Posts Tagged ‘Bacterial Panicle Blight’

Field Notes, August 31, 2010; heat effects, verification yields, stink bugs

September 16, 2010

The past three weeks I have had several calls with the same basic theme; “Why are my yields falling off?”  The simple answer is heat.  It has been much too hot especially at night for successful pollination and grain fill.  This has also led to more Bacterial Panicle Blight than we have seen in several years.  Even second crop is being affected because temperatures have remained high throughout most of this month and a lot of second crop rice is or has already flowered.

I have also had questions about pecky rice.  Normally we associate pecky rice with rice stink bug damage and secondary damage from fungi that enter through the wound made by the stink bug.  This year there have been instances where there did not appear to be heavy stink bug populations, but pecky rice was reported.  There is no simple explanation for this.  Again I suspect excessive temperatures and disease are playing a role.

Other callers have asked about late season stink bug control. My philosophy on stink bugs is to make a final sample at the time of drain recommendation.  If I encounter a hatch out or have been sitting on a 2/3 threshold for a couple of weeks, I will recommend a spray because it will be two to three weeks (if everything goes right) before harvest and during that time the numbers are only going to go up.  Not everyone agrees with this practice. I hate stink bugs. We did exactly that in one verification field that had already been sprayed once and I’m glad we did because rain delayed harvest so that there were 4 weeks between drain and harvest.  Stink bugs were still present at harvest. I hate to think of what the numbers would have been if we had not sprayed. It was also a seed rice field which helped to justify the additional spray.

Below is a table summarizing yields from the Rice Research Verification Program this year. It was a much smaller program with only three fields involved; however it was as challenging a year as any.  In spite of the problems I was surprised at how little difference in yields we experienced between this year and last year.  I suspect if we had 9 fields this year the differences would have been greater.

Parish Acres Variety Cwt/A green Bbl/A green Bu/A green Cwt/A dry Bbl/A dry Bu/A dry
Avoyelles 41.8 Cocodrie 85.63 52.9 190.3 80.57 49.7 179.0
Jeff Davis 35.8 CLXL745 91.04 56.2 202.3 87.38 53.9 194.2
St. Landry 31.3 CL111 73.46 45.3 163.2 71.71 44.3 159.4
Average     83.91 51.8 186.5 80.26 49.5 178.4
                 
2009     86.06 53.1 191.3 81.31 50.2 180.7
2010-2009     2.15 1.3 4.8 1.05 0.7 2.3
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August 5, 2010; Field Notes, Newpath injury, panicle blight

September 9, 2010

Newpath injury on sheath

The panicles shown in the photograph were victim of Newpath drift.  Newpath is applied to Clearfield rice to kill non-Clearfield rice.  When it drifts it can cause serious injury.  In this case the injury was minimized because it was not extensive and it hit rice at a less susceptible stage.  Many of the panicles did not fully exsert from the flag leaf sheath.

Grain germinating on panicle

Some of the panicles that failed to exsert from the flag leaf sheath flowered and formed grains down in the sheath.  The grain shown here is germinating.  After it ripened the captured moisture caused it to germinate.  This one was found after splitting open a flag leaf sheath.

Bacterial Panicle Blight on CL261

This year has been one of the worst in terms of the occurrence and severity of Bacterial Panicle Blight.  This disease attacks rice when high nighttime temperatures occur during flowering.  Apparently the spikelets in the middle of the panicle were flowering under a period of high night temperatures while the uppermost and lowermost florets flowered under more favorable conditions.  This is an example of why flowering is spread out over about a week in each panicle beginning at the top and progressing downward.  It is a survival mechanism.

Field Notes, July 12, 2010, Bacterial Panicle Blight, Panicle Blast, Potassium Deficiency, Tip Burn, Herbicide Injury

July 22, 2010

Late Season Potassium Deficiency

I have been told that some folks in Arkansas refer to this problem as “Arkansas high yield disease” because it is almost always associated with high yields. We saw it last year mostly in CL151 and that has been the predominant variety again this year.  The most distinctive symptoms are the narrow brownish lesions between the leaf veins.  Leaf analysis last year indicated a potassium deficiency.

Unknown tip disease

From the pickup truck fields affected with this problem might resemble those affected by potassium deficiency, but they are not the same.  This problem has characteristics of leaf scald and bacterial leaf streak.  Again they are not the cause.  We do not know the cause.  Dr. Groth has been unable to isolate fungi from it.  Because it is in fields also showing Bacterial Panicle Blight the question is whether this is another manifestation of the disease.  We don’t know.

Bacterial Panicle Blight

The symptoms at right are of Bacterial Panicle Blight.  It has been around for a number of years.  At one time we thought it was an environmental problem because it is almost always associated with high night-time temperatures.  The typical symptom is the brownish discoloration of the kernels while the panicle branches remain green.  Because it is caused by a bacterim, fungicides are of no benefit.

Panicle Blast

Rice blast is a well known disease that reportedly is especially severe in Arkansas this year.  It can be distinguished from Bacterial Panicle Blight by the dried, brown panicle branches.  It is caused by a fungus thus fungicides are of benefit when applied at the correct time and at the right rate.

Shortened internodes and adventitious roots caused by herbicide injury

When a consultant brought stunted plants to me the first thing I did was split the stems.  It was clear the internodes were much shorter than they should have been at that stage of development.  It was probably caused by herbicide applied to the field.  We visited the field a week later and it is producing normal panicles.  Maturity is delayed and plants are shorter.  Impact on yield is uncertain.

Stacked nodes versus normal internodes

 

In this photograph the plant at right shows normal internode elongation while the one at left has the stacked nodes (shortened internodes) typical of the plants shown in the first photograph.

Command injury on Jazzman rice

 

One of the early questions about culture of Jazzman was its potential susceptiblity to Command herbicide.  I did not have a good answer until this year.  The field where this injury was observed was adjacent to a field of a long grain variety that showed no symptoms.  The reaction of Jazzman apparently is similar to that of the medium grain varieties which are more sensitive to it.

Rice Stink Bugs, Narrow Brown Leaf Spot, Cercospora, Panicle Blight

June 23, 2010

Yesterday we found lots of rice stink bugs in one of our verification fields.  Other folks out checking headed rice said they are finding them too.  If rice is headed they should be checked for stink bugs by sweeping with an insect sweep net.  We had more than one insect per sweep which is more than 3 times the threshold value.

We also found Narrow Brown Leaf Spot which is caused by Cercospora janseana.  At least two varieties were involed, CL161 and CL151.  Because of the confusion with Brown Spot the disease has been commonly called Cercospora to differentiate the two.  It requires propiconazole containing fungicides to control it.

In this heat we are also setting up for an outbreak of Bacterial Panicle Blight which will not be evident until grain development begins.