Fungicide futures 2019

Jason Pole, AHDB Communications Manager, interviewed Paul Gosling for a podcast episode on fungicide futures. Here’s the transcript of that interview.

Q1. Paul, welcome back! Let’s start with some basics. What is fungicide resistance and what causes it?

At its simplest it’s a heritable change in the fungus that reduces its sensitivity to a fungicide. It arises due to natural variation caused by genetic mutations. The important thing to remember is that it does not necessarily affect disease control in the field. It depends on how strong the resistance is and how frequent it is in the population. That’s something for people to remember when they read or hear about fungicide resistance.

Q2. Fungicide performance takes centre stage at AHDB Agronomists’ Conference each December. NIAB’s Stuart Knight provided us with an update on fungicide performance this year. So what’s the picture, when it comes to fungicide sensitivity shifts in the UK pathogen population?

Well despite the fact that disease pressure was generally low in 2018 because of the hot dry summer we still saw a shift in the sensitivity of septoria populations, particularly to SDHIs. The shift was not dramatic but it continues the trend we have seen over the last few years. We can now quite clearly see a shift in the performance of both solo SDHIs and SDHI azole mixtures in our fungicide performance trials, though performance of commercial programmes in 2018 was good. For other diseases with evolving resistance such as net blotch we don’t do so much testing, but field performance appeared stable, so any changes that did occur were again not dramatic.

Q3. Let’s talk about the new publications now. I understand AHDB has issued two new publications as part of its collaboration with the Fungicide Resistance Action Group UK. Why did you team up and what does the guidance look to do?

The UK FRAG does an excellent job of gathering the latest information on the resistance status of crop pathogens and formulating advice, but it has very limited resources. We knew there was evolving resistance issues in a number of cereal pathogens, plus potential loss of some key actives that could have a big impact on disease management in cereals. So we decided we needed to raise the profile of resistance management and provide clear anti-resistance messages that the industry could agree on. The collaboration does this, it allows us to use AHDBs comms resources to bring industry agreed anti-resistance messages to growers and agronomists.

Q4. The topic of Integrated Pest Management is creating somewhat of a buzz at the moment. Balancing the use of chemical and non-chemical control methods has always been a challenge. This new guidance puts varietal resistance as the foundation of any fungicide programme. Although this sounds like a sensible plan, it’s not simple, is it? So, what are the strengths and weaknesses of this approach?

Well Jason, I wouldn’t say using varietal resistance is complicated, but historically more resistant varieties had a significant yield penalty and we have also seen the sudden breakdown in variety resistance to rusts from time to time. This tended to put growers off reducing fungicide rates. But the yield penalty is much less in wheat now. The big question still is how far you can cut fungicide use with more resistant varieties and still have good disease control. We have good evidence from research over the last few years that azole plus multisite is sufficient at T1 in the more resistant wheat varieties, but you probably still need an SDHI at T2.You can probably drop T0s as well, but we have not done the research to show this. The issue for some growers is that relying on fungicides for controlling disease has proven a very effective and profitable way of growing in cereals in the past so they are reluctant to change. But I think with new the new varieties with 7s and now even an 8 for septoria on the RL its time to look again at how we manage disease in wheat.

In barley it’s a bit different, the breeders are behind wheat in developing varietal resistance, as we’ve seen with the withdrawal of the RL ramularia ratings, but there are still more and less disease susceptible varieties, giving some flexibility in disease control options.

Q5. Beyond varietal resistance, what are the other key cultural controls?

There a wide range of things growers can do to reduce disease pressure. There are the obvious things like removing the green bridge and trash and diversifying the rotation. But some growers may not realise that delaying wheat drilling to mid October makes a big difference to septoria pressure in the spring and fits well with black-grass and BYDV control. If people want to try something different we know variety mixtures can reduce disease pressure, its used a bit in organic farming, though there are obvious challenges with this approach.

Q6. Farming without chemistry is still a long way away for most of the industry, as it looks to keep up with global demand for cereals. So let’s turn from cultural options now, to chemical. What’s the latest guidance, in terms of when and when not to treat?

I don’t think anyone is going to question the key T1 and T2 fungicide timings in winter wheat and barley. There is a strong yield response in all but the most extreme circumstances. But growers really need to think about the T0 and T3 timings and ask if the disease pressure warrants treatment at these timings, especially in more resistant varieties, as yield response is usually small but selection for resistance still occurs. As for T1.5 or T4, T5 there really shouldn’t be need for these treatments. If people are using these on a regular basis I think they need to ask some difficult questions about the way they are managing crops.

Q7. So a treatment decision has been made. What about getting the dose right? And do the rules hold true for both wheat and barley?

Pretty much. Research done over that last five years or has shown that dose has a much smaller effect on selection in fungicides undergoing slow shifting selection, like azoles and septoria, than it does on single step of big step changes, like strtobilurins and septoria or SDHIs and septoria. So what that means in practice is that its safer, from a resistance management point of view to increase the rate of the azole component of a septoria programme than it is to increase the SDHI component. Buts its not always straight forward as that, because until resistance appears and we can characterise it we don’t know if its going to be slow shifting or single step, but as a rule of thumb, don’t use any higher dose than you need for disease control, both from a resistance point of view, but also an economic, as the dose goes up the economic return gets less.

Q8. Although dwindling, there are still several modes of action out there and they all play a role in protecting efficacy and getting good control.  The Fungicide Futures guidance gives to useful information about the pros and cons associated with mixing and alternating them. So what’s the best way to balance the fungicide programme?

With the single site acting fungicides, the azoles, SDHIs, strobilurins, morpholines and the like, its about diversity. So for instance in barley, the default can be to go to prothioconazole and the SDHIs, they are very effective, but others including strobilurins, cyprodinil, the morpholines can all contribute to control of the key barley diseases and ease the selection pressure on the SDHIs and azoles. In wheat it’s a bit more difficult because for septoria there are limited options, but where rust is the target strobilurins still give god control and are an alternative to azoles, because even if its not the target, if septoria is there you will be selecting for more resistance stains if you use an azole.

Q9. We touched on the use of multi-site chemistry last time we spoke. Why is it so useful and how should multi-sites be best deployed across the spray programme?

Multi-sites can and should be deployed across the programme. They can substitute for single sites in some cases and of course with ramularia in barley, chlorothalonil is the only active left with significant activity. Where used in mixture with single site actives they reduce selection against the single site and they also add useful efficacy, especially against septoria.

Q10. When it comes to planning sprays this season, what do you see as the single most essential ‘must-do’ for 2019?

In wheat, its multi-sites. They will help slow further selection for resistance to azoles and SDHIs in septoria and add efficacy against septoria. In barley, I’m going to cheat and have two, first its diversity of actives, keep the pathogens guessing, second its chlorothalonil at T2 for ramualria control. Its very low risk for resistance an essential to keep ramualria out.

The Fungicide Futures publications, as well as the latest fungicide performance data, can be accessed via the AHDB website: ahdb.org.uk/knowledge-library/fungicide-performance

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Paul Gosling

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