Posts Tagged ‘herbicide injury’

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.

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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 June 7, 2010; blast, bronzing, herbicide injury, zinc

June 10, 2010

Blast lesions on Jupiter

These are blast disease lesions on Jupiter, but they could be on any variety.  Two points here, blast is present this year and Jupiter is susceptible.  To really control blast it will require two fungicide applications.  Read the fungicide label to determine the timing depending on which fungicide you use.  In general, the first application should be made during boot (approximately 4″ panicle) and then at about 50% heading.  That is an expensive treatment.

Bronzing in rice

It is unusual to have bronzing, a symptom of zinc deficiency, show up when it is warm and rice is older.  In this case the problem is induced by the high pH of the soils.  In the area they are known to be above 8 in many cases.  Even though the soil may test high in zinc it is not available because of the pH.  We recommended an application of zinc chelate or zinc sulfate to correct the problem.

Newpath injury to conventional rice

When the Clearfield system was introduced several years ago we were concerned about possible misapplications of Newpath to conventional rice fields.  While there have been a few reported cases of those situations most of the problems have been the result of drift from a Newpath application to Clearfield rice onto a nearby field of conventional rice.  The straw colored plants in this picture are already dead.

Newpath injury, single plant

The plant at right shows typical Newpath injury symptoms.  The growing point is killed resulting in a straw colored leaf in the center of the plant.  The oldest leaves are still green.  This is what we have learned to expect in Newpath drift onto conventional rice.

Newpath effects on growing point

If a plant like the one in the previous photograph are dissected lenghwise it will reveal dead or dying tissue.  The scientific term is necrosis.  Plants exhibiting this degree of injury will not recover.

Newpath injury without necrosis

In many instances the dose of Newpath is not enough to cause death of the plant, but the effects can be nearly as severe from a production standpoint.  In this case the growing point development is suppressed to the point that several axillary buds are developing.  In a normal plant as long as the growing point remains intact these buds never develop.  Even if these buds develops stems and eventually heads the heads will be smaller than normal and much later than normal.  The plant is competing with itself to produce grain as a survival mechanism.