by: Dustin Harrell

Louisiana Rice Notes – 5 – PDF

Blast found in Jupiter

Many things have happened over the past couple of weeks in regard to the Louisiana crop.  Probably the most important is that leaf blast has been identified in two Vermilion Parish rice fields.  Both fields are growing the medium grain variety Jupiter, which is considered moderately susceptible to blast.  One field is approximately at the mid-tillering growth stage of development and the other is almost at green ring.  With the early sighting of leaf blast in Jupiter many questions have arisen regarding fungicide applications for blast.  The most often asked questions are: How bad does the leaf blast have to be before deciding to trigger a two fungicide application strategy to control the blast?  If you do decide to apply two fungicide applications, what timings are recommended?  These are excellent questions, and Dr. Groth has quickly put together information regarding these blast questions plus a whole lot more…

Leaf blast has started to show up in the area on the variety Jupiter. Blast disease is caused by the fungus Pyricularia grisea and is one of the most important diseases of rice in the world and the Mid-South. Yield losses as high as 90 percent have been observed in Louisiana because of this disease. Blast can infect rice from the seedling stage to near maturity. The leaf blast phase most commonly occurs between the seedling and late tillering stages. Leaf spots start as small white, gray or blue-tinged. They enlarge quickly under moist conditions to either oval or diamond-shaped spots or linear lesions with pointed ends with gray or white centers and narrow brown borders. Leaves and whole plants can be killed under severe conditions. The most important aspect of leaf blast is that it provides inoculum for infecting the panicles. Fungicides are not normally used at this stage unless you are losing the stand. The best control method is to restore or deepen the flood so all of the soil in the field is covered with water.

Scouting for blast should begin early in the season during the vegetative phase and continue through to heading. Scout the entire field, examining plants at several different locations. Blast is more commonly found in fields where (a) the field has a history of disease, (b) the variety is susceptible, (c) high nitrogen rates are used, (d) the field has sandy soils, (e) the rice was planted late (late-planted rice is more likely to encounter foliar disease problems than early-planted rice), (f) along the edges of tree lined fields, most importantly (g) the rice is growing under upland (no flood) conditions. Draining for straighthead and water weevil control may increase the incidence and severity of blast. These conditions should be avoided whenever possible. Also, as the percentage acreage of blast-susceptible varieties increases, the probability of an epidemic increases because more wind-borne spores pass between fields.

Correct identification of rice leaf blast is critical (Figure 1). Several diseases and disorders have similar symptoms, but control practices are not justified for these other diseases. There is a lot of diversity of lesion type so examine several different lesions at several different locations in the field. If identification is in doubt, leaf samples can be placed in a moist chamber to induce sporulation and identified by spore type (Figure 2) under a microscope.

Figure 1. Correct identification of leaf blast is critical to effective disease control.

Not Blast

 

 

 

Brown Spot

 

 

 

 

 

 

 

 

Stackburn

 

 

 

 

 

 

 

 

Chemical Damage

 

 

 

 

 

 

BLAST

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2. Blast spores.

 

 

 

 

 

 

 

 

 

 

 

If leaf blast is in the field or has been reported in the same general area, and if the variety is susceptible, fungicidal applications are advisable to protect the head from rotten neck and panicle blast.  The only fungicides that have activity against blast are the strobilurins Trifloxystrobin and Azoxystrobin.  Trifloxystrobin containing fungicides (Stratego and Gem), are slightly more effective against blast than Azoxystrobin (Quadris, Quilt, and Equation) but they are all effective. I am not sure if Gem is commercially available. Most of the time leaf blast should not be sprayed unless it is killing the rice plants. Normally a single application will control blast on a susceptible or moderately susceptible variety. The rice should be sprayed at 50-70% heading to protect the neck and panicle branches.  If a variety is very susceptible or leaf blast is still very active on susceptible varieties two applications are needed, one at 2-4 inch boot to reduce the inoculum in the field and the second to protect the head.  Remember as little as a 5 day delay in the heading application can greatly reduce control.

 

Upcoming

May 28          Southwest Rice and Soybean Field Day, Fenton. (morning)

May 28          Vermilion Parish Field Day, Lake Arthur. (afternoon)

June 16          Acadia Parish (Rice Research Station South Farm) Field Day, Crowley

July 1             Rice Research Station Field Day, Crowley.

 

Contact Information

Dustin Harrell           Rice Specialist & Research Agronomist                         (337) 250-3553    dharrell@agcenter.lsu.edu

Don Groth                 Rice Pathologist                                                                   (337) 296-6853    dgroth@agcenter.lsu.edu

Eric Webster             Rice Weed Specialist &                                                       (225) 281-9449    ewebster@agcenter.lsu.edu

Assistant Southwest Regional Director

Steve Linscombe     Senior Rice Breeder & Southwest Regional Director   (337) 296-6858    slinscombe@agcenter.lsu.edu

Mike Stout                Rice Entomologist                                                               (225) 892-2972    mstout@agcenter.lsu.edu

Mike Salassi         Rice Economist                                                                        (225) 578-2713    msalassi@agcenter.lsu.edu

 

by: Dustin Harrell

PDF version – Rice Notes 4_April 17

Rain, Rain and More Rain…

Over the past 10 days all we have seen is rain, rain and more rain.  Very little rice has been planted in Northeast Louisiana.  In Southwest Louisiana however, I would estimate that 90 to 95% of the rice has been planted and most of that rice has emerged and is moving along nicely.  In fact, when the rains first started last Friday, many producers’ fields in Southwest Louisiana had already been flushed or were in need of flushing because they were low on soil moisture.  So the rains were initially a welcome reprieve.  The problem is that the rains never let up.  Over the weekend at some locations received over 5 inches and even more throughout this week.  The rain really stopped pretty much all field work this week.   However, in many cases it has not stopped rice growth because the weather has been warm and the sun has come out from time to time.  If we look at the temperatures and rainfall at the Rice Research Station in Crowley, you will see that it rained six out of the last seven days with a total rainfall of 6.4 inches.

 

 

 

 

 

 

 

 

During that same time, it has been fairly warm with a mean daily temperature of 71.5^oF.  Often we use accumulated DD50 units to help predict rice growth and development.  DD50 heat units are an estimate of accumulated daily heat units above 50^oF and are an estimate of a day’s thermal quality for growth.  It is calculated by taking the average of the daily high and low air temperature in ^oF and subtracting 50^oF.  The short of it is that the more DD50 heat units we accumulate the faster the rice will grow and develop.  Typically, we would estimate that seedling rice will grow a new leaf somewhere between every 100 to 175 accumulated DD50 heat units.  At the Rice Research Station from last Friday (April 10) to this Thursday (April 16) we received approximately 151 DD50 heat units.  Most of my research plots moved from 2- to 3-leaf rice to 3- to 4-leaf rice this week.  All of this is to say that even though we field activities have stopped this week rice growth and development has not.  Of course, all of this DD50 discussion assumes good growing conditions for rice and not for rice which has been submerged under water.

This brings me to the most ask question I have received this week.  When seedling rice is submerged under water, how long can it survive?  Well this is a question that really does not have an exact answer and does not (as far as I know) have research based information to base the answer on.  Typically, the survival of a seedling would be related to several things including how deep the water was over the rice, variety or hybrid grown, water temperature, the “health” of the seedling prior to submergence, and so on.  So with all of these different variables in play you can see that this question would not have a one size fits all answer.  So to answer this question I polled all of the best rice farmers, consultants, and researchers I could to find the consensus was that under the current temperatures that we have and if the flood was not very deep over the top of the seedling we would feel confident that the rice could survive 5 to 7 days.  After that time, the stand would probably start to thin.

So if the rice in the area was growing this week, assuming it was not under water, we can assume that the weeds were also growing.  Which brings me to the next group of questions I was asked this week.  All of which were related to herbicide applications and wet conditions.  There are several scenarios that I was asked and so I wanted to share a few thoughts on the subject.  One is that photosynthetic inhibitors herbicides, like propanil, need good growing conditions, good weed contact, and need to be rainfast prior to the next rainfall event to work best.  So if the weeds are small, and covered with water, or you are not sure how long you will have before the next rainfall event, you may want to hold off on the application until conditions are more favorable for the herbicide activity.  After all, you are paying for the herbicide and the application costs, so you may as well get the most of what you are paying for.  Another situation, I would caution you about is applying Command treated fertilizer into a standing flood when you are expecting even more rain.  The Command treated fertilizer and the herbicide can move in the water during standing water conditions in the field when the application is followed by high winds. In this scenario, the Command can move from the high side of the field to the low end or even from the top cut of a field to the bottom cut of a field.  In these situations the Command would be concentrated (higher than the labeled rate) on one side which could damage the rice and would be diluted (lower than the labeled rate) on the other side of the field, which would provide poor residual weed control.  The same thing could occur where you apply the Command treated fertilizer into standing water, raising the flood yourself followed by wind and water movement.

 

10 Things you need to know about rice sheath blight

1. Current rice varieties range from moderately resistant to very susceptible.
2. Sheath blight is a soil-borne disease and is not transmitted by wind-borne spores. The pathogen moves up the plant and from plant to plant by surface hyphae.
3. The thicker the rice, the more severe sheath blight is.
4. The more nitrogen fertilizer used, the more severe sheath blight is.
5. The sheath blight pathogen also causes aerial blight in soybeans and attacks many other crops and weeds, making it difficult to eliminate in a field.
6. If sheath blight is detected in 30% or more of the stops in a field while scouting susceptible and very susceptible varieties, fungicide applications are advised to reduce damage. For moderately susceptible and moderately resistant varieties, the percentage increases to 50%.
7. The best timing for a sheath blight fungicide application is at the boot growth stage (2-4 inch panicle).
8. Fungicide applications to suppress sheath blight should be applied before 50%-70% heading. Application as few as five days after this growth stage will provide poor control of sheath blight. Allow time to obtain a fungicide, schedule the application, and adjust for poor weather conditions.
9. Under heavy sheath blight pressure or when growing very susceptible varieties, two applications may be needed to effectively suppress sheath blight.
10. Fungicide-resistant sheath blight pathogen populations have been found in south central Louisiana and are spreading rapidly. A sound fungicide resistance management system is needed.

 

Did you know… that according to the USDA – National Agriculture Statistics Service, the United States produced approximately 221 million hundred weight of rice in 2014?  That rice has a value of approximately 3.1 billion dollars. Well, did you know that the population of China can consume that much rice in approximately 12 days!  With that in mind, how important do you think the China market would be if we could gain access to it for U.S. grown rice?  Just a little food for thought!

Additional Information

Louisiana Rice Notes is published biweekly to provide timely information and recommendations for rice production in Louisiana. If you would like to be added to this email list, please send your request to dharrell@agcenter.lsu.edu.

This Information will also be posted to the LSU AgCenter website where additional rice information can be found. Please visit www.LSUAgCenter.com.

Upcoming 

May 28 – Southwest Rice and Soybean Field Day, Fenton.

June 17 – Acadia Parish (Rice Research Station South Farm) Field Day, Crowley.

July 1 – Rice Research Station Field Day, Crowley.

Josh Lofton, Trey Price, Boyd Padgett, Beatrix Haggard, and Steve Harrison- LSU AgCenter

As warmer and drier conditions have arrived in Louisiana, corn planting has greatly picked up.  In doing so, a lot of attention has shifted away from the winter wheat to corn.  However, while these environmental conditions greatly benefit corn planting, they also are near optimum growing conditions for the winter wheat crop.  Much of the early and on-time planted wheat around the state should have at least a couple of nodes, if not already at the boot, heading, or flowering growth stages.  Furthermore, much of the late-planted wheat has utilized these conditions to quickly progress from tillering to jointing and should also have at least a couple of visible nodes, and could be at or near boot or heading stages, especially with early maturing wheat varieties.  With this rapidly progressing wheat crop and the warming environmental conditions, increased disease incidence could be a growing issue.

Earlier in the season in juvenile wheat, many “hot spots” of stripe rust were noted throughout the state.  Even in resistant varieties, stripe rust may occur in juvenile wheat subsiding as plants mature.  In some of these “hot spots”, stripe rust progressed far enough to trigger applications of tebuconazole (Folicur and generics) or propiconazole (Tilt and generics).  Since conditions have warmed up, the ongoing stripe rust epidemic has slowed and in some cases halted.  The stripe rust epidemic may re-start if the weather pattern returns to cool and wet conditions.  Reports of leaf rust, a disease preferring warmer temperatures, at low levels have been coming in from southern Louisiana.  Leaf rust also has the potential to reach severe levels and lower yield potential.  Heavy levels of Septoria leaf blotch have been noted in early-planted wheat at the Macon Ridge Research Station.  In most years this disease does not progress far enough upwards in the wheat canopy to require fungicide applications; however, Septoria leaf blotch can be severe and limit yield in some cases.  Producers should scout fields for these and other diseases beginning at jointing.  If fungicide applications are warranted for these diseases, there are many effective products available.  Solo products or premixes containing a triazole (Group 3) are effective at slowing disease progress and preserving yield.  Applications are usually not warranted or legal after wheat has begun to flower.

Due to the excessively wet spring, many want to continue to manage N in this aging wheat crop.  However, we must take into consideration both the wheat conditions and age before continuing to manage N.  Once the wheat crop exceeds the 2 node stage, the economic return for additional N has diminished greatly.  Furthermore, once the crop has reached flag-leaf, little to no additional benefit can be gained from additional N applications.  Another aspect to consider are the crop conditions.  With the overall wet and frequent cool conditions, certain wheat field’s yield potential has decreased.  This does not mean that this year’s wheat crop cannot be productive but it does mean that additional N is probably not warranted.

For further questions or comments please contact your local extension agent or state specialist

Josh Lofton, Wheat State Specialist, jlofton@agcenter.lsu.edu

Boyd Padgett, Wheat Pathologist, bpadgett@agcenter.lsu.edu

Trey Price, Field Crop Pathologist, pprice@agcenter.lsu.edu

Josh Lofton and Steve Harrison- LSU AgCenter

Louisiana has experienced a relatively mild winter across much of the state.  This has allowed for some “catch-up” growth for a winter wheat crop that was planted in poor conditions early in the season or with better conditions very late in the fall.  However, recent colder conditions have all but stopped growth.  This is typically not an issue but with the increased over-winter growth, questions always arise as to the potential damage that cold temperatures might have on a more advanced wheat fields.  This is especially true with temperatures forecast in the lower 20’s for two consecutive nights this week.  While this  is a very reasonable question to ask, the answer is not as straight-forward and depends on growth stage, duration of cold temperatures, amount of foliage covering the growing point, soil temperature, soil moisture, and wind, among other factors.

The two most important factors  are the potential low temperatures and the duration of these cold temperatures.  Critical cold temperatures for the wheat depend on the growth stage of the crop when the cold occurs.  As can be seen from the table below (Kansas State University Extension Service), the wheat crop is least susceptible to cold temperatures during the tillering.  Wheat becomes more susceptible to cold damage as the crop progresses towards the heading stage and is  very susceptible to cold temperatures during heading.  Most of the state’s wheat crop is probably at or near jointing but some fields clearly showing one or two nodes.    During  jointing, 24°F for greater than 2 hours can cause moderate to severe negative effects on growth and yield for the current crop.  The most detrimental impact of these temperatures will be death of growing points resulting in loss of those.  This will often occur on the main stem of the tillered wheat as it is the most advanced.  Death of growing points will effectively terminate any yield that could have been expected from that tiller and may lead to development of new tillers from the base of the wheat plant.  While extensive tiller death would only occur if the crop was greatly advanced or temperatures get down to the mid-teens for an extended amount of time, which is not expected.

 

Growing points should be evaluated about a week after the hard freeze occurs.  This allows damaged tissues to start showing symptoms of discoloration and damaged stems to wilt.  Health of the growing point can be evaluated by removing the most advanced stem at the soil level  and splitting the stem.  A growing point can be identified by locating stacked plant tissue that looks similar to a beehive above the current visible nodes.  If this tissue is white, firm and fleshy, the growing point is still active and productive.  However, if the growing point is discolored and limp, the growing point is no longer active and that tiller will cease to grow and produce.

 

Determining the extent of the damage from this cold spell  and potential yield losses will be difficult until plants have time to start recovering.  Severely damaged field will put up new tillers from the soil line in about 10 – 14 days.  The damaged tillers will wilt and bleach out.  However, evaluation of the crop following the weather will give a better indication of the total damage.  There will be some superficial leaf damage and leaf discoloration in less advanced fields, but this is not likely to cause yield losses.  The hope is that the crop has adequate foliage covering the growing points, thus limiting tiller death.  For questions or concerns following these temperatures contact your local extension agent or state-specialist.

Josh Lofton- State Wheat Specialist, jlofton@agcenter.lsu.edu