Arkansas Rice Update 6-21-24

by Jarrod Hardke, Rice Extension Agronomist - June 21, 2024

Arkansas Rice Update 2024-12

June 21, 2024

Jarrod Hardke, Camila Nicolli, and Trent Roberts

“On a long, hot summer day.”

Rice is Rolling, Temps are Roasting

Half of my rice looks great, the other half I don’t want to talk about.  Seems to be the most common phrase uttered this week.  In reality most of the crop looks very good.

Our weed control efforts looked way better a couple weeks ago but now we’re starting to see more grass popping out of the canopy and telling us we didn’t quite clean it up like we thought.  These won’t be yield-limiting populations (in most cases) just an eyesore and aggravation.  Gentle reminder that most rice is past midseason meaning you have no herbicide options and even if you did have them the weeds are too big to kill anyway.

The name of the game is keeping adequate water to the rice through these increasing temperatures (both day and night).  Most seem to be in very good shape at this point having gotten well ahead under the milder conditions of previous weeks.  It’s easier to stay caught up than it is to catch up when it comes to rice irrigation.

This coming week we’ll start to see the first rice in the state heading, which means we’ll have a lot of rice potentially ready for harvest in the first half of August this year.  A lot of time and weather between now and then to move that around, but for the most part you better get your harvest equipment ready early this year.

Let us know if we can help.

Fig. 1.  NOAA 7-day precipitation forecast.

Boot Nitrogen in Hybrid Rice

Jarrod Hardke and Trent Roberts

For hybrid rice – we recommend a preflood N application dependent on soil texture (generally 120 lb N/acre on loam soils and 150 lb N/acre on clay soils) followed by a late boot application of 30 lb N/acre.

What is the late boot timing?  Once the flag leaves on main stem tillers are fully emerged to where you can see the leaf collar up until boot-split.  This is the late boot stage.

What is the recommended rate?  30 lb N/acre (65 lb urea/acre).  Rates higher than this have not displayed an added benefit.  There’s no reason to apply 100 lb urea/acre “just because you’re paying for 100 lb minimum flying”.  That just means you’re adding another cost of 35 lb urea that isn’t giving a benefit.

Why the late boot and not a midseason application?  The preflood N rate for hybrids is sufficient to supply season-long N needs for hybrids.  Any potential shortfalls during the season can be resolved by the hybrids taking up additional native soil N to bridge the gap.  So, a true midseason is not needed to drive overall yield potential.

The late boot N application to hybrids serves to reduce lodging potential, slightly improve yields, and slightly improve milling yields.  If you were to make this application earlier at a true midseason timing (e.g. around ½-inch internode elongation), we would still expect similar benefits, but some negative consequences could occur such as increased plant height and increase rank (excessive) growth.  Stick with the late boot timing to get the positives while minimizing the negatives.

Table 1.  Data from a single 2022 trial at Stuttgart evaluating timing and rate of midseason and late boot nitrogen (N) applications to hybrid rice (RT XP753) – net return was calculated using $6.50/bu rice as a base adjusted for milling yield minus a generalized operating cost base of $1000/ac with costs for N added based on treatment.

What about other N sources?  The late boot N recommendation is to be applied as urea.  After rice enters reproductive growth, it can take up urea N with high efficiency (90% uptake) when grown under a continuous flood.  Foliar N applications cannot supply these N rate levels.  A foliar N product containing 32% N can only deliver 3.2 lb N per gallon.  Even if applied at 3 gallons per acre and similar efficiency to urea, you’re only getting 8.6 lb N versus 27 lb N from urea (at 90% uptake for each).

Hydrogen Sulfide Toxicity

Jarrod Hardke

Based on a few questions this week – note that hydrogen sulfide toxicity is a completely different disorder from delayed phytotoxicity syndrome (DPS).  They aren’t related.

Unfortunately, we seem to have made our way into a year with increased hydrogen sulfide toxicity.  Given that we have spent much of the past 6 weeks or so with wet to saturated soil conditions off and on, perhaps it shouldn’t be that great a surprise.

It is always wise, anytime we see any disorder, to look over the entire plant to best determine what’s going on.  In some cases where similar leaf effects have been observed but occur more frequently among all leaves on the plant, is a nutrient draw related to hydrogen sulfide toxicity (Fig. 2).  A quick look at the roots can clearly show if there is a significant amount of blackening related to hydrogen sulfide toxicity.

Hydrogen sulfide is toxic to cells and when present in the soil can lead to root cell death and the blackening that occurs.  The reaction that generates hydrogen sulfide gas occurs in anaerobic soils and when it kills the roots prevents them from delivering needed nutrients to the plant.  When this issue occurs during reproductive growth stages, it is much more difficult to safely and effectively overcome.  To truly eliminate the problem, draining of the soil is required to return oxygen or aerate the soil and reverse the reaction.  However, in reproductive stages there is a risk of a severe drain reducing yields, so instead the attempt is to reduce the flood to a muddy / firm state to get some oxygen to the roots and then reflood.  This often allows us to outrun the issue and maintain yields, but it is still very difficult during the hot and dry period of summer.

Attempts have been made over the years to identify cultivar differences in susceptibility to hydrogen sulfide toxicity (Table 2, Figs. 3 and 4).  There do appear to be some differences among cultivars which would make sense given differences in the physiology of root masses of different germplasm.  However, if you look closely through the data you’ll see a great deal of variability that suggests it may be difficult to dependably select cultivars.  It is worth noting that most of the cultivars in these trials that showed some of the worst hydrogen sulfide issues are no longer grown.

Fig. 2.  Hydrogen sulfide toxicity.

Table 2.  Rice cultivars evaluated for tolerance or resistance in a problem field for autumn decline in Hunter, AR in 2016.

Fig. 3.  Percentage root mass discolored, plants with crown rot and extent of crown rot as estimated in 0-9 scale in a field test using pots filed with soil with a history of hydrogen sulfide toxicity and autumn decline.

Fig. 4.  Ranking in rice cultivar response to hydrogen sulfide toxicity and autumn decline using index from combined ratings of percentage root mass discoloration, root crown rot and frequencies.  The first 14 cultivars did not show any level of crown discoloration.

Rice Disease Update

Camila Nicolli and Jarrod Hardke

Leaf blast reports continue to roll in with warm but mild temps, high humidity, and windy rain events.  We want to stress that we do not recommend treating for leaf blast unless it is starting to burn down areas of the field – this is typically rare, but this year may be unique.

Rather, we prefer to see flood depth increased to suppress blast development.  If in a row rice situation, try to minimize drought stress as much as possible, which will encourage blast infection.  Back water up from the bottom as much as possible to have more of the field flooded but avoid excessive depths on the lowest rice that will stretch it out.

Over the past week, we have observed the presence of some leaf blast in hybrid rice in a couple fields (so far in RT 7521 FP).  Upon checking the lesions, we found that the spores are active and producing secondary spores.  We are looking into this issue and don’t want to cause any alarm – but we do want you to let us know if you find any blast-type lesions (diamond-shaped, grey center with brown margin) in any hybrid rice fields so we can monitor the situation and collect samples.

Fig. 5.  Leaf blast in a field of RT 7521 FP in northeast Arkansas.

CBOT September Rice Futures, 10-Year Monthly Continuation.

DD50 Rice Management Program is Live

The DD50 Rice Management Program is live and ready for fields to be enrolled for the 2024 season.  All log-in and producer information has been retained from the 2023 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.