Reviewed March, 2009

Rice Disease Management

Allen Wrather and (573-379-5431), Gene Stevens,
University of Missouri-Delta Center

Most rice diseases can be managed to minimize losses. The four most important strategies for rice disease management are to rotate crops, to plant resistant varieties, to plant in warm soil and to use fungicides when necessary. An integrated approach that uses all of these methods is the most effective and profitable.

Resistant varieties: Varieties immune to all or most rice diseases do not exist. However newer varieties often have improved levels of resistance. Growers should choose varieties based on MU yield trials in their area and resistance to locally important diseases (Click here for a list of resistant varieties).

Crop rotation: Rotating crops will help manage several diseases of rice.

Planting in warm soil: Seedling diseases of rice are accentuated when the soil around the seed and seedling is cool and wet. Seed and seedling death can result in severely reduced stands and consequent reduced yields. Growers should avoid planting in cool soil and when the weather forecast indicates that cool conditions may develop within several days of planting. Seed should be treated with a fungicide prior to planting (Click here for list).

Foliar Fungicides: Scout rice fields for blast and sheath blight symptoms from internode elongation to 90 percent heading. If symptoms are found, prepare to use a foliar fungicide (Click here for a list of labeled foliar fungicides). Timing of foliar fungicide application to rice is essential for best disease control.

Additional information: An accurate diagnosis of plant disease is essential before selecting a management technique. Whenever possible, consult an expert in plant disease diagnosis. This guide is not intended to aid identification of rice diseases, but is intended to be a rapidly accessible source of information on management techniques.

Other MU publications have more information on rice disease identification and management. They are: MP 645, Rice Blast: Identification and Control and MP 646, Rice Sheath Blight Control. These publications are available from the Delta Center, Missouri Agricultural Experiment Station, P.O. Box 160, Portageville, MO 63873, or may be available at your local Extension center and are on the World Wide Web (aes.missouri.edu/delta).

These publications were made possible through the efforts of many others, including Joyce Elrod, senior research technician at the MU Delta Center.

Disease and Pathogen Symptoms Control/rate Remarks
Black sheath rot
Gaeumannomyces graminis
Dark brown-black discoloration from the crown up the stem. Leaves of heavily infected sheaths die. Tillering and yield may be reduced. Click here for foliar fungicides Usually only a problem in fields during the first few years rice is grown. Some cultivars are more susceptible than others.
Blast
Pyricularia oryzae
Gray, football-shaped leaf lesions with brown margins. Leaf symptoms are rare. Nodes and panicles are darkened. When panicle infection occurs, heads will be white. The panicle may collapse. Click here for foliar fungicides Worse when rains occur frequently and temperatures are above 80oF. Plant for a stand of 15 to 20 plants per square foot. Apply nitrogen at the time and rate recommended. Maintain flood to 4-inch depth. Avoid susceptible varieties. See MU publication MP 645.
Brown spot
Cochliobolus miyabeanus
Small oval to circular, brown leaf lesions. Infected heads are blackened. May be confused with kernel smut. Fingers will not be discolored when kernels are handled, as with kernel smut. Click here for foliar fungicides Occurs on plants stressed by low temperature, herbicide injury, other diseases and nitrogen deficiency. To control, prevent plant stress that may retard growth.
False smut
Ustilaginoidea virens
Infected kernals turn into a "smut ball". It will first appear orange. Older smut balls are olive-green to brown and may be up to 1/2 inch across. Click here for list of foliar fungicides. Tilt applied at boot will suppress this disease. To minimize this disease: 1) plant clean seed, 2) Treat seed with a fungicide, 3) Avoid late planting, 4) apply Tilt at boot, 5) apply recommended rates of nitrogen.
Kernel smut
Tilletia barclayona
Minute, black masses of spores inside the hull burst the hull and are then visible. Hands are blackened by the spores when the kernels are handled. Click here for foliar fungicides Worse during warm, rainy weather at bloom. Apply recommended rates of nitrogen. Losses are seldom severe.
Seedling disease
Rhizoctonia, Pythium and Fusarium spp.
Dead or weakened seedlings, discolored roots and thin stand. Click here for seed treatments Plant high-quality fungicide treated seed in a well-prepared seedbed. Plant for a stand of 15 to 20 plants per square foot.
Sheath blight
Rhizoctonia solani
Gray-green lesions with red-brown border near water line. Lesions may be small at internode elongation and later extend up the stem. Click here for foliar fungicides Worse when humidity is high and temperatures are 90oF. Yield loss can be severe. Plant for 15 to 20 plants per square foot. Plant least susceptible varieties. Follow recommended nitrogen rate and timing. See MU publication MP 646.
Sheath spot
Rhizoctonia oryzae
Similar to sheath blight, but symptoms are confined to the sheaths. Occurs in patches a few feet in diameter. Click here for foliar fungicides Occurs rarely. Avoid planting Lemont and Gulfmont in fields with a history of this problem. Application of fungicides may help.
Stem rot
Sclerotium oryzae
Small black lesions on leaf sheath near water line. Stems can be rotted and lodge. Dark gray mold and small black particles that resemble powdered charcoal can be seen inside stems. Click here for foliar fungicides Apply proper rates of potash and nitrogen. Avoid highly susceptible varieties.


* Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Ronald J. Turner, Director, Cooperative Extension Service, University of Missouri and Lincoln University, Columbia, Missouri 65211. * University Extension does not discriminate on the basis of race, color, national origin, sex, religion, age, disability or status as a Vietnam-era veteran in employment or programs. * If you have special needs as addressed by the Americans with Disabilities Act and need this publication in an alternative format, write ADA Officer, Extension and Agricultural Information, 1-98 Agriculture Building, Columbia, MO 65211, or call (573) 882-8237. Reasonable efforts will be made to accommodate your special needs.

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