Arkansas Rice Update 6-25-21

by Jarrod Hardke, Rice Extension Agronomist - June 25, 2021

Arkansas Rice Update 2021-15

June 25, 2021

Jarrod Hardke, Trent Roberts, Nick Bateman, Gus Lorenz, Ben Thrash, and Yeshi Wamishe

“Gonna buy me a ticket, to the end of the line, gonna feel the air, breathe the countryside, long as those wheels keep rolling, I’ll be satisfied, gonna ride, ride, ride.”

Summer is Here

Jarrod Hardke

It’s finally getting hot and dry and feeling like summer.  Mosquitoes are showing up with a vengeance this week and that topic seems to come up in every phone call.  Fields that don’t still have floodwaters on them are extremely dry and we need to keep up with our flood and furrow-irrigated management.  The top ends of row rice fields are drying rapidly, so if you’re not using soil moisture sensors, try to stay on top of regular irrigations.

Questions have heavily turned toward fields hitting reproductive growth.  With that, the discussions center around timing midseason nitrogen and possibly potassium deficiencies emerging.  More on those topics are covered in this update.  As a lead in, we have plenty of time to make proper midseason N applications, and we have plenty of time to correct potassium deficiencies – don’t rush to decisions that could cost you more money with less benefit.

The coming week has some chance of rainfall in the forecast for just about every day.  Who knows how much anyone will get at any point, or at all, but it looks like a very unsettled week.  Some of the earliest planted fields in the state could see heading by next weekend if temperatures hold up to drive the crop there.

Fig. 1.  NOAA 7-day Precipitation Forecast.

Midseason Nitrogen (N) Timing

Jarrod Hardke

The majority of rice acres in Arkansas currently enrolled in the DD50 Rice Management Program are entering reproductive growth.  Table 1 shows acres reaching ½” internode elongation (IE) which occurs approximately one week after the onset of reproductive growth (beginning internode elongation – BIE; green ring).

Table 1.  Percent of acres reaching ½” internode elongation (IE) by week (based on fields in DD50).

It’s important to note that our recommendations for midseason N timing have changed in recent years.  Data from 2012-2018 has shown how we can improve the timing of our midseason N applications compared to previous recommendations.

The current recommendation is to apply midseason N after beginning internode elongation AND 4 weeks after preflood N was incorporated by the flood.  You must meet both conditions before applying midseason N to maximize your benefit.

Fig. 2 shows the percent of optimum yield based on timing of midseason N after the flood was established and indicates that 4-5 weeks after preflood N is incorporated is the optimum time to apply midseason N.  Fig. 3 is another way of looking at the same data but based on days after BIE.  In Fig. 3, ½” IE corresponds with 7 days after BIE.

Again, the absolute earliest to ever apply midseason N is BIE, but only if it’s been 4 weeks since the flood was established to incorporate the preflood N.

Fig. 2.  Percent of optimum yield for midseason nitrogen (N) timing based on days after preflood N incorporated (flood establishment date).

Fig. 3.  Percent of optimum yield for midseason nitrogen (N) timing based on days after beginning internode elongation (BIE; green ring).

Identifying and Correcting Potassium Deficiency in Rice

Trent Roberts

Potassium (K), also referred to as “potash” is a plant essential element that is often limiting in Arkansas soils.  Most potassium deficiencies will be observed on lighter textured sandy loam and silt loam soils as clay soils often contain potassium concentrations well above the threshold for optimal rice growth.  Most people fail to realize that K is needed in relatively equal or slightly greater amounts in the rice plant as nitrogen (N).  Potassium is critical for water regulation in the plant, aids in several metabolic functions, and is a key component in the plant's defense system against disease.  Oftentimes, some of the first indications of K deficiency are the early onset of “nibbler” diseases such as brown spot or narrow brown leaf spot (Cercospora).  These diseases are only able to break through the plant’s natural defense system when the plant is stressed - most often due to hidden hunger or moderate to severe K deficiency.

Identifying Potassium Deficiency

Potassium deficiency is rarely diagnosed preflood and is almost always seen several weeks post-flood as the rice is growing rapidly following N applications.  Visual K deficiency symptoms in rice are expressed following the typical “mobile plant nutrient” rules of thumb:

1. The symptoms will always appear on the lower older leaves. Since K is mobile in the plant it will be moved or remobilized from the older plant growth (lower leaves) to the new growth (upper leaves).  Potassium remobilization within the plant allows the leaves that are most actively photosynthesizing to maintain as high of a level of productivity as possible.
2. Symptoms of K deficiency are expressed as yellowing or chlorosis of the leaf margins that will progress to necrosis or cell death if the deficiency is not corrected. Nitrogen is also mobile in the plant and can have similar symptoms but can be easily differentiated if you know the keys to look for.  When you have N deficiency the whole plant will tend to be yellow and stunted and the yellowing and chlorosis on the lower leaves will move down the midrib of the leaf, not the leaf margins.
3. Lower leaves will eventually die or senesce as the nutrients are moved to the upper leaves. Lower leaves can senesce when the canopy is very thick and they are no longer receiving sunlight and actively photosynthesizing, but this will often appear as whole leaf chlorosis and death rather than a pattern described for either N or K.

Tissue testing is another method of identifying or confirming K deficiency in rice.  To effectively use tissue testing to identify nutrient deficiencies the correct plant part must be sampled.  For rice that is near or past green ring, we suggest sampling the Y-leaf which is the leaf blade on the uppermost collared leaf.  Fifteen to twenty Y-leaves are required to have enough sample to complete the analysis and should be collected from the entire field or area of interest.  Recent research on using Y-leaf tissue K concentration indicates that >1.6% tissue K is optimal from green ring through mid-boot.  Our goal should be to keep the Y-leaf tissue K concentrations above 1.6% during this timeframe.

Timing of Potassium Deficiency

Potassium deficiencies are rarely diagnosed preflood due to the low demand by the plant and relatively small amount of plant biomass before N fertilizer application and irrigation.  Once rice has been fertilized with N and enters the rapid vegetative growth stage the amount of biomass increases rapidly and if there is not sufficient K in the soil to meet this growing demand we can experience either hidden hunger or visible K deficiencies. More often than not, we start to observe visible K deficiency symptoms around ½ internode elongation (sometimes following midseason N application to pureline cultivars) which can progress as the plant continues to grow and K remains limited.  Although K deficiency symptoms can occur at any time during the growing season they tend to be more pronounced and easiest to identify ~4 weeks after flooding.

Correcting Potassium Deficiency

If a K deficiency is identified 100 lb potash per acre (60 units K₂O per acre) is recommended at the first onset of symptoms and yield can be salvaged until the late-boot growth stage.  Timing of K application is critical with earlier identification of the deficiency and application of potassium to deficient rice leading to higher yield potentials.

Being proactive in the management of soil nutrients is always the best course of action.  However, it is always good to be on the lookout for potential K deficiencies near midseason as this is when they are most likely to occur and be “obvious”.  If you are concerned about K deficiency a tissue test may help identify potential hidden hunger.  Please remember that there is a wide window of opportunity for successful application of K from preplant to late-boot, but the earlier a potential K deficiency is identified the larger the return on investment.

Fig. 4.  Potassium (K) deficiency across a rice field.

Fig. 5.  Rice leaves showing potassium (K) deficiency and resulting brown spot.

Armyworm Management in Rice

Nick Bateman, Gus Lorenz, and Ben Thrash

Over the past week we have gotten multiple calls on armyworms, specifically fall armyworm, showing up in crops ranging from soybean to pastures, and of course rice.  There doesn’t seem to be a pattern on which fields these armyworms are targeting.  Our calls are ranging from 2-3 leaf rice up to joint movement.  We have done a lot of work over the past 5 years to determine when applications need to be made for armyworms in rice.

The bottom line is rice can take a lot of defoliation before we get significant yield losses.  At the 2-3 leaf stage, even with 100% defoliation, where plants were cutoff flush with the soil, we do not see a yield decline across any planting date.  We have seen a similar trend at early tiller (Table 2).

Things change once we move into late tiller and green ring growth stages.  We can get significant yield losses and heading delays if large amounts of defoliation (Fig 6-8) occur at these growth stages (Table 3).  Keep in mind that the severity of the yield loss will be worse for later planted rice.  If you notice, the May planting date has a higher percentage of yield loss than April or June.  This is related to the amount of heat units this planting received shortly after the green ring defoliation occurred.  For the June plantings, it was milder at the green ring timing allowing the rice to recover more of its yield potential.

Based on this work we have set our thresholds for defoliation in rice at:  No treatment is warranted for rice between the seedling and 2-3 tiller growth stages unless armyworms are able to feed on the growing point.  For May and June plantings, armyworms should be treated when defoliation exceeds 40% at 5-6 tiller and 20% at green ring.  During heading, treat if head clipping is occurring and armyworms are present.

If applications are needed, Lambda-cyhalothrin (Warrior II, Lambda-Cy, Silencer, ect.) is the product of choice.  Keep in mind our counterparts in surrounding states have seen a few misses with lambda due to having some corn strain fall armyworms in the field, which is resistant to lambda.  We recommend spraying lambda first and scout withing 3-4 days after application.  If there is still a large population of armyworms in the field, then we can come back with Dimilin.

Rice can handle a lot of defoliation before yield loss or delays in maturity occur.  Let’s not spray when we don’t need to, and if we do have to let’s try to go as cheap as possible.  Let us know if you need anything or need help making decision on making applications.

Table 2. Yield and days in delayed heading for different defoliation levels in April planted rice.

Table 3. Yield and maturity delays caused by defoliation at green ring.

Fig. 6.  Non-defoliated rice at green ring.

Fig. 7.  33% defoliation at green ring.

Fig. 8.  66% defoliation at green ring.

Rice Leaf Blast Alert

Yeshi Wamishe

Leaf blast has started!  We received our first report of leaf blast on June 20 on Titan in 2021 from Randolph Co.  In 2020 the first report came from the same county on the same medium grain rice, Titan.  If you have not started scouting fields planted with susceptible rice for blast, please do so.  As observed for several years, blast in Arkansas often starts in the second or the third week of June.  When you start scouting, you need to know where in the field to look for the symptoms.  Often, levees, drier field edges, high ground within a field, and field edges near trees particularly east side trees.

START SCOUTING AND RELIEVE RICE FROM RICE BLAST

Leaf blast in Arkansas starts mostly in the 2^nd or 3^rd week of June.  Frequent rain, gloomy/overcast skies are fit to the blast pathogen.  The blast fungus spores germinate when leaf wetness lasts from 9 to 14 hours.  Dew and fog in river valleys or low lying grounds often last long.  Tree shades particularly on east side of a field favor blast conditions.  Drought stress on levees, at field edges or higher grounds in shallow flooded fields serve as hot spots for spore production.  Sandier soils that do not hold flood consistently often are liable to blast.  Under any or combinations of these circumstances, a susceptible or moderately susceptible rice to blast may get sick.  Your field management particularly planting timing, seeding rates, and adequacy of nitrogen fertilization and other fertility factors play role in the severity level of the disease.  Knowledge on your field history and attempts done on variety selection to match a field helps successful blast management.

The blast fungus

It is seed-, residue- and wind-borne.  It is versatile and easily adaptable because it develops different races.  It can infect rice throughout the season causing leaf blast at early stages, collar blast at the base of leaves, panicle blast as the panicle branches push out of the boot and neck blast or node blast.

Extent of damage

Up to 100% grain yield loss depending on the parts affected.  Neck blast is the worst of all if no action is taken to rescue the crop and rescue should start early.

What to do

Scout for the disease starting late tillering if your variety has an S or MS reaction to blast (Refer to the table at 2021 Rice Management Guide page 24 to learn about your variety reaction level.

• Sometimes early detection could be difficult to diagnose as in Fig. 9 or 10 and rice seedlings may be devastated if left with no action (Fig. 11).  When you scout, look for the typical diamond shaped lesions with ashy center on lower leaves close to the ground as in Fig. 12.  Sometimes diamond-shaped lesions (Fig. 13) may coalesce as in Fig. 14.  Sometimes brown spot or drift from liberty herbicide get confused to leaf blast.
• Once the symptoms are confirmed as leaf blast, raise flood depth to at least 4 inch and keep it consistent.  This action helps to reduce spore production that may cause new infection.  Moreover, it eases drought stress on rice increasing its field tolerance.  Fungicides are not recommended to suppress leaf blast in flooded rice.  However, spot application in areas where seedlings are dying due to leaf-burn may be carried out.  If blast susceptible rice is cultivated under furrow-irrigation, not using fungicides may not be optional.

Fig. 9.  Early lesions leaf blast before sporulation.

Fig. 10.  Early lesions blast which may be confused to brown spot

Fig. 11.  Seedling death due to rice leaf blast. 

Fig. 12.  Leaf blast symptoms can easily be detected on lower leaves where dew stays longer. 

Fig. 13.  Typical lesion of leaf blast. (In memory of Jared Ford, Rice consultant in Woodruff CO.) 

Fig. 14.  Rice leaf blast coalesced lesions. 

Row Crops Radio Podcasts

Check out these podcast episodes by following the link or by listening to them on Arkansas Row Crops Radio wherever you listen to podcasts.

Insect Update and Management Strategies for Fall Armyworms and Tarnished Plant Bugs (6/24/21)

DD50 Rice Management Program is Live

The DD50 Rice Management Program is live and ready for fields to be enrolled for the 2021 season.  All log-in and producer information has been retained from the 2020 season, so if you used the program last year you can log in just as you did last year.  Log in and enroll fields here:  https://dd50.uada.edu.

Use the Arkansas Rice Advisor Internet App!

The Arkansas Rice Advisor site https://riceadvisor.uada.edu functions like an app on your mobile device.  There you can readily access the DD50 program, rice seeding rate calculator, drill calibration, fertilizer and N rate calculators, publications, and more.

Additional Information

Arkansas Rice Updates are published periodically to provide timely information and recommendations for rice production in Arkansas.  If you would like to be added to this email list, please send your request to rice@uada.edu.

This information will also be posted to the Arkansas Row Crops blog (http://www.arkansas-crops.com/) where additional information from Extension specialists can be found.

More information on rice production, including access to all publications and reports, can be found at http://www.uaex.uada.edu/rice.

Acknowledgements

We sincerely appreciate the support for this publication provided by the rice farmers of Arkansas and administered by the Arkansas Rice Research and Promotion Board.

The authors greatly appreciate the feedback and contributions of all growers, county agents, consultants, and rice industry stakeholders.