Louisiana Rice: Disease Management Considerations

    Sheath blight in rice.

    Rice disease development varies due to the variety, or hybrid, you have chosen to plant, the presence of the disease pathogen, and the current environment for that pathogen to develop. The most common diseases in rice that we can use a fungicide to manage include blast, sheath blight, Cercospora (narrow brown leaf spot; NBLS), and smut (kernel smut and false smut).

    Scouting is an important in-season tool used to determine the presence and severity of rice diseases, particularly for sheath blight and blast.

    Scouting for diseases should begin early in the season. When scouting a field, make sure your disease evaluation is based on the whole field, not just a localized area. There is no easy way to do this. You must cover the entire field, making as many stops a necessary to check for present diseases.

    At each stop, you will want to evaluate if the disease is present on approximately a 3-foot section by opening the canopy. If you find disease, you may want to subjectively rate the severity of the disease from 1 to 10. A one rating would indicate that only one or two lesions were present, with a ten rating being a complete infestation.

    For sheath blight, cultivars that range from very susceptible to susceptible, will experience an economic loss of 5% to 10% of the tillers are infected during vegetative stages. For moderately susceptible cultivars, the level is 15%. At these levels, consider using a fungicide.

    For blast control, apply a foliar fungicide at early heading (50% to 70% heads emerging) when leaf blast symptoms are present. Leaf blast does not always precede rotten-neck blast, and preventive applications of a fungicide may be warranted if a blast-susceptible variety is grown. The best timing against Cercospora is between panicle differentiation and boot growth stages.

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    The later the rice is planted, the earlier the fungicide must be applied for Cercospora. Boot applications of the proper fungicides can reduce Kernel Smut or False Smut. Fungicide applications for smuts after boot split have little if any activity.

    Fungicide timing is critical for disease control. Growth stages change quickly, so it is important to scout for the rice growth stage while scouting for disease.

    Rice disease control using a single fungicide application is becoming more difficult because of the fungal resistance to fungicides, multiple diseases requiring different timings for effective control and higher multiple applications being warranted.

    Rice producers are encouraged to use full label rates, rotate modes of actions and use multiple fungicide applications when justified to effectively, and economically, manage rice diseases.

    Additional information on rice disease control can be obtained here.

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