It is still a little early to know how bad diseases will be in 2015. But in general, disease pressure is higher this year in Louisiana than in 2013 and 2014. Even with the cold winter, blast got an early start on CL151 and Jupiter.
Most of the fields with severe leaf blast lost their floods sometime after permanent flood. Fungicide use was high with most susceptible varieties treated with at least a single heading application. It appears that most of these applications were effective in suppressing blast, except in a couple of situations where rain occurred soon after application or a different mode of action fungicide with poor blast activity was used.
Sheath blight did not develop to severe levels, even with all the rain we received during the early season, and most fields were treated for sheath blight. Exceptions were in areas where strobilurin fungicides were used, and the fungicide-resistant sheath pathogen was apparently present. Indications are that the strobilurin-resistant sheath blight pathogen continues to spread to new areas.
The new fungicides, Sercadis and Convoy, which have a different mode of activity, were effective against the resistant fungus, and producers were generally satisfied with the control. The consensus is that sheath blight is becoming more of a problem on hybrid varieties, and fungicide applications have become more common.
Because of a lack of extreme day and night time high temperatures in early 2015, bacterial panicle blight did not develop extensively as in previous years, except in isolated incidences. Bacterial panicle blight was severe in fields planted with Jazzman 2, which is very susceptible. Recent high temperatures in mid-July will put late-planted rice at risk. The good news is that the same high temperatures are severely limiting further sheath blight and blast development. No effective chemical control agents are available for BPB.
Cercospora was present but light in most fields in 2015, except in a few fields. Fungicide applications were not as effective as anticipated in isolated fields, and higher rates and multiple applications of propiconazole-containing fungicides may be needed. Fungicide timing should also be adjusted with earlier applications the later rice is planted. Cercospora will probably be severe in the second crop if weather conditions are favorable (wet) in the fall.
Unfortunately, no fungicides are labeled for second crop, and propiconazole is not that effective in controlling Cercospora in the second crop. Stubble management – including rolling, mowing and stubble removal – are effective at reducing Cercospora in the ratoon crop. Leaf blast due to lack of water.