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Rice blast overwintered in Louisiana: Review of management options for Arkansas
Author: Yeshi Wamishe, Extension Rice Plant Pathologist

A report came from Louisiana on February 21, 2013 that rice blast lesions were found on new rice sprouts growing from the stubble. Reportedly, this field had severely infected rice in 2012. According to Dr. Don Groth of LSU, the pathogen is actively sporulating due to the warm moist environmental conditions. There is fear that another blast outbreak may happen earlier in the season in 2013.

Louisiana had a severe blast epidemic in in 2012.  It is likely that the fungus overwintered on volunteer rice plants that were not freeze-killed due to the mild winter, providing an early source of spores to infect emerging rice seedlings. However, there is more than one survival mechanism for the blast pathogen.  The pathogen is seed-borne as well as air-borne.  Air-borne spores usually infect young leaves; spores from young leaves infect collars, nodes, and panicles of rice plants. Although blast is not as common in recent years as sheath blight, when present, it can cause dramatic yield loss on susceptible rice varieties – up to 100% under the right conditions. Severe damage occurs when the fungus attacks nodes found below the head causing “neck blast”.

Although Louisiana had problems with blast in 2012, Arkansas did not. We observed a susceptible variety in one county with severe damage that was mediated somewhat with flood management and fungicides; a couple of other fields in another county with heavy tree lines had damage.  Overall, blast pressure in our state last year was light. Where available, resistant varieties are a good option to manage the disease on fields with a history of blast.  Currently, hybrids appear to have the best overall resistance, but several Clearfield and non-clearfield varieties have adequate resistance to be easily managed under Arkansas conditions.  Please see our latest ARPT report for ratings prior to seed purchase.

The rice blast pathogen can survive on seeds and can easily be moved. In addition, resistance is not permanent as the blast fungus eventually adapts to overcome resistant varieties if planted over and over under favorable blast conditions. In summary, the following are Best Management Practices for rice blast disease, and are primarily recommended for fields with a history of blast problems:

  1. If seed of a susceptible variety is to be planted into a field with a strong history of blast disease, then the use of azoxystrobin (Dynasty®) fungicide at the labeled rate for seedborne blast should be considered.
  2. If possible, simply select and plant resistant varieties in fields with history of blast or that are difficult to water.
  3. Plant early,depending on the weather, to avoid the likelihood of heavy blast pressure late in the season. Planting over a range of time during the early planting window is also recommended to spread the risk of all rice developing at the same time.
  4. Fields with heavy tree lines, especially on the east side – which prolongs night-time dew period – are more likely to develop blast so these should not be planted with susceptible varieties.
  5. Use the recommended fertilizer rate. High nitrogen in fields with blast history makes susceptible varieties prone to the disease.
  6. Know your soil types and grow rice in fields where a deep flood can be maintained. Maintain a consistent >4 inch flood especially on susceptible varieties at all times.
  7. Scout fields starting early in the season (June) for leaf blast symptoms on susceptible varieties in particular.
  8. If leaf blast is seen, be prepared to apply preventative fungicides at heading. Usually fungicides are applied on susceptible varieties at late boot stage to 10% heading followed by a second application at 60-90% heading.  However, you should refer to the current label for the product used to be sure.  Remember that heading is not the same as “headed”, that is during heading the neck is still in the boot and it is essential to treat the field before the neck comes out of the boot to maximize the effectiveness of current fungicides.  The most common mistake that leads to fungicide failure to reduce neck blast is waiting too late to apply.

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