A disease is an impairment of the normal physiological functioning of a plant or plant part. It interferes with its normal structure, condition, and economic value. Diseases are considered major constraints in rice production. Rice diseases are mainly caused by bacteria, fungi or viruses. Here are the common and most severe diseases in rice and their management. A rice farmer should be aware of the proper diagnosis for these diseases in order to avoid yield loss and poor quality produce.
Bacterial leaf blight is prevalent in both irrigated and rainfed conditions particularly during the wet season. Xanthomonas oryzae, a bacterium causes this disease. It may live in seeds, plant residues, perennial hosts, or in paddy soil and water and survive in infected rice stubble, in plant debris, or in soil if the host tissue is not decomposed.
- On seedlings, infected leaves turn grayish green and roll up.
- As the disease progresses, the leaves turn yellow to straw-colored and wilt, causing the whole seedlings to dry up and die.
- Kresek/Wilting on seedlings may sometimes be confused with early rice stem borer damage. To distinguish kresek symptoms from stem borer damage, squeeze the lower end of infected seedlings between the fingers.
- Kresek/Wilting symptoms should show yellowish bacterial ooze coming out of the cut ends. Unlike plants infested with stem borer, rice plants with kresek (wilt) are not easily pulled out from soil.
- Planting resistant varieties has been proven to be the most efficient, most reliable, and cheapest way to control bacterial blight.
- Ensure good drainage of fields (in conventionally flooded crops) and nurseries.
- Keep fields clean. Remove weed hosts and plow under rice stubble, straw, rice ratoons and volunteer seedlings, which can serve as hosts of bacteria.
- Allow fallow fields to dry to suppress disease agents in the soil and plant residues.
Blast, a fungal disease, is found in both upland and lowland environments and thrives on areas where water deficiency is prevalent, night humidity is high, and night temperature is low. It is caused by Magnaporthe grisea, the rice blast fungus which can cause lesions. Blast occurs in all phases of the plant’s growth.
- Initial symptoms appear as white to gray-green lesions or spots, with dark green borders.
- Older lesions on the leaves are elliptical or spindle-shaped and whitish to gray centers with red to brownish or necrotic border.
- Some resemble diamond shape, wide in the center and pointed toward either end. Lesions can enlarge and coalesce, growing together, to kill the entire leaves.
- Plant varieties that are resistant to blast.
- Avoid late planting.
- Plant as early as possible within the recommended planting period.
- For leaf blast, re-flood if field has been drained.
- Maintain flood at 4 – 6 inches to ensure soil is covered.
Rice tungro disease is caused by the combination of two viruses (Rice tungro bacilliform virus/“RTBV” and rice tungro spherical virus/“RTSV”), which are transmitted by leafhoppers. It causes leaf discoloration, stunted growth, reduced tiller numbers and sterile or partly filled grains. Tungro infection can occur during all growth stages of the rice plant. It is most frequently seen during the vegetative phase. Plants are most vulnerable at tillering stage.
- Tungro-infected plants show symptoms of stunting, delayed flowering, reduced number of tillers, small and not completely exerted panicles, and partially filled grains, covered with dark brown blotches.
- Mottled young leaves; older leaves are yellow to yellow-orange.
- Once a rice plant is infected by tungro, it cannot be cured.
- Grow tungro or leafhopper resistant varieties.
- Practice synchronous planting with surrounding farms.
- Delayed or late planting, relative to the average date in a given area, makes the field susceptible for Tungro.
- Plow infected stubbles immediately after harvest to reduce inoculum sources and destroy the eggs and breeding sites of green leaf hopper.
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