Arkansas Rice Update 7-7-23

by Jarrod Hardke, Rice Extension Agronomist - July 7, 2023

Arkansas Rice Update 2023-16

July 7, 2023

Jarrod Hardke, Trent Roberts, Camila Nicolli, Nick Bateman, and Ben Thrash

“I’m travelin’ down the road, I’m fliritin’ with disaster, I’ve got the pedal to the floor, my life is running faster.”

Heads Up

The rice is rocking and rolling of late, and now we’ve gotten the week of 4^th of July rain across much of the rice growing area.  Rice is speeding along and tracking well with the DD50 Program.

The first rice fields are beginning to head in the state scattered around.  More of the crop is getting into late reproductive where it’s time to consider late boot nitrogen on hybrids (more on that below), as well as fungicide applications.

Calls have picked up slightly for blast (Jupiter and Titan) and for sheath blight (assorted varieties and hybrids).  While sheath blight presence has been increasing, it is only just starting to take off up the canopy in some fields.  Rains this week and over the weekend may aggravate it and make it more aggressive, so be on the lookout.  There are some fields making it to heading with sheath blight still low – meaning we’ve outrun yield loss.

Overall issues appear to be calming down, fortunately.  I’m hopeful that upcoming rains won’t be impactful to flowering rice which is always a concern.  Cloudy, rainy days during flowering aren’t great, but rice tends to try and avoid those impacts.  The worst impacts are the bright sunny day when rice is in full flowering and gets hit by a pop-up storm out of nowhere – that’s usually a big problem.

Let us know if we can help.

Fig. 1.  NOAA 7-day precipitation forecast.

Fig. 2.  Early heading rice.

Sheath Blight

Camila Nicolli

Scouting for diseases like sheath blight is of utmost importance in ensuring rice health and productivity.  Sheath blight, caused by the fungus Rhizoctonia solani, affects the sheath tissue of the plant, ultimately leading to yield losses if left uncontrolled.  By actively monitoring and scouting we can implement timely and effective management strategies to mitigate the impact of sheath blight.

One of the primary reasons scouting for disease is crucial is that early detection of symptoms allows for quick action, especially for sheath blight that requires opening the canopy to check (Fig. 3).  The goal is to identify sheath blight at its initial stages before it begins to progress.  Then we can monitor progress to determine with treatment is warranted or if the disease stays below treatment level.

Fig. 3.  Scouting for sheath blight in rice.

Boot Nitrogen in Hybrid Rice

Jarrod Hardke and Trent Roberts

A few weeks ago, we covered the topic of midseason nitrogen (N) for varieties.  Now we have rice starting to approach the late boot timing (some is already there) so it’s time to talk about the late boot nitrogen application for hybrids.

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 $900/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).

Managing Rice Stink Bugs in 2023

Nick Bateman and Ben Thrash

We have received several calls this week on fields starting to head with varying levels of rice stink bugs (RSB) present.  Most fields have moderate populations with some outliers running 3-4X threshold.  It seems like a majority of RSB is still in heading barnyardgrass that are in ditches and along turnrows.  Once these grasses dry down rice will be the only game in town.  The way things are shaping up now, hopefully by the time the barnyardgrass does dry down a large percentage of our rice will be headed and will dilute the RSB populations to manageable numbers.

Since 2020 we have conducted assays on RSB to determine resistance levels to lambda-cyhalothrin (Warrior II, Lambda-Cy, etc.).  Our assays so far this year have shown between 65% and 75% control with a 1X rate of lambda, similar to assays conducted in 2022.

So, what does that mean for management of RSB this year?  Lambda still has a fit in some cases.  Keep in mind though, you cannot expect more than 50-60% control and, in many cases, late in the season it will be much lower.  If you do spray lambda our suggestion is to scout those fields within 3-4 days after application to determine the level of control achieved.  If nymphs are present when you spray and also 3-4 days after application, then that is a sign of poor control.  With that being said, if it is all adults that could mean you got reinfested.

What are our other options?  Right now, the only non-pyrethroid options available are Malathion and Tenchu.  As far as Malathion goes, it provides good knock down but essentially no residual.  We were not able to make a single application of Malathion pay for itself in our studies the past two years.  Tenchu is a good option, however it is in limited supply and can be difficult to find.  In the past we haven’t seen a big difference between Tenchu and lambda besides price.  The past three years however, it has looked much better than lambda.  Similar to Malathion, it usually takes 10-14 days to see nymphs behind Tenchu applications, and in some cases, we have gotten much longer control.

Bottom line with either of these products is we can’t afford to spray them twice.  The cost of Malathion is around $10 per acre for 32 oz and Tenchu is $11 for 8 oz.  If we are going to spend that kind of money on RSB our suggestion is to not spray until we are mainly soft dough.  That would put us on the tail end of the second week of heading into the third week of heading.  With that being said, if you are running 15+ RSB per 10 sweeps during flowering and milk you may want to consider an application.  We have done a lot of work looking at spray timing when we reevaluated our threshold, and we rarely see yield losses from RSB, but peck is extremely consistent.  If you can ride those populations through the flowering and milk stage and make one application of a product like Tenchu at soft dough, most of the time that will get us to the finish line.

We have had a lot of questions on whether Endigo ZCX will be available this season.  A Section 18 has been submitted and it sounds promising that we will receive it.  Until we have the letter in hand though it is not labeled.  We will inform everyone as soon as we hear a final word from EPA.

Let us know if you have any questions or need anything.  We will update everyone weekly with what our assays and field studies are showing.  Also please contact us if you see a failure with lambda so we can make a collection to conduct resistance assays.

Fig. 4.  Rice stink bug control 7 days after treatment (DAT) for trials averaged across 2021-2022.

DD50 Rice Management Program is Live

The DD50 Rice Management Program is live and ready for fields to be enrolled for the 2023 season.  All log-in and producer information has been retained from the 2022 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.