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23
Jul
2014
Disease alert: Rice blast throughout Arkansas
Author: Yeshi Wamishe, Extension Rice Plant Pathologist

The weather this season is favorable to cause a blast epidemic. Get ahead of the disease! Rice blast pathogen spores can easily move across a field and/or from a field to another by wind. Clay, Randolph, Lawrence, White, Prairie, Lonoke, Woodruff, Monroe and Arkansas Counties have all had reports of rice blast largely on Jupiter followed by CL151 with a couple of cases on Roy J, CL152 and Caffey. The blast pathogen attacks leaves, nodes, the collar, the neck, and panicles of rice plants. The worst of all is neck blast. Neck blast (neck rot) may cause near 100 percent yield loss unless checked by fungicides. Seeds treated with fungicides do not guarantee neck blast control throughout the season. Planting a resistant variety is the best control method. However, it does not guarantee lasting control of blast since the pathogen population (race) dynamics could alter. Planting early also may not guarantee full control of blast if the variety is susceptible, weather is favorable, and field conditions are encouraging for pathogen growth, reproduction, and spread.

Field conditions that favor blast:

  1. Fields with heavy tree lines, especially on the east side – which prolongs night-time dew period – are more likely to develop blast if planted with susceptible varieties.
  2. Soil types where a deep flood cannot be maintained are more prone for blast disease.
  3. High nitrogen in fields with blast history makes susceptible varieties prone to the disease.
  4. Fields with history are likely to get the disease if planted with susceptible varieties.
  5. Fields in river bottoms with longer dew periods are prone for the disease.
  6. Fields low in potash and low irrigation capacity favor disease development.
  7. Low cut fields when leveling get low in fertility, particularly potash.

Weather conditions that favor blast:

  1. Frequent light rains that allow extended leaf wetness
  2. Extended cloudy days that allow slower leaf drying
  3. Slow winds that transport spores and slow leaf dryness
  4. Warmer days and cooler nights that allow long dew periods

What to do in the year like this:

  1. Scout fields starting early in the season for leaf blast symptoms on susceptible varieties. The disease could be severe in late planted rice.
  2. Get the disease diagnosed correctly. Incorrect diagnosis could be costly.
  3. Maintain a consistent > 4 inch flood especially at all times until it is time to drain.
  4. If leaf blast is seen, be prepared to apply preventative fungicides. Leaf blast mostly can be suppressed by maintaining flood depth. In severe cases, fungicides application may be required. For neck blast protection, fungicides are applied on susceptible varieties at late boot stage to 10% heading, followed by a second application at 50-75% heading. Heading refers to the heading of the main tillers. Approved fungicides need to be applied before heads have emerged. Remember that heading is not the same as “headed.” During heading, the neck is still in the boot. See pictures below for timing of fungicide application.
  5. If only one heading application is to be risked, research has shown the best timing as when the main tillers have panicles about 1/3 – 1/2 of the way out of the boot (but the bottom 2/3 to 1/2 still down in the boot).
  6. The higher labeled rates of fungicides are most effective on this disease.
  7. Refer to the current labels for handling and restrictions of the approved fungicides. The labels are the rules. To read more on fungicide timing, rate and contents for major rice diseases including blast go to http://www.arkansas-crops.com/2014/07/11/fungicides-diseases-contents/.

The most common mistake that leads to fungicide failure:

  1. Waiting too late to apply fungicides
  2. Using the wrong products.
  3. Using reduced rates of the fungicides.
Correct timing for the 1st fungicide application against neck blast

Fig. 1 – Correct timing for the 1st fungicide application against neck blast

Fig. 2 - Correct timing for the 1st fungicide application against neck blast

Fig. 2 – Correct timing for the 2nd fungicide application against neck blast

Fig. 3 - Incorrect timing for fungicide application against neck blast: Once the head is out of the boot, it is too late!

Fig. 3 – Incorrect timing for fungicide application against neck blast: Once the head is out of the boot, it is too late!


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