Rice and Advice: Episode 05 
Title:  Rice Fungicide Timing & Decision-Making 
J. Hardke 7-29-21

Welcome to Arkansas Row Crops Radio. I’m Jarrod Hardke, rice extension agronomist with the University of Arkansas System Division of Agriculture. 

Today on Rice and Advice let’s talk a little bit about fungicide timing. A lot of rice in the state, certainly we’re getting, moving into heading or already have been on some of the earliest rice. A larger portion of the crop is just getting close to heading or just trying to start. We’re a little bit delayed. It seemed like some of the earlier season weather kind of set the crop off by a handful, five to seven days, even potentially with what happened with the cool spell if you remember back around Memorial Day, so maybe tracking just slightly behind what you would expect or anticipate at this point, but we’re still doing pretty well on track. But really not to waste any time, to kind of dive in, certainly one of the earliest questions coming in or has been coming in around has to do with fungicide applications to prevent kernel or false smut or just the smuts in general. And really what we’re after there, taking kind of a check list approach. 

The first most important thing, do you have a field history of kernel or false smut? And in some instances you may or may not. There was certainly a period back around 2015 where we had a great deal of sooty mold on the outside of a lot of our rice. It wasn’t actually kernel smut that was inside the kernel but sooty mold that’s opportunistic fungi form on the outside, so we had some black combines from that. I know some guys probably been spraying for the smut just about ever since, you know just from that problem and really it may not be needed. Additionally there have been a couple of years on the way here where if we planted some very susceptible cultivars to false smut and had a little bit of that, it’s extremely showy, typically not to levels that are truly detrimental and because of the way it forms and the way it can be removed in the milling process and dry down process it’s not as detrimental, at least at this point as cornel smut can be. 
So the first thing do you actually have a field history? That’s the first check box. Next thing certainly have you planted a susceptible cultivar? Certainly we’re really worried about the VS or very susceptible cultivars and then somewhat the true S susceptible anything that’s probably ms and that’s about as high as we rate anything against the smut’s around ms, it’s not that likely that we’re going to need an application. 

Another check box, later planting dates, mid May and beyond typically are going to have a tendency to be more prone to having the smuts. And then using excessive nitrogen rates, so if we’re pushing nitrogen rates really trying to push yield over the top those excess nitrogen rates or if we feel like we’ve had to add to it given the year to try to push the crop along and make sure we have adequate amounts we may be over fertilized. So really the more of those four factors that you can check the more beneficial a fungicide application may be. That field history, susceptible cultivar, late planting date and excessive nitrogen end rate. So really we’re going, if we do check a lot of those boxes, we want to apply a minimum of six ounces per acre of Tilt or the equivalent so that could be an application of Quilt Xcel, could be Amistar Top , which has a different, Hemastar Top has a different triazole in it so we want to be in the higher range of it. Fourteen ounces say for instance to try to get that rate up, but anyway that equivalent to six ounces per acre of Tilt is usually going to get the job done. The more severe history potentially some even higher rates could be used. The timing is from mid-boot all the way into the early part of late-boot, so as a visual in the field, when the flag leaf starts to be on its way out, it’s still pointing straight up, the flag leaf still mostly in the boot starting to work its way out, that’s an easy visual for a good start of that window and then once you’re into late-boot, that’s when the flag leaf’s all the way out and you can see the collar on it. Once you’re just into late-boot maybe by a few days, by then we need to have the application out. When we get too close to the end of late-boot, boot-split for instance, to beginning heading, we don’t have enough time to move that fungicide in the plant where it needs to go, so the goal with getting it out there early is to allow that fungicide to move systemically into the plant where we need it to give us the protection, so that’s kind of the window of application and what we’re after trying to time and control the smuts in this instance. There’s always a lot of questions about should I throw in an insecticide with the Tilt application or something else this kind of timing just prior to heading? The answer’s no. Research done by Nick Bateman, Gus Lorenz has shown that that can have a tendency to flare rice stink bugs later. They’re typically not there in the field. If they are they’re on grasses, we’re going to knock out all the beneficial insects in that case and possibly increase the odds that we’re going to have to spray again.

The other question usually more directed at hybrid cultivars is what about putting in some kind of liquid nitrogen product to go along with the fungicide application, that way I can do away with that late-boot urea shot, then I don’t have that extra trip and that urea cost. And we’ve written on this some in updates but at the end of the day there’s just not enough nitrogen that we can get out in that foliar application to compete with the thirty pounds or thirty units of nitrogen we’re getting out of that late-boot urea application of sixty-five pounds to the acre, but we just can’t get there. Even if you take a very large percentage nitrogen product like UAN that’s thirty-two percent, it’s going to be a ten pound per gallon products. If you’re running a gallon of it you’re still only getting 3.2 pounds. It’s not going to be taken up with any more efficiency, our late-boot, any type of mid-season or late-boot timing application of urea is going to be taken up with extremely high efficiency. So a pound is a pound, we’re getting thirty pounds out there with urea. We’re not going to be able to get anywhere near that with a foliar application and then if you try to get anywhere close by really running those foliar end products up at much higher rates, then you’re going to be putting out largely straight liquid in and you bring into play a lot of burn to those upper canopy leaves, the flag leaf and if any heads have begun to pop at all you’re going to burn and ? them too so you generally want to try to avoid that as well. 

Shifting gears just a little bit to talk about sheath blight. Recent weather does seem to have sheath blight on the move. We’ve been pretty hot, very high humidity, pop-up showers. That disease is on the move, we go back to kind of the check list approach. Susceptibility of the cultivar. Percent positive stalks for sheath blight. The health of the upper three leafs in the canopy. And then excessive nitrogen rate or seeding rate and or seeding rate. So certainly susceptibility of the cultivar. That’s something we have ratings where you can look at. The percent positive stops is based on the susceptibility of the cultivar, so you’re looking at the threshold is thirty-five percent positive stops for sheath blight when you have a very susceptible or susceptible rated cultivar. Fifty percent positive stops when you have a moderately susceptible rated cultivar. One key difference though in keeping these check boxes in mind is that just because you hit that threshold for percent stops just because you can find sheath blight down there very low on the canopy at the water line does not necessarily mean that there is economic value to a fungicide application at that time to go after sheath blight. We’re worried about protecting those upper three leaves in the canopy in trying to get to get to fifty percent heading with the upper three canopy leaves clean. So when you get to fifty percent heading, you’ve got the flag leaf, flag leaf minus one and flag leaf minus two. If you make it to fifty percent heading and those three leaves are clean, then you’ve outrun yield loss. Now there are other reasons to consider making a sheath blight application. If it looks like it’s pretty aggressive, even fairly late around that time and that it may blow out the top late, you may not have direct yield loss but we could be worried about increase lodging potential because we do have a lot of sheath blight and it does look like it’s going to go out and take some of the rice down, maybe a low rate application could have some value to protect us in the long run. But again our goal is to outrun it and just avoid that application at all. If we’re just talking about Quadris as an example or any equivalent containing similar strobilurin, if you’re applying Quadris , twelve ounces is going to give you twenty-eight days of suppression, ten ounces will give you about twenty-one days of suppression or eight ounces will give you about fourteen days of suppression, against sheath blight. 

One last thing to touch on. We’re not growing very many blast susceptible cultivars at this point and time. There aren’t many out there. But we do still have some and so it’s worth repeating again trying to prevent neck blast and panicle blast. Go back to those check boxes. Do you have a field history of blast, you’re on a susceptible cultivar, a late planting date, May and later. That’d be half the crop this year. And then low water availability or irrigation capacity. Again back to the more boxes you can check the more beneficial a fungicide application could be. And in this case there’s a couple of different directions to go if you’re dealing a truly susceptible cultivar and have concerns, then it’s two application approach of again a Quadris type product, an azoxystrobin, at this point where the first application needs to be targeted late-boot to ten percent heading and a follow up application of a similar rate, ten to twelve ounce rate around fifty to seventy percent of the head out. Neck still in the boot but fifty percent to seventy percent of the length of the head is already out. But again neck still in the boot, that’d be the two application approach really needed for those most severe situations where we feel like we’re most at risk. 

For our other cultivars that maybe have minimal susceptibility or the situation’s otherwise great, it’s planted earlier, not really any history, irrigation’s pretty good, were going to take a conservative approach and make an application if you want to do that and try a single fungicide application approach, you’ll be trying to basically split the difference between the two shot approach, so around there roughly when thirty to fifty percent of the head or the primary tillers are out of the boot but the necks are still in the boot, make that one application and again ten to twelve ounces Quadris or equivalent is going to kind of get us to where we need to be. 

So that’s kind of a really brief rundown on our fungicide timings for three of our major diseases out there. Again just kind of going back to that check box approach and kind of what we can do to make it a little simpler kind of that additive, the more boxes you check, more likely you’re going to get a benefit out of that fungicide application. So we certainly hope we have a good finish to the season. It’s pretty hot out there at this point and time and so irrigation in keeping flood levels up is a concern and otherwise management concern there is a lot going on in the insect world to get into as well but we’ll leave that to the bug guys.

So if you have any questions feel free to reach out to myself or Dr. Yeshi Wamishe, extension plant pathologist, to discuss more about fungicide options or timings. Exactly what we’re after there. Hopefully this has been a nice little overview that you can use on the farm, so thanks once again for joining us on this episode of Rice and Advice on Arkansas Row Crops Radio. Have a rice day!