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19
Aug
2016
Rice disease update: Rain exacerbating late season pressure
Author: Yeshi Wamishe, Extension Rice Plant Pathologist

By Yeshi Wamishe, Extension Rice Pathologist

Temperatures have been moderate with frequent rain in this couple of weeks.  Some rice diseases were also in progress.

Sheath Blight

Late season sheath blight in fungicide untreated plot.

Fig.1. Late season sheath blight in fungicide untreated plot.

Sheath blight still continues to move up in untreated fields likely causing some late season damage (Figure 1). You may be seeing heavy production of sclerotia by the fungus as a means of its survival for the next crop season.  Grain fill often completes prior to the loss of the upper two leaves and its effect on yield may not be alarming as long as these two leaves are not heavily damaged.

Neck and Panicle Blast (Figure 2a and 2b)

Fig2NeckBlast

Fig. 2a. Neck and flag leaf collar blast with blank white head.

Conditions appear favorable for blast development although we did not get reports of blast this week.  Reports from last week included what will ultimately be substantial yield losses where no fungicides were applied or where the application was mis-timed.

 

Bacterial Panicle Blight (BPB)

This disease has been a concern after the rain started while the day and night temperatures were high. A few commercial fields were reported with noticeable disease pressure.  We have seen substantial BPB in experimental fields at Rice Research and Extension Center near Stuttgart, AR.  BPB symptoms (Fig. 3a, b) are noticeable shortly after the panicles fully tip over in the field and become

See the discoloration on the lower portion of most of the florets for one of BPB symptom. Panicle branched are green unlike in blast disease.

Fig. 3a. See the discoloration on the lower portion of most of the florets for one of BPB symptom. Panicle branched are green unlike in blast disease.

 Panicle blast blanks some panicle parts.

Fig. 2b. Panicle blast blanks some panicle parts.

more noticeable as grain fill is completed.  Panicles with BPB mostly can be blank and do not tip over.  However, some florets with BPB disease may be distributed across the panicle and panicles may still tip over.  Some other panicles may have blanks at the lower third or half of the panicle and may only tip over slightly.  In the latter two situations, the presence of BPB may not even be noticed.

 

Kernel Smut (Figure 4)

We have seen some kernel smut in rice after the rain started.  Kernel smut symptom is more obvious when kernels swell from moisture due to rain or morning dew.  The black spores ooze out as they are pushed by moisture in rice kernel.  Rice fields with history applied with heavy nitrogen fertilizers often show considerable kernel smut in susceptible rice cultivar. 

Panicles with sever BPB disease do not tip over at grain filling.

Fig. 3b. Panicles with sever BPB disease do not tip over at grain filling.

False smut

We have seen false smut in a couple of fields last week.  Rain and lower temperatures favor false smut disease development.  Similar to kernel smut, rice fields with history applied with heavy nitrogen fertilizers often show considerable false smut in susceptible rice cultivar under favorable conditions.

Sooty molds

Sooty molds affect the appearance of rough rice and lower the quality of bran.  Sooty mold symptoms are caused by opportunistic fungi that colonize rice panicles during wet, humid weather.  Molding often is severe when harvest is delayed or if the crop lodges to the ground.

Sooty molds are superficial and do not affect milled rice.  The surface of kernels is blackened and you may also see black spores on the leaves.  Sooty molds have

Panicles with BPB after saprophytic microbes’ invasion later in the season.

Fig 3c. Panicles with BPB after saprophytic microbes’ invasion later in the season.

been confused with kernel smut in the past, but they are easily identifiable.  Sooty mold is superficial but kernel smut is internal.  If a kernel has sooty mold, once the hull is removed the kernel should not be discolored to any great extent and should also be whole.  While if it is kernel smut, the kernel will be partially or completely filled with black spores.  Both sooty molds and kernel smuts problems may result in black discolored equipment during harvest (Figure 6).  However, heavy kernel smut fields will have severe yield losses and also may be darker combine harvesters.  So, exceptionally high yields and intense kernel smut do not go together.

Fig. 4. Kernel smut severity comparison between panicles from fungicide treated (left) and untreated fields (right).

Fig. 4. Kernel smut severity comparison between panicles from fungicide treated (left) and untreated fields (right).

 

False smut galls at the end of the season.

Fig. 5. False smut galls at the end of the season.

 

 

 

 

 

 

 

Black discolored equipment during harvest can be heavily covered by sooty molds spores and sometimes are confused with kernel smut.

Fig. 6. Black discolored equipment during harvest can be heavily covered by sooty molds spores and sometimes are confused with kernel smut.


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