Field Notes June 14, 2010; black rice bugs, spider mites

June 14, 2010

Symptoms of spider might injury to rice leaves

The narrow white spots on the leaves of this rice plant are mostly a result of spider mites feeding on the leaves.  Some of the white scars are the result of rice water weevil feeding.  In general the spider mites cause more frequent lesions and they are a little more rounded at the ends than those caused by the rice water weevil.

Spider mite feeding signs on rice leaves

A closer view of the feeding signs of spider mites on rice leaves reveals more detail.  Most of them are more rounded at the tips than those of the rice water weevil.  In some cases the areas are only faintly white.  The rice water weevil feeds by actually chewing away the leaf cells leaving the lower epidermis and cuticle intact creating a sort of “window pane” effect.  Spider mites essentially suck the juice out of the cells causing dehydration.

The yellowish object in top center of the photo is a spider mite


In this image a single spider mite can be seen on a rice leaf.  They are larger than the panicle rice mite.  While they have been reported in greenhouses before this is my first time to see them on plants collected in the field.

Greatly magnified image of a mature and an immature spider mite


The image at right is a greatly magnified image of two of the spider mites found on rice leaves.  The mite on the left is an adult and the one on the right is immature.

Louisiana black rice bug injury symptoms


Each year for the past several we have seen an increase in the incidence of this type of injury.  It resembles stalk borer damage, but is not from a borer.  It is infrequent, but fairly common.

"Louisiana" black rice bug adult


We originally called this insect the black rice bug until we were told that common name was already assigned to another species.  Until we have an official common name we are referring to it as the “Louisiana” black rice bug.  When it feeds it causing firing of leaves often more on one side of the mid vein of the leaf than the other.

Beetle and feeding signs on rice leaf


Dr. Natalie Hummel found this beetle (yet to be identified) feeding on rice leaves in Madison parish.  It causes symptoms that resemble those left by feeding of rice water weevils.  She noticed lots of feeding signs without the presence of heavy populations of rice water weevil that would have been expected.

Beetle feeding on rice leaf


This is a close up of the beetle Dr. Hummel found feeding on rice leaves.  When she has a positive ID of it I will update the blog.


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.

Field Notes May 31, 2010; borers, algae, salt injury

June 8, 2010

Midrib damaged by rice stalk borer

Usually we find borers in the stem of the rice plant, but in this case a borer had entered the midrib of the leaf.  The first instars of the borer are small enough to bore into the midrib.

Early instar rice stalk borer

The rice stalk borer can be distinguished from the Mexican rice borer by the color of its head capsule and the lines on its back.  The head capsule of the Mexican rice borer would have been a lighter brown and the lines on its back would be broken and appear as a series of dashes.  Here it is clear the rice stalk borer has a dark head capsule and the lines on its back are continuous.

Algae (scum) in rice

Most of the time an algal bloom causes problems in rice especially if it is young.  In those cases wind can push the layer of algae over the top of seedlings and literally starve them of sunlight.  When an algal bloom occurs in older rice it can be beneficial because it will shade out weeds underneath it.

Salt injury to rice

The inverted “V” pattern on the leaf tip is indicative of some sort of nutrient toxicity.  This pattern used to be common in corn when we used to side dress it with high rates of potassium fertilizer.  In that case it was usually a temporary problem.  We checked the well being used to irrigate this field and found high levels of both sodium and chlorides and total soluble salts.  The field had been flushed and flushing aggravates salt problems.

Field Notes May 24, 2010; localized decline, zinc deficiency, bronzing

June 7, 2010


Lime induced zinc deficiency

Localized decline

The two photographs above show similar field symptoms and the two following show similar symptoms on leaves of rice plants.  Both exhibit zinc deficiency sypmtoms, but for different reasons.  In the first field the problem was induced by an application of lime to a previous soybean crop.  In the case of Localized Decline we know that zinc is deficient but we do not know exactly why it happens.  Plants affected by Localized Decline will also have high levels of iron and aluminum in them.

Lime induced zinc deficiency symptoms

Zinc deficiency associated with Localized Decline

Field Notes May 17, 2010; thrips in rice, iron toxicity, zinc

June 7, 2010

Thrips damage in rice

The light flecking on the leaves shown at right are due to thrips.  Thrips have a rasping mouthpart so they sort of sand off the surface causing dehydration.

Thrip on rice leaf

The black object above the pencil point is a thrip on a rice leaf.  Thrips are seldom a problem in rice, but in some parts of the state and in some years they can cause significant injury.  Usually it is when it is very dry.

Iron deposits in rice field

Most of the well water in Louisiana contains some iron, but in this case the well used to irrigate this field had an excessive amount of iron in it.  The levels were high enough to coat the plants and to cause a toxic reaction.

Iron toxicity on rice seedlings

The seedlings shown here had heavy deposits of iron on them and were exhibiting toxicity symptoms.  Because high rates of zinc have been used to counter iron uptake associated with the phenomenon called Localized Decline a heavy dose of zinc chelate or zinc sulfate was recommended.

Field Notes May 10, 2010; Prowl injury, hybrid rice, red rice

June 4, 2010

Prowl effect on root tips

Prowl is an excellent herbicide in rice, but it can cause some root pruning.  The injury shown here is minimal and rice will grow out of it.

Broadcast seeded rice

Even though the equipment was supposed to be top notch, something was clearly wrong here.  The heavy population of rice is in the area of overlap.

Volunteer resistant rice

Between the drill rows is a heavy population of volunteer rice composed of red rice and volunteer hybrid rice.  Both are apparently resistant to Newpath because one application has already been made.

Newpath resistant rice seedlings.

Rice seedlings shown in the photograph at right are all apparently resistant to Newpath herbicide.  Left to right they are: planted variety, volunteer with some susceptibility, resistant volunteer, resistant red rice.  The field has a history of both red rice and hybrid rice and successive rice crops.

Field Notes April 29, 2010; dayflower, fall panicum, hemp sesbania, jointvetch, Texasweed

June 4, 2010

Fall Panicum ligule

At right is a photograph of the ligule of Fall Panicum.  It technically is membraneous but fringed with hairs.

Fall Panicum leaf surface

The upper leaf surface of Fall Panicum is glabrous, that is, it has no hairs.  Sometimes literature simply refers to a smooth leaf when hairs are absent.

Pubescence on lower surface of leaf

The lower surface of the leaf at right has pubsecence on it.  The seedline looks like Fall Panicum, but Fall Panicum is not supposed to have these hairs.

Pubescence on leaf sheath

The leaf sheath of the same seedling is also hairy.  This is a 4 leaf seedling which might have some bearing on the problem.  I will monitor this plant later in the season to see if it is indeed Fall Panicum or another species.

Jointvetch seedling

The Jointvetch seedling at right can be separated from Hemp Sesbania because its first true leaf is compound.  A compound leaf is one composed of tiny leaflets instead of a single blade.  Leaves like the ones at right are said to be pinnately compound.  Pinnate means they resemble a feather.

Hemp Sesbania seedling

At right is a Hemp Sesbania seedling.  The two leaves pointing left and right are actually seed leaves or cotyledons.  The first true leaf points toward the top of the photograph.  Unlike the second true leaf which points down, the first true leaf is simple.  All other leaves will be compound.  This characteristic of the first true leaf is a reliable tool to separate Hemp Sesbania from Jointvetch.

one leaf Dayflower

When it emerges from the soil Dayflower resembles a grass seedling.  However, there is no clear cut collar at the base of the leaf and the leaf has a fleshy texture.

Texasweed in cotyledon stage

Texasweed is known by several common names including Mexican weed.  The two leaves shown here are not true leaves, they are seed leaves or cotyledons.  Often herbicides do not work well on it in this stage.

Field Notes April 19,2010; allelopathy, barnyardgrass, signalgrass, jointvetch

June 4, 2010

Parasitic wasp and aphids

  At left center is a tiny wasp.  I had a visitor riding with me last week and he saw the thing without magnification.  I had to use my hand lens.  As a size reference the two brown, somewhat spherical objects are aphids.  The wasp is one that parasitizes the aphids by laying its eggs in the aphid.  The brownish color of the aphids indicates they have already been parasitized. 

Jointvetch seedling

At left is another review photograph.  The seedling shown here has two cotyledons (seed leaves) and two true leaves. Both true leaves are compound thus it is Jointvetch. If the the first true leaf had been simple it would have been Hemp Sesbania. Remember simple leaf, Sesbania. 

Ligule of Broadleaf Signalgrass

Barnyardgrass has no ligule

Hairy sheath of Broadleaf Signalgrass

Barnyardgrass is smooth

Above is a set of four photographs.  The two on the left side of the page are of broadleaf Signalgrass while those on the right are of Barnyardgrass.  Both were about 3 leaf seedlings.  If you follow the leads in the Schematic Diagram for Seedling Weed Identification in Rice you will note the presence or absence of a ligule will separate these two weeds.  If Fall Panicum was included in the photographs it would have to be separated from Broadleaf Signalgrass on the presence or absence of pubescence.  The ligules of these last two can be very similar, but the hairs on the lower surface of the leaves of Signalgrass distinguish it from Fall Panicum.

Ryegrass in rice field

Ryegrass is allelopathic toward rice.  The word describes the ability of one plant to suppress the growth of another.  In this instance the allelopathic plant is ryegrass and the plant being suppressed is rice.  In no-till studies years ago Dr. Pat Bollich discovered a great deal of diversity between cover crops and their allelopathic effects.    Ryegrass is strongly allelopathic to rice.  As long as it is green and for a few weeks following its death rice growth will be suppressed. 

If I had been asked to do stand counts in the field shown in the three photographs below I would have said the stand was too thick.   In the second photo lanes created by burning the stubble from last year reveal two things: first, burning stubble does not produce enough heat to really control weeds; second the stand is very uneven. 

The real surprise is that this rice was not planted – at least not this year.  Last year a non-Clearfield hybrid was planted in this field.   Enough rice shattered from the second crop to produce this crop.  Clearly a lot of seed made it to the soil and the dormancy of hybrids helped the seed to survive. 

Volunteer rice seedlingsField view of volunteer riceStand of volunteer rice

Field view of volunteer rice

Volunteer rice seedlings

Field Notes April 12, 2010; seed midge, barnyardgrass

June 3, 2010

The photograph above was taken in lower Vermilion parish last week.  At the time it was the largest rice I had seen this year.  It was water seeded and a pinpoint flood management system was being employed.  The combination of cooler than normal temperatures and dry conditions has really delayed crop development.  In almost every case I have seen where the grower flushed following dry seeding the crop is ahead of those fields where the grower decided to “wait on a rain.” 

In the last issue of Field Notes I discussed soil cracking associated with seed bed preparation in a flooded field.  The photograph here was taken by Eddie Eskew.  It demonstrates a classic case of “potato chipping”.  On the right side of the photograph you can see the obvious curling and the white sandy surface of the ped of soil left below it.

In the photograph at left are small tubes made of soil and something like spider web stuff that insects produce.  These are protective structures of midges, including the rice seed midge.  .

The photograph at right is for review.  The genus Echinochloa which contains barnyardgrass, jungle rice and their variants is the main genus of grasses that lacks a ligule.

Field Notes April 1, 2010; DD50, drill seeding, heat units

June 3, 2010

If you visit the AgCenter’s web site, you can access weather data that offers some explanation for the slow movement of rice this year.  On the left side of the home page is a block with the title Services.  Weather is within that block.  I looked at growing degree days.  A growing degree day (GDD) for rice is calculated by adding the daily high and daily low then dividing by 2 (this provides a type of average temperature for the day) then subtracting 50 from that number.  For example if the high was 71 and the low was 46 there would be 8.5 GDD accumulated that day. [(71 + 46) ∕ 2 = 58.5.  58.5 – 50 = 8.5.]   

I took a look at weather data from March 2009 and 2010.  In 2009 there were 5 days in March where no heat units were accumulated, 9 days when 15 to 19 heat units were accumulated, and 5 days when more than 20 GDD units were accumulated.  In contrast, this year there have been 5 days of no heat units, 1 day between 15 and 19 units, and 0 days with more than 20 heat units.  I repeat, it’s just too cold. 

Below is a photograph I took in one of our verification fields last year.   Note the seed furrow on the right.  It is not closed properly and this was made by one of the best drills on the market.  The problem is in certain soil conditions we are asking too much of the machinery.  When the soil moisture is at a certain level the soil will not crumble so the press wheels cannot close the furrow properly.  

The next photograph on the next page shows what often happens when silt loam soils are prepared in a flooded state.  They crack or “potato chip” as some refer to it.  

It happens because a thin layer of sand forms about an inch from the surface as sand particles settle out before the silt and clay fractions.  The very fine sand will not prevent the movement of water downward due to the pull of gravity, but it can prevent moisture movement UPWARD due to capillarity.  As the upper half inch of so of soil dries by evaporation from the surface the barrier of sand prevents upward movement of water.  Soil below the sand can only dry by gravity while the upper layer dries by both gravity and evaporation.  That causes the upper layer to contract more than the layer below and cracks develop.  If it continues to shrink the edges curl upward causing “potato chipping”. 

The following photograph was sent in by Stuart Gauthier, county agent in Vermilion parish.  It shows a field worked in water and drained.  I’ll try to get a photograph of the sand layer I described above.

Cracking of the soil surface