Episode 14 - Rice Growth Stages & Fungicide Timing

Arkansas Row Crops Radio, providing up to date information and timely recommendations on row crop production in Arkansas.

Jarrod Hardke: Welcome to Arkansas Row Crops Radio. My name is Jarrod Hardke, Rice Extension Agronomist for the University of Arkansas System Division of Agriculture.

Today let's talk a little bit about rice growth stages and how that relates to fungicide timing. So, a few things to think about to kind of generalize the growth stages of rice and what we're gonna focus on today will be the reproductive growth stages. So, really starting with what we refer to as Beginning Internodal Elongation (BIE) or green ring and so from here, you can very generally think across all of our available cultivars whether they're varieties or hybrids, roughly 28 days from green ring to 50% heading, beginning heading we start to see those panicles emerge out of the plant, out of the boot. So, it can be slightly shorter to a little bit longer so you know, a range of 26 to 30 or maybe even sometimes 26 to 32 days for this whole window to take place but if you think about it taking right at 28 days, 4 weeks its a nice round number to picture in your head to illustrate. So, if you think about green ring being day 0, the very beginning of reproductive growth then at roughly day 7 you have half inch internodal elongation which is obviously one of our key timings of growth when we talk about mid-season nitrogen and some other things, one we're always looking for and that's the first time you can get a really good look at the beginning of the panicle at that stage but in reality when it seems extremely early for how most of us have traditionally talked about the reproductive growth stages. Half inch internodal elongation would truly be the very very beginning of early boot at that point. I know, seems very early but keep that in mind, that is the beginning of the panicle forming and starting to move up the plant. So, that's at day 7, at about day 14, roughly is when we should actually be at around mid-boot and that's a timing when you should be roughly seeing what will be the flag leaf beginning to point. Well call that point leaf still sticking straight up still working its way out at that point, still has a little time to go to get fully out but that's the beginning of mid-boot at that timing when the flag leaf itself is beginning to work itself out of the plant, you can visually see it. It's hard to always know that that is the flag leaf on the way out, that's where things like the DD50 program come in handy to give you an idea about how far out you are from heading. But, so, day 14 kind of starts mid-boot at that point in time and then when you get to roughly day 21 after green ring that's late boot and that's easily defined as when the flag leaf is all the way out and you can actually see the leaf collar on it and the quick double-check there is there will be no additional leaf coming out of the plant. You know that's it, that's the flag leaf. And then you're only about seven days away from heading at that point. And so, what we want to focus on and think about when we're talking about fungicide applications across these growth stages. Is that let's focus on is smuts for a moment, kernel smut and false smut is oftentimes what people are misidentifying is as late boot is actually immediately proud heading, which is really too light to get much benefit out of a fungicide application for smut prevention. So, what we're actually shooting for is it truly that that beginning of mid boot, that 14 days. So, 14 days after green ring, 14 days prior to heading, that's kind of the beginning of the optimal window there, that mid boot window from 14 to 21 days after green ring. So, again, one to two weeks prior to heading, that's our optimum window. Once we fully get into late boot or hit late boot, we can still get good smut suppression from our fungicides, the triazoles. But every day, closer to boot, split and heading, the less suppression we're going to get those smuts. The triazoles are systemic but they need time to move and get into those plant parts to protect and prevent smut development from kernel smut and false smut in the plant. So, again, we've got to give them time if we're spraying them way too close to heading them. We're not getting much benefit out of those applications. 

If we shift gears just a little bit and talk about sheath blight, we don't even want to start scouting really for sheath blight until around half-inch Internodal Elongation. Again, seven days that seven day after green ring number. And then, we're really going to act based on scouting. So, when we're looking, we really know what the cultivar is, is if it falls in the susceptible to very susceptible category, then we then we're looking to find a minimum of 35 percent positive stops in the field, half sheath blight present. But if it's a moderately susceptible M.S. cultivar, then then it really needs to have 50 percent or more positive stops in the field. But keep in mind that that's a percentage of stops where you found the disease. But that doesn't mean that just because you get that, that you need to trigger a fungicide application. We need to find that many stops and have the disease moving upward in the canopy, threatening the upper leaves. If that's not happening and it's just present in the field, then we can potentially outrun it. If we can make it to 50 percent heading and have the upper three leaves of the canopy be clean and not have sheath blight on them then we have outrun the yield most potential. And we've saved time and money by not making those spray applications. Now, one thing that we do encounter sometimes as we approach get right at 50 percent heading questions about it's moving up. Maybe it's not really necessarily going to be yield threatening, but there is a lot of sheath blight present in the field and there can be some concerns over stock integrity in that sheath blight by weakening the stands. And so, will it hold up very well through the harvest window. And so, in some cases, it could be advisable to make a low rate fungicide application to suppress it for a shorter period of time for that stock integrity. But that's something that has to be looked at pretty closely and will generally be a rare situation that we need to do that just since we're on the topic. We'll go and throw in a few comments on blast prevention as well, certainly primarily focused on varieties. If you do have a situation where you feel like you need to make blast preventative fungicide applications, the first application is really desired to go out in that late boot window. Once flyleaf collars are exposed, the flag leaf is all the way out to the very beginning, heading for the first application and then well into heading pentacles about halfway up. But all the neck still inside the boot when the second application goes out. Generally speaking, maybe about a week later after the first one, in a lot of situations, folks are probably only going to target a single fungicide application. And that probably needs to lean toward just a little after heading begins. Again, we're trying to kind of then split the difference with a single application leaning toward a higher rate on that one and try to protect as much as we can, but save money on the total application, begin that. That's going to be an individual decision based on cultivar susceptibility, field conditions, prevalence of blast disease around that at the time of heading in. We can't go backward on blast. We either spray forward and prevent it or we don't, particularly when it comes to neck blast. So those are just a quick rundown on growth stages and some fungicide timing issues to keep in mind. Again, working through those better to be on the early side, particularly for the smuts rather than late that if we're going to get the most we can out of it. Don't pull the trigger too quick, though, on sheath blight applications. We want to try to outrun it, if at all possible, back up from there. But then right back around on the blast, we've got to work in front of it. If we're going to prevent neck blast and panicle blast from being an issue. 

So hopefully that's answered some questions about growth stages in rice as far as reproductive growth and fungicide timing. If you have any questions, please let us know. Reach out to your local county agent. We'll all be happy to help as much as we can. Thanks for joining us again on Arkansas Row Crops Radio.

Arkansas Row Crops Radio is a production of the University of Arkansas System Division of Agriculture. For more information please contact your local county extension agent or visit uaex.edu