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12
Jul
2013
Rice disease management reminders
Author: Yeshi Wamishe, Extension Rice Plant Pathologist

Sheath blight

It is still the time to scout for sheath blight.  So far, there have not been any alarming reports on sheath blight from any part of the state.  However, you need to watch out; it can move fast if the weather changes dramatically to its favor.

Blast

Blast has been reported on July 7, 2013 on CL261 in Arkansas, Monroe County (Photo 1).  Jupiter has shown some blast two weeks back in Woodruff County.  Continue scouting for this disease.  Keep the flood depth to at least 4 inches.  If you have to apply fungicides, remember timing is important to reduce damage from neck blast.

Photo 1 - typical blast lesion

Photo 1 – typical blast lesion

Autumn decline

 We still hear and see some fields with autumn decline/hydrogen sulfide toxicity/akiochi, also called black root rot.  See the yellow cast in the rice field (Photo 2) as an indicator for this situation.  Pull plants from the levee and bay and compare for possibility of this disease.  Note that a yellow cast does not necessarily mean your field has this disease.  For the short term, our recommendation is to “drain and dry” to aerate or oxidize the soil.  You need to use your judgment when you follow this practice.  Please read the previous blog articles at:  http://www.arkansas-crops.com/2013/05/23/weather-and-akiochi-disease-of-rice-is-there-a-link/and updates in the Rice Newsletter at:   http://www.arkansas-crops.com/2013/07/05/arkansas-rice-update-7-5-13/regarding this disease.  Long term, you need to start thinking about amending the soil, especially with potassium and zinc.  This problem requires tillage to allow oxygen in to the soil and you must work on your field to bring it to manageable size.  Large fields are difficult to manage this phenomenon.

Photo 2 - A plant with a yellowish cast may be indicative of autumn decline

Photo 2 – A field with a yellowish cast may be indicative of autumn decline

Pictured in Photo 3 are roots that appear healthy, but the crown is turning black.  We are not very sure about the cause; however, there are different speculations which we need to investigate.

Rice smuts

 Currently, most rice in the state is moving fast. Remember the prophylactic (protective) fungicide treatment for kernel and false smut. Timing and rates are both very important to suppress these late season diseases.  False smut is less sensitive to fungicides than kernel smut and hence, fungicide rates needed to be raised (for false smut). 

 

Photo 3 - Crown rot

Photo 3 – Crown rot

 

Photo 4 - Once heads have emerged, it's too late to spray for smuts

Photo 4 – Once heads have emerged, it’s too late to spray for smuts

 

 

 

 

 

 

 

 

 

 

 

Recommended Fungicide Rate to Suppress these smuts:

  • Use no less than 5.5 to 6 fl oz Tilt equivalent, 4 fl oz  is not good enough anymore.  For your information:
    • 19 fl oz Stratego has 5.5 fl oz Tilt equivalent;
    • 21 fl oz Quilt Xcel has 6.2fl oz Tilt equivalent;
    • 20 fl oz Quilt (old) has 5.8 fl oz Tilt equivalent.

Recommended Timing:

  • Early to mid-boot. If heads are emerging, it is too late (Photo 4)
  • Use as much water as possible, but at least 5 gal/A, to maximize coverage
  • Do not forget how high amounts of nitrogen fertilizer favors the smuts and most other rice diseases

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