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Delta Farm Press
by Jarrod Hardke, Rice Extension Agronomist - July 7, 2023
“I’m travelin’ down the road, I’m fliritin’ with disaster, I’ve got the pedal to the
floor, my life is running faster.”
The rice is rocking and rolling of late, and now we’ve gotten the week of 4th 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.
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.
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.
Preflood N only
PFN + 30 lb N @ midseason
PFN + 30 lb N @ late boot
PFN + 46 lb N @ midseason
PFN + 46 lb N @ late boot
PFN + 30 lb N @ midseason & 30 lb N @ late boot
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).
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
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
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
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.
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.
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 firstname.lastname@example.org.
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.
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.
Rice Extension Agronomist
Extension Weed Scientist
Rice Verification Coordinator
Extension Rice Pathologist
Extension Soil Fertility