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

August 20, 2010; Field Notes, flooding, Verification field harvest, leaf scald, leaf smut

September 9, 2010

Field ready to harvest flooded by heavy rain

A week before this picture was taken the field was drained and nearly dry in preparation for harvest.  Over 9 inches of rain fell within 24 hours flooding the field almost to the panicles.  This also caused about a fourth of the field to lodge.  The whole field was intended to be used for seed, but the lodged portion had to be sent to the mill.  It also caused the farmer to switch his equipment from rubber tires to tracks and change to a different header.

Burned leaf tips caused by Leaf Scald

In the last blog entry I said this was one of the worst years for Bacterial Panicle Blight.  That remains true, however it is also one of the worst for the incidence of Leaf Scald and Leaf Smut.  The tan to gray leaf tips give the field a scalded or burnt appearance.  The classic symptom of leaf scald is the inverted “V” pattern with a yellowish border between the dry and green leaf tissue.

Leaf Smut of Rice

Leaf Smut, like Leaf Scald is seldom a serious disease of rice.  We always see it show up late usually after the field has been drained for harvest.  It looks like someone sprinkled the leaves with black pepper.  After the field is drained the upper plant parts begin to die resulting in a loss of defense mechanisms and the onset of several diseases.  This year the pressure was about the worst I have ever seen and may have contributed to the complaints about unsatisfying yields from what appeared to be “good rice”.

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.

July 26, 2010, Field Notes, brown spot, sprangletop, glyphosate injury

July 28, 2010

Brown Spot Disease in a Rice Field. Photo by K. Fontenot

Brown spot disease of rice is often associated with nutrient problems.  In this field the pattern of the disease reflects that because the disease is most severe where in the process of land leveling more top soil was removed.

Glyphosate Injury to Rice Panicles

In other images of glyphosate injury posted on this blog there has been more distortion of the grains and the flag leaf.  In this field the drift event occurred late when panicle development was fairly advanced.  The primary symptoms visible here are sterile grains.  Little grain or panicle distortion is evident, but the effect is dramatic.

Severe infestation of Sprangletop in a rice field. Photo by N. Hummel

A combination of factors including possible herbicide resistance led to this severe infestation of a rice field by Tighthead (Amazon) Sprangletop.  Sprangletop is one of the most difficult to control grass weeds in rice production.

Field Notes, July 19, 2010, Glyphosate Injury, Sheath Blight, Brown Spot

July 22, 2010

Glyphosate Effects on Rice Panicles

 

When glyphosate drifts on to rice when rice is in the boot stage symptoms are seldom noticed until the crop begins heading.  In this case drift was suspected on several ages of rice.  When stems of plants in early boot were split these deformed panicles were found.  Note that in the panicle at left one kernel is developing normally while all others are not.

Herbicide Injury to Rice Growing Points

 

Again splitting stems exposed dead or severely injured growing points of these rice plants.  Herbicide injury is suspected.  Plant samples were taken to try to determine the causative agent.  Glyphosate and Newpath are the current suspects.

Brown Spot of Rice

When I first saw the sypmptoms shown here and the pattern in the field I thought gramoxone had drifted on the field.  That was quickly eliminated when a survey of surrounding vegetation showed no injury.  History of the field provided a clue.  The farmer had laser leveled the field in the spring.  Brown spot is a disease often assoicated with nutrient deficiency and that is the likely cause here.

Sheath Blight on Rice Panicles

 

When sheath blight of rice is severe it moves up the plant rapidly.  From the flag leaf sheath it will then infect the panicles resulting in one of the most severe forms of the disease.  When this level of disease is prevalent in a field major yield reductions can be expected.  Fungicides applied earlier could have prevented it.

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.

Field Notes, July 2, 2010, Chinch bugs, Gramoxone injury, Straighthead disease

July 8, 2010

chinch bug injury to rice paniclesLast week I mentioned chinch bug injury to seedling rice.  Normally if chinch bugs are a problem they affect seedling rice that is not flooded.  By this time of year we do not expect to have chinch bug problems.  In this case panicles were injured by overwhelming numbers of chinch bugs in the panicles.

Adult chinch bugs appear to have a white spot on their back which is actually the tips of its wings that are folded over its back.  Chinch bugs have piearcing -sucking mouthparts.  They literally suck the juices out of the plant.  If only a few insects were present injury would likely not be noticed.  In this case the panicles were loaded up with chinch bugs.

Immature chinch bugs are bright red and wingless.  They feed the same way the adults do, by sucking sap out of the cells.  As they grow they become darker.  Most of the time we ingnore them when they are found at this stage of growth, but in this case the injury was significant and the field was to be sprayed to control rice stink bugs anyway so an insecticide that would control both was applied.

Gramoxone injury looks much worse than its effect on rice when it drifts on to rice.  While the spotting causes the field to look burnt and heavily spots the leaves, it is a situation where “what you see is what you get.”  When new leaves emerge they will be fine.  Heavy spotting of flag leaves could cause a problem, but it would have to  be severe.

Straighthead Disease in Rice

 

Straighthead disease of rice gets its name from the failure of grains to fill and the consequent upright appearance of the panicles.  Because there is no grain development the panicles do not nod over; they remain straight.  It is a physiological disorder, not a disease caused by a plant pathogen.

"Parrot beaking" of spikelets

One of the more obvious symptoms of straighthead is the distorted spikelets commonly called “parrott beaking”.  Similar symptoms can be observed when glyphosate drifts on to rice past internode elongation.  Many times there is no indication of drift until the heads emerge.  Some varieties are more prone to straighthead than others.  If straighthead has occurred in a field it is likely to occur again so a resistant variety should be selected.

Normal Flag Leaves on Straighthead Affected Plant

 

One way to separate straighthead from glyphosate injury is to examine the flag leaves.  If the problem is straighthead the flag leaves are normal in size and configuration.  In the case of glyphosate injury the flag leaves will be greatly shortened and are often twisted as well.  Panicles are also shortened when affected by glyphosate but are of normal length if the problem is straighthead.

Field Notes, June 28, 2010, Cercospora, chinch bugs

July 8, 2010

We used to call this disease Narrow Brown Leaf Spot, but because of its confusion with Brown Spot and the devastating impact it had several years ago we now refer to it as Cercospora.  Cercospora is the genus name of the fungus that causes the disease.  These symptoms tell us infection has already occurred, but is not the yield limiting phase of the disease.

This is  a close-up of some of the same leaves shown in the first photograph.  One major characteristic of this disease is the linear brown spots on the leaves.  They follow the veins of the leaves.  The phase that causes the most yield damage is the net blotch phase that shows up on the sheath of the flag leaf and on the stem.

Most of the time chinch bugs are a pest when they feed on young seedlings in rice fields that are not flooded.  Once the fields are flooded we usually forget about chinch bug injury to rice.  In this case seedling rice was being flooded late in the year and chinch bugs were reducing stand.  We expect the flood to take care of the problem.

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.

Field Notes June 21, 2010; Colaspis, crazy rice, guttation, spider mites

June 23, 2010

This is the adult of the Colaspis beetle whose grub feeds on the roots of rice.  It was called the Grape Colaspis until entomologists determined it is not that species.

Until the actual identity of this rice plant can be determined I am calling it “crazy rice”.  It is much taller than the CL151 in which it was found, it is glabrous (smooth), and the lemma (the big half of the hull) is awned.  It does not fit any of the descriptions of wild rice I have studied.

As mentioned in an earlier post, this is the first time I have seen spider mites in rice.  In this image several are visible.  I think if you click on the image you can enlarge it.  Stuart Gauthier, county agent in Vermilion parish found them in one field along an edge.  Initially I lost the actual sample, but we returned to the field and confirmed them.

This year a lot of fields were flooded later than is recommended.  In this case it also meant nitrogen fertilzer was applied later than recommended.  The combination of establishing permanent flood late and delaying nitrogen application caused the yellowing of the lower leaves visible in this field.  The plants are also shorter than they should be at this stage of development.

Water of guttaton always makes a good photograph.  It is caused by the buildup of water pressure in the plant beginning late in the evening and continuing until early morning.  After daylight photosynthesis begins, the stomates open and a water deficit begins to occur in the plant.  At that time the droplets may actually be drawn back into the plant through the pores called hydathodes at the margins of the leaf.  More often they just evaporate or fall off the plant.


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