Arkansas Rice: Crop 50% Heading; Conditions Ripe for Disease Development

Rice flowering in early morning dew. Photo: University of Arkansas

Crop Progress

“It never rains in Southern California.”  That song came on just as we were getting some of the first measurable rainfall in weeks.  Just wait a while and the weather will change.  That’s traditionally been true of Arkansas weather, and hopefully the forecast is correct and that happens again next week.

The majority of rice in the state has reached the 50% heading stage.  Flowering is getting into full swing and we need good conditions to set us up for solid yields.  High temperatures both day and night have been a concern recently, but there’s relief in sight.

Starting this weekend we’re forecast to have temperatures fall into a reasonable range.  If this holds true, we’re going to be in much better shape.  Maybe one thing will go right.

The first rice in the state is expected to reach harvest moisture the first week of August.  That’s the forecast time for 20% grain moisture on those fields.  Even with temperatures supposed to level off a little, we should still remain on that track.  If the dry conditions largely continue, we need to be careful about draining the first rice too early, as the soil may dry much faster and risk yield loss.

Continued heavy dew, fog, and light pop-up showers aren’t our friends right now.  These conditions can impact flowering and possibly yield.  In addition, these are prime conditions for disease development (more detail on disease later).  Finding blast infections of leaves and leaf collars is not a good sign at the moment.

In fields that are blast-prone – difficult to maintain adequate flood, near tree lines, susceptible cultivar – it’s important to be proactive in blast management.  Under current conditions blast infection is more likely and we should be careful in problem fields.  This is not to say that every field out there needs to be treated, but side with caution when deciding whether to spray or not.

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Fig. 1. Extended forecast for North AR, July 20-29.  Click Image to Enlarge

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Fig. 2. Rice flowering in the early morning dew.

Insect Update

Rice stink bugs (RSB) continue to show up in fields at relatively low levels.  We seem to have enough rice heading at one time to keep our typical early problem fields from showing up.  Wait until 75% heading in a field before making treatment decisions.  This allows RSB in the field to spread over the field and give us a better idea of the actual density.  If the numbers are over threshold after that point, it’s time to treat.

Rice Field Day Scheduled for Friday, August 3rd

The Rice Field Day at the UofA Division of Agriculture Rice Research & Extension Center is scheduled for Friday, August 3, 2018.  Full details can be found here.

Disease Update

Blast

No new counties reported blast in rice this week.  Until last week blast was reported in 15 counties.  However, this week, more fields planted with Diamond were reported with leaf blast and a few on collar blast.  Collar is the junction between a leaf sheath and leaf.  Collar blast extends both to the leaf and sheath but is more to drying out leaf blade faster than the sheath.  Collar blast on flag leaf can be a source for neck and panicle blast.

Therefore, applying timely protective fungicides is largely to protect flag leaf collars from blast (Fig. 3), panicle necks from neck blast or neck rot (Fig. 3) and the panicle branches from panicle blast (Fig. 3).

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Fig. 3. Collar, leaf, and sheath blast infection as well as neck blast (left); panicle blast and neck blast (right).

Three important points to remember:

  1. Fungicides are more beneficial in well managed fields;
  2. Maintaining flood depth to at least 4 inches has more power to suppress blast than the fungicides;
  3. adequate water volume (at least 5 gallons/acre) for fungicide application is very important to obtain the desired results.

Note that no reports from some counties on blast does not necessarily mean there is no blast.  Keep scouting.  Timing is important, if fungicide protection is required.  To read more on blast go to Scouting Blast Disease.

Sheath Blight

Weather is warm, humid with erratic rain showers – perfect for sheath blight disease development and progress.  In our artificially inoculated plots both at Stuttgart and Pine Tree, sheath blight has progressed very fast within a few days.  Please scout your fields.  The disease progresses vertically up rice plants and horizontally to neighboring rice plants.

Fungicide applications are recommended between panicle differentiation and boot split at threshold levels for susceptible and moderately susceptible rice.  If the rice is past these stages but sheath blight is threatening the upper two or three leaves including flag leaves, fungicide application may be considered up until 50% heading so that grain filling may not be affected in addition to the concern for crop lodging.

Remember to check for the pre-harvest interval on the label before application.  Labels are the rules.  To read more on sheath blight scouting, threshold levels and more go to Arkansas Crop Scouting.

Kernel Smut and False Smut

Warm, humid, and wet weather conditions are favorable for kernel smut.  False smut is more favored by wet and lower temperature than needed by kernel smut.  A field with history, planted with a susceptible cultivar, seeded thick and receiving excessive preflood nitrogen fertilization are prone to either or both types of the smuts.  To read more on common questions go to Common Questions and to read more on management of these smuts go to Common Mistakes on Fungicides.

Bacterial Panicle Blight (BPB)

Although we received a few samples of rice this week with discolored panicles, none of them were identified as BPB.  There is no report of BPB so far in 2018 from commercial fields.  However, the extended high nighttime temperatures may enhance BPB development particularly coupled with some level of moisture in the form of dew, fog, mist, or rain.  The bacteria can also be blown around from infected rice to neighboring rice by windy rain.

But the extent of spread is not as extensive as in blast pathogen spores.  We can do nothing after BPB is visually detected in the field.  But the information would be useful to know the quality of our seed sources for the following planting season.  The disease is mainly seedborne.

The earliest developmental stage to visually detect BPB in the field is at early grain fill (Fig. 4) after flowering.  For symptom identification go to BPB Identification.  To read more on BPB go to Bacterial Panicle Blight and Beyond and BPB Research Update.

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Fig. 4. Panicles with bacterial panicle blight are discolored an remain erect compared to healthy panicles that tip down.

New DD50 Program is Live!

Check out http://DD50.uaex.edu for the overhauled DD50 Rice Management Program.  We have tried to make this version extremely user friendly, but in doing so it is a little different than the old version.  If you run into any issue, please call or text me directly at 501-772-1714 or send emails to riceadvisor@uaex.edu.  It also works great on mobile phones and tablets.


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