Effect of fungicide strategy on resistance

[Feldspar]

I went to a spring NIAB meeting last week where the effect of mixing actives, timing and fungicide dose was discussed. I think there are a number of doctrines floating around about resistance management that aren't wholly upheld by the evidence. At the very least, acceptance of the uncertainty surrounding the common assertions needs to be made more explicit.

To give an example, it was asserted that SDHIs must be partnered with a triazole product as well as CTL to avoid resistance developing to the SDHI. The goal of protecting the SDHI seemed here to be implicitly assumed to be the overriding goal.

It was also asserted that the use of a single application of and SDHI at T2 without a T1 would be a stupid thing to do. Again, the implicit assumption here is that a single use onto a possibly higher level of disease would be more likely to drive resistance faster than two applications onto possibly lower levels of disease.

Lastly, it is common supposed that higher doses of fungicides are needed to protect against resistance. The assumption here is that higher doses are better.

A lot of these assertions are stated as if they are self-evident, whereas it's pretty obvious that they aren't. Here are a few papers below which I think do a better job of putting a bit of nuance into what is a complex picture.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-03-13-0061-R
http://onlinelibrary.wiley.com/doi/10.1111/ppa.12558/full
https://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-04-14-0121-RVW

I've got a number of thoughts on this, but I'll put one out there for starters. Are we being asked to design fungicide programmes with the main aim of protecting the manufacturers' latest active to the detriment to the farmer? Yes, it would appear that mixing CTL or a triazole prolongs the life of the SDHI that it's partnered with, but at what cost to the triazoles? These are also very valuable actives to the farmer even though they don't make as much margin for the chemical companies. You could argue that the SDHI is also protecting the triazole, but what about this for a suggestion (which is unrealistic):

If you were an omnipotent benevolent dictator, what would be the best fungicide programme to protect farmers' long term interests, and would it be different to the programmes we have now? If you partner an SDHI with a triazole, let's just say it prolongs the useful life of that active by 2 years from 5 to 7 years. However, if you'd used epoxi for 5 years until it no longer became effective and then used the SDHI for another 5 years you would have reduced your annual fungicide spend and would have had a greater number of years of effective fungicide control.

 

[franklin]

I am firmly in the camp that says what *you* do will make *no* difference to the useful life of an active. It's not like weeds where your population stays (balers excepted) on your own farm. Wind will blow the spores all about.

You can do an awful lot with robust azole rates here in the (supposedly) dry east.

 

[Oat]

Diseases can mutate very quickly (just look at yellow rust in recent years), and new strains can develop. if you stuck with old chemistry like epoxi for 5 years, you might then find that when you switch to SDHIs, the new resistant strains have already developed, so SDHIs are immediately ineffective.

I think the best idea is to mix different modes of action. Ideally use multi-site inhibitor products, although these don't always offer the best control of some diseases. If you use several modes of actions, then if one product doesn't give good disease control, hopefully another product used at the same time will help mop up what is left, this then helps avoid resistance developing, as you not relying on one mode of action/product/chemistry. It is much harder to develop resistance to several modes of action at the same time, as one.

However, you do raise an interesting point about what may be the cheapest/cost effective approach.

 

[yellow belly]

The reading I give to the information is that ctl is as effective a protectant as sdhi but that sdhi has eradicant effects

I have since 2012 practiced a t 1.5 protectant spray this has the effect of protecting the 2nd leaf which is the second highest contributor to yield after the flag leaf
Why we keep using a protectant on the 4th leaf when it is often hard to hit and contributes very little to yield if the t 1 is timed accurately the exception is if you have grown a yellow rust susceptible variety planted early in the southern half of Britain
In 2012 because of yellow rust I treated wheat a 18 day intervals and had much less problems compared to those who struggled to get the t2 on early enough
If eradicant is needed and a t1.5 or properly timed t1and t2 is not possible it is because you need more spraying capacity or better organisation

I plan on a sdhi ctl anole at t 1 then ctl on 2nd leaf and the see what weather is happening for the amount of sdhi on the flag leaf

We should note that the flag leaf needs more spray practice was developed when a later eradicant sprays would give as good a control as protectant sprays this is not going to be the case going forward
In the late 70s1980s we did a gs31 spray then helicoptered a late flag early ear spray on around late may growing very big yields from very early planted very early varieties
Now with mostly later planted later varieties the crops are radically different so need different thinking
The trials results in the 90s using 1/4 rate 4 times gave as high a yield as the high rate flag spray

 

[Feldspar]

I am firmly in the camp that says what *you* do will make *no* difference to the useful life of an active. It's not like weeds where your population stays (balers excepted) on your own farm. Wind will blow the spores all about.

You can do an awful lot with robust azole rates here in the (supposedly) dry east.

I agree that what an individual does makes little difference on its own. I was thinking more about national scale strategies.

 

[franklin]

I was thinking more about national scale strategies.

Always at the mercy of the chap who does what he wants then. SDHIs will go the same way as strobs. In a few years time, they will be cheap mixer for brown rust, with a bit of greening effect added in.

The flipside is that the dose curves for using an SDHI could easily support them being used on their own, given that resistance is inevitable. Responsible? Not really. But who's the irresponsible - the one who does whats economically right, or the company that supplies the straight SDHI? If they were that worried about it, they would bundle it with an azole, then we could grumble about the price of their pre-mixes.

Unless something radical changes, it will be a litre of epoxi and a litre of azoxystrobin for T1, and a litre and a bit of Aviator for T2.

 

[Feldspar]

Diseases can mutate very quickly (just look at yellow rust in recent years), and new strains can develop. if you stuck with old chemistry like epoxi for 5 years, you might then find that when you switch to SDHIs, the new resistant strains have already developed, so SDHIs are immediately ineffective.

I think the best idea is to mix different modes of action. Ideally use multi-site inhibitor products, although these don't always offer the best control of some diseases. If you use several modes of actions, then if one product doesn't give good disease control, hopefully another product used at the same time will help mop up what is left, this then helps avoid resistance developing, as you not relying on one mode of action/product/chemistry. It is much harder to develop resistance to several modes of action at the same time, as one.

However, you do raise an interesting point about what may be the cheapest/cost effective approach.

My understanding is that it would not be the case that at the end of a triazole use period that there would be a level of resistance such that SDHIs were immediately ineffective. You need to apply the chemistry to drive resistance to a level where that active no longer gives effective control. See the three phases of resistance that are set out here: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3059.2011.02439.x/full.

It is not the case that if one product doesn't kill 100% of disease that its partner will clear up 100% of what is left. Also, it is quite possible to develop resistance to two actives at the same time. It might be slightly slower for each individual active than if they were each used in isolation, but it's still a concurrent process.

 

[Feldspar]

Always at the mercy of the chap who does what he wants then. SDHIs will go the same way as strobs. In a few years time, they will be cheap mixer for brown rust, with a bit of greening effect added in.

The flipside is that the dose curves for using an SDHI could easily support them being used on their own, given that resistance is inevitable. Responsible? Not really. But who's the irresponsible - the one who does whats economically right, or the company that supplies the straight SDHI? If they were that worried about it, they would bundle it with an azole, then we could grumble about the price of their pre-mixes.

Unless something radical changes, it will be a litre of epoxi and a litre of azoxystrobin for T1, and a litre and a bit of Aviator for T2.

I wonder how many acres of crop have to be sprayed with an "irresponsible" programme for it to make a difference? 2% of the total crop area? 10%? 20%?

 

[Brisel]

It's ok. The serviced agronomy customers will help keep the actives going for longer through a higher spend on multi ingredient mixtures

Runs for cover and straps the tin hat firmly on...

 

[Feldspar]

It's ok. The serviced agronomy customers will help keep the actives going for longer through a higher spend on multi ingredient mixtures

Runs for cover and straps the tin hat firmly on...

Arguably if they put fungicides on when they're not needed (OSR for example) then they'll drive resistance faster! Higher dose not better, at least not clearly so.

 

[Brisel]

@Feldspar what diseases are you referring to? Septoria Tritici or others like mildew & ramularia?

I'll play devil's advocate here. Rather than protecting the manufacturer's precious investment in new actives, why not protect grower's options for disease control? Tirazoles are under threat from the EU endochrine disruptor defintion. SDHIs are also single site. The European market is dead for new actives thanks to our regulations. It's all about GM plant breeding now which we'll never have access to. Why not manage the risk of an interntional problem (we're downwind of Ireland where they've already detected SDHI resistance in septoria) by adopting a better spread of fungicide attack using multiple modes of action?

Arguably if they put fungicides on when they're not needed (OSR for example) then they'll drive resistance faster! Higher dose not better, at least not clearly so.

Target site resistance develops more quickly under high doses...

With diseases like light leaf spot needing to be treated prophylactically, how do you overcome this? It's the same for septoria in wheat now.

 

[Oat]

My understanding is that it would not be the case that at the end of a triazole use period that there would be a level of resistance such that SDHIs were immediately ineffective. You need to apply the chemistry to drive resistance to a level where that active no longer gives effective control. See the three phases of resistance that are set out here: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3059.2011.02439.x/full.

It is not the case that if one product doesn't kill 100% of disease that its partner will clear up 100% of what is left. Also, it is quite possible to develop resistance to two actives at the same time. It might be slightly slower for each individual active than if they were each used in isolation, but it's still a concurrent process.

I agree with your comments, but you maybe misunderstood what I meant slightly. What I meant was that at the end of the triazole use period, you may find that all your neighbours who have been using SDHIs may have already bred some resistance into the local strains of diseases, therefore, although you may not have personally contributed, any spores from your neighbours which infect your crop may be a problem. Unfortunately, with diseases and insects, the problem isn't just confined to your fields, as it can be with weeds, so the strategies your neighbours use also has an affect on you.

You are correct that two different chemistries may not give a total of 100% control, so what one doesn't kill, the other may not always top up. There are so many variables depending on the exact strain of the disease and what resistance there is currently is, but hopefully in an ideal world using multiple active ingredients and products will give you more chance to control more of the disease. Unless you tested each active ingredient individually and knew exactly what the resistance profile was, you won't really know if 2 or more is better than one, but in theory there is a higher chance of better control with more active ingredients.

 

[SilliamWhale]

Always x2 sdhis here for me. No point not in the wet west. Resistance? Ah well ill use a new fungicide that comes out by then if not ill be in the same boat as everyone else

 

[Oat]

Always x2 sdhis here for me. No point not in the wet west. Resistance? Ah well ill use a new fungicide that comes out by then if not ill be in the same boat as everyone else

I think I'm going to cry. I don't doubt that you need 2x SDHIs, but just because everyone else may have the same problem of resistance in the future, it doesn't mean you should still accept it.

A new product/chemistry will probably cost £££, so if you can eek out the control from existing chemistry a bit longer, it might help your margin. In practice, it may not make a massive amount of difference, if your neighbours take a similar as you currently do (as resistant disease can spread to you from them and vice versa), but it doesn't mean you shouldn't try. If everyone made more effort to manage resistance, maybe the future would be brighter.

 

[SilliamWhale]

I think I'm going to cry. I don't doubt that you need 2x SDHIs, but just because everyone else may have the same problem of resistance in the future, it doesn't mean you should still accept it.

A new product/chemistry will probably cost £££, so if you can eek out the control from existing chemistry a bit longer, it might help your margin. In practice, it may not make a massive amount of difference, if your neighbours take a similar as you currently do (as resistant disease can spread to you from them and vice versa), but it doesn't mean you shouldn't try. If everyone made more effort to manage resistance, maybe the future would be brighter.

It rains pretty much every day here. I could pretend i may possibly may not use an sdhi at t1 but theres an 80% chance i will. If it was exceptionally dry i may not but thats very uncommon. Beyond that what do you suggest i do?

Maybe we should have had stewardship guidelines from the manufacturers about only using sdhi's once a season but we dont and theyre pushing sdhi x2 anyway!

P.s. not saying im not using triazoles and ctl in good measure at same time.

 

[Oat]

It rains pretty much every day here. I could pretend i may possibly may not use an sdhi at t1 but theres an 80% chance i will. If it was exceptionally dry i may not but thats very uncommon. Beyond that what do you suggest i do?

Maybe we should have had stewardship guidelines from the manufacturers about only using sdhi's once a season but we dont and theyre pushing sdhi x2 anyway!

P.s. not saying im not using triazoles and ctl in good measure at same time.

As I said, I don't doubt you need 2x SDHIs. As long as you not relying just on SDHIs, but are also using triazoles and CTL (like you say), at least you are doing something

 

[SilliamWhale]

As I said, I don't doubt you need 2x SDHIs. As long as you not relying just on SDHIs, but are also using triazoles and CTL (like you say), at least you are doing something

Sure i presume most farmers are arent they? Do you not use two sdhis?

 

[Oat]

In the past I have used SDHIs at T0 if the situation demanded it, but yes, I have used 2x per season on most fields. Although occasionally, I have managed to not use any (good variety, good year, low disease pressure).
Like most people (hopefully), I have mixed SDHIs with other products

 

[Grass And Grain]

Many of these fungicides are expensive.

So what do we do? Use 50% rate, as trial data has told us that 50% rate does the job.

Full rate was not really economic to use, half rate was economic.

Result = resistance.

If the fungicides were priced correctly to start with, then we could all have used full dose rates.

I know that had simplified things a bit, but I suspect it is maybe a factor. Same story with lots of herbicides. There isn't much alternative to Axial on barley for wild oats, so we cut rates, then get resistance.

I think the manufacturers might have caused (or at least exacerbated) fungicide resistance by greedily pricing the product incorrectly in the first place. Chemical companies may have shortened longevity of their products due to their own desire for short term profits.

Half priced product with a minimum dose rate might be a way forward for future actives.

Edit. As individual farmers we can't use full rate product at current prices which are set too high. We can only do it if the chemical is priced sensibly in the first place.

 

[Brisel]

If you want to keep the actives, don't cut the rates. Simple. Otherwise you take your chances with the rest of us using less than full rate with the associated risks.

Growers won't collectively work together to manage the production, supply and marketing of grain so I don't see how this would work for fungicides. The only area that seems to be working is by collective buying of sprays. Fungicide costs go up each year because of decreasing efficiacy - prices for agchems have risen much more slowly than for other farm inputs. Have a look at the Anglia Farmers Agflation index.

Source: http://www.fwi.co.uk/business/farm-costs-now-rising-faster-than-inflation.htm

Yes, I know this is a 2011 article but that's all a quick search threw up.