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Intro: This is a GRDC podcast.

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Shannon Beattie: Rhizoctonia root rot is an important disease of cereals in the southern and western growing regions, especially in low rainfall areas. Losses have been estimated at about $15 per hectare for wheat and $12 per hectare for barley in the southern region. Hi, I'm Shannon Beattie. Fungicide control of rhizoctonia has proven to be difficult, often with mixed results with seed treatments. In this episode, I'm joined by Blake Gontar from the South Australian Research and Development Institute to talk about a previous GRDC investment that showed streaming fungicide above and below the seed was an effective way to protect cereals from rhizoctonia and get the greatest yield responses.

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Blake Gontar: It's a soil borne fungus, and it persists in the organic matter in the soil. It causes a disease in mainly cereal crops but can also impact pulses and to a lesser degree, canola.

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Shannon Beattie: And are there particular areas that tend to be affected by rhizoctonia more so than others, particular growing conditions or anything like that?

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Blake Gontar: Yeah. So rhizo has a really niche requirement. It is best suited to sandy soils, kind of drier, tougher environments. It thrives in low rainfall environments, although it will persist in higher rainfall. And it particularly likes cold soil conditions.

00:01:38:09 - 00:01:50:11

Shannon Beattie: So cold and dry or drier, lower rainfall areas. Can you give us a bit of an idea of where around the country we are more likely to see rhizoctonia in, I guess, more severe instances.

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Blake Gontar: So because of those conditions, it's really common right the way around from Western Australia through to southern New South Wales. So they're the areas where we have winter dominant rainfall and sandier soils. As soon as you move into summer dominant rainfall, we have warm, wet conditions, rhizoctonia doesn't thrive. So in that southern and western GRDC region, sandy soils, cold, wet winters and especially when we get a drier winter are really favourable.

00:02:26:07 - 00:02:35:24

Shannon Beattie: And I understand that there are different varieties that can have a different severity of disease within them. Can you talk to me about that?

00:02:36:03 - 00:03:07:04

Blake Gontar: The biggest differences are between the crop types. In general, canola is not badly affected by rhizoctonia. Pulses a little less so than cereals. It's mainly the cereals that are impacted within the cereals; there's not a lot of variation in tolerance or resistance. There's some anecdotal evidence for crops that do better with rhizoctonia, but none of them are truly resistant and no varieties are truly resistant.

00:03:07:22 - 00:03:25:15

Shannon Beattie: Are you able to talk to me about the factors, obviously we said dry conditions and it being colder, but I believe there's also a difference between the base level infection and the crown rot, the root infection. Can you talk to me about that and what contributes to those different factors?

00:03:25:22 - 00:04:40:03

Blake Gontar: Historically, rhizoctonia was seen as a seedling disease, and that's because with early infection, it attacks the seminal roots. So the primary root system is attacked and we get stunting in the plant with that early infection. As we've moved into a seeding system that sows earlier, we tend to be sowing into warm, moist soils that are not favorable to rhizoctonia. So we actually don't get as much seedling infection, as much infection of that seminal root system. So often we avoid the bare patch symptom, the real stunting symptom. But what we do get as soil temperatures cool, we get infection of the crown roots. So these are the secondary root systems that develop into that surface layer. So whilst we might get an established plant looking pretty good, we're then going to get almost a subclinical infection. So an infection that's not highly visible but which, if it's occurring in a well-established high yield potential crop, it actually has the potential to reduce quite a bit of yield in that crop without us necessarily knowing it.

00:04:40:13 - 00:04:54:22

Shannon Beattie: When it comes to these different types of infection, how do we notice them in a crop itself? What are we looking for in a crop to see, oh okay, I think I might have some right here in here.

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Blake Gontar: Yeah, so as I said, historically, we have been looking just for big bare patches in that crop, and that would have been a really big indicator that rhizoctonia is there. So patches that are, say a couple of metres wide through to 10 or 20m wide would indicate a rhizoctonia problem. We don't tend to see that quite as often now, unless we get a late sowing or particularly tough soil that we're farming on. But what we're more likely to see is around about late tillering to early stem elongation stage, we'll start to see some general waviness in the crop. The crop will just look a bit raggedy, not tabletop even. And that's an indicator that we've got rhizoctonia in that secondary root system. And it's having an impact on tiller development and maybe just reducing a bit of growth generally in some plants.

00:05:54:06 - 00:06:06:18

Shannon Beattie: I understand that fungicide rhizo has proven to be a little difficult at times. Why is that? Why do fungicides not seem to work properly or difficult to implement?

00:06:06:20 - 00:07:42:12

Blake Gontar: The issue with fungicides, particularly with seed fungicides, is that whilst there's no doubt that they do work, they are effective under certain circumstances. They're applied very early on and often by the time we actually get rhizoctonia infection two months down the line, that seed treatment has dissipated. So we're actually applying it early and sowing early when the problem isn't there. And then by the time the problem ramps up in June or July, that seed treatment has moved away. Lost efficacy. The second issue with a seed treatment, of course, is there's really only so much fungicide we can pack onto a little seed for each and every seed. So part of it is just around the distribution, the amount of fungicide we can get. The third issue with a seed treatment is naturally, when we put a seed down, we get water or rainfall moving that seed treatment down the profile. So we're going to get protection of that seminal root system. But as I said earlier, that often isn't necessary in a modern farming system because those seminal roots develop before rhizoctonia is even an issue. The problem then is that the surface roots, the secondary root system, the crown roots which emerge, they actually emerge above the seed treatment. So they're completely unprotected by seed treatment. And the rhizoctonia takes advantage of that.

00:07:42:22 - 00:07:58:12

Shannon Beattie: What are our alternative options then? There's a term that's been thrown around in the brief for this podcast. But I'm not going to lie, I have never heard before. Which is surprising because I've been in this industry for a pretty long time now. And that is liquid streaming application.

00:07:58:14 - 00:09:31:19

Blake Gontar: Okay. So liquid streaming is the application of a fungicide, the same types of fungicides that we can apply as seed dressings in a liquid band, either in the furrow or on the furrow to prevent rhizoctonia. So this is just a different method for applying a fungicide where we're going to apply seed. Now it's not widely used at this stage, but growers are increasingly applying other inputs, such as trace elements or UAN, in a liquid band within a furrow. So it's becoming more common the technology, but not so much for fungicides. The real benefit in applying fungicides in this way is firstly, you can apply more because we're not limited by the surface area of the seed, nor are we limited by the toxic tolerance of that emerging seedling. And the second advantage that we have is that we can actually put the fungicide in two different places. So in all of the work that was done in developing this technology, the best responses were where we put some of the fungicide below the seed to protect the primary root system, that emerging root system, and then a second band on top of the furrow, which would wash in and as the secondary roots or crown root started to develop, that top band would provide some cover for those crown roots.

00:09:31:28 - 00:09:41:00

Shannon Beattie: How do you growers actually go about doing this in a practical sense? What equipment do they need? How do they do it? When do they do it?

00:09:41:02 - 00:10:51:17

Blake Gontar: Like just about every management tactic for a soil borne disease, you really have to make this decision prior to sowing. So that's true of seed treatments or variety choice or crop choice. Pretty well all soil borne disease management strategies have to be decided upon before you put seed in the ground. So liquid systems are the same, or liquid application of fungicides is the same, and probably more so because there's a fairly big process of putting a liquid system onto a seeder. But essentially, it's just a series of pipes connected to some sort of manifold and pump connected to a tank. There are several companies, including Liquid Systems SA, that have off the shelf conversion systems or liquid systems, to go on to a seeder. They can be put onto just about any type of seeder bar, and there's all sorts of configurations that can be applied. And in general, the majority of growers that are using this system have one or maybe two liquid bands that they can apply through each tyne or disk.

00:10:51:27 - 00:11:04:27

Shannon Beattie: Do you have any stats at all for us on how well this works in comparison to a traditional fungicide treatment? Any data that we know about, you know, greater yield responses or anything like that.

00:11:04:29 - 00:12:16:18

Blake Gontar: Yeah, absolutely. So there was a whole host of research trials that were conducted in the early 2010s that compared one particular product, which is the uniform product that was initially released as a liquid in-furrow option. And what we saw was that over a large number of trials, the net yield response in wheat was around about 0.3 of a tonne per hectare, and the net yield response was around about 0.45 tonnes per hectare, using uniform fungicide in a split application. That compared with some traditional seed treatments, which provided at best around about 0.1 of a tonne per hectare. The other thing we saw in those trials is that the liquid fungicide was more reliable. So those figures, I quote, are net yield responses or average yield responses. Across a large number of trials, we saw more significant beneficial impacts with liquid fungicides at more trial sites than we did with the seed treatments, which very frequently weren't effective at all.

00:12:16:22 - 00:12:29:18

Shannon Beattie: Looking at the other benefits than just yield, are there any side benefits? I guess in terms of like fungicide contamination or anything like that, that can also benefit growers by using this sort of system.

00:12:29:22 - 00:13:07:06

Blake Gontar: I think this is a really good question. I'm probably not the best person to speak on behalf of growers as to what they prefer to use, but I certainly know anecdotally that many growers are averse to seed treatments because their application or their integration is usually via the farmer themselves applying seed treatment in an auger and mixing this themselves. And frequently this produces dusts which we know are toxic, so they need to be careful and wear a lot of PPE. I would think that handling a liquid in a drum into a hopper can be done more safely.

00:13:07:09 - 00:13:18:12

Shannon Beattie: This research that we're talking about is a couple of years old now, is done a few years ago, but how relevant is it still for growers to be taking into consideration at the moment?

00:13:18:14 - 00:14:19:05

Blake Gontar: Well, I think it's increasingly relevant for a couple of reasons. Firstly, it does appear that the uptake of liquid systems generally is increasing, and that's probably more to do with the application of trace elements and nitrogen fertilisers than anything. But as the growers become more comfortable with the technology and the processes is generally, then adding additional lines for fungicide or mixing fungicides where appropriate becomes pretty achievable. The second reason why this might be very relevant is that we've just come out of an extremely dry, cold season across most of Western Australia and South Australia, into Victoria. So our observation would be that rhizoctonia will have benefited from that season, so we're likely to be heading into very high levels of rhizoctonia inoculum in those areas that are conducive for rhizoctonia.

00:14:20:10 - 00:14:26:16

Shannon Beattie: Is there anything else, Blake, that you would like to add that I haven't asked you about yet, that you think is important for our listeners to know?

00:14:26:18 - 00:15:07:17

Blake Gontar: I think the critical point to maintain is that whilst some of the alternative crops like pulses and canola certainly do suffer damage from rhizoctonia, they're not fully resistant. We do have lots of work that shows they do provide break crop benefits, so they are hosts, but they're not good hosts. So rotating through pulses and canola absolutely has been shown to provide a reduction in rhizoctonia inoculum. The yield loss tends to be worse in barley than in wheat. So rotation is really still the key for avoiding big losses from rhizoctonia.

00:15:08:15 - 00:15:12:24

Shannon Beattie: Blake, thank you so much for joining me on the podcast today. I really appreciate your time.

00:15:12:26 - 00:15:14:06

Blake Gontar: No worries. Thanks for having me.

00:15:20:24 - 00:15:39:29

Shannon Beattie: That was Blake Gunter from SARDO talking about controlling rhizoctonia in cereals by streaming fungicide. More information on this topic can also be found in the description box of this podcast or online at grdc.com.au. I'm Shannon Beattie and this has been a great podcast. Thanks for listening.