlings which can serve as hosts for the bacteria.
- Allow the fields to dry between the seasons in order to suppress disease agents in the soil and plant residues (fallow).
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