Ben Taylor-Davies black grass talk

[Feldspar]

Ben came to talk at our local discussion society yesterday and gave a very interesting talk. In particular, there were a few points that I wanted to think about further.

So, for the first one, Ben said that following his Nuffield tour and speaking to weed experts (whose names I have sadly forgotten) that it is a myth to suggest that sequencing of actives with the main purpose of the first softening up the plant for the second to give better results is a valid strategy. His claim was that the first stresses the plant out so much that it then does not take in as much of the second chemical thus producing poorer results from the second compared to if it had been used alone.

The analogy he used was that of sequential gates with the openness of the gate representing the ability of the plant to take up a herbicide. Application of the first active partially (to some extent) closes the subsequent gates. The second active then applied is partially blocked by the part-open gate and so does not all do its intended job. Ben said that the predominant narrative is that of sensitisation; the analogy here being that it is easier to knock someone over when they are already staggering from being bit before.

Both narratives are on the surface plausible, but which is true? Ben seemed to be a fan of being guided by the experts and the evidence. A laudable philosophy. So what is out there to support this idea?

There seems to be a lot of patent applications out there which claim synergistic effects from mixtures of herbicides -- i.e. the effect of the actives used together is greater than the sum of the effects of the actives used individually. Here's one example: https://patents.google.com/patent/EP2597956A1/en, and there are a number more.

Away from patent applications, there is evidence on both sides of the argument. This is one of the most relevant studies that I could find: https://www.cambridge.org/core/jour...ious-studies/C845D938A3A248D7BD36A7BD82E859CC.

The key sections from this paper are, IMO:

- "Collectively, the relative frequency of occurrence is 67% (N = 322) for an antagonistic but only 33% (N = 157) for a synergistic interaction in previously conducted studies."
- Antagonism dominated in studies of plants from the Compositae, Gramineae, and Leguminosae families.

So, I would say from this that is not correct that it is a total myth that synergism exists between herbicides. However, it is to correct to say for black grass that antagonism is more likely than synergism.

For black-grass there is scant work done on synergism between different actives. The only thing I could find after a quick search was this: http://agris.fao.org/agris-search/search.do?recordID=US9312308. However, this is more an adjuvant-active synergism rather than an active-active synergism.

 

[SilliamWhale]

I suppose another way of looking at it is a pesticide is either good at killing something or its not. Some pesticides are better at killing some things than others (obviously). If you look at the charts from say NIAB or the chem companies you will often get say 80% control using one active but the extra control from the second active isn't necessarily a great leap forward even if you could have used the actives the opposite way round.

I doubt the herbicides are synergistic per se, its like saying radiotherapy and chemotherapy are synergistic when really they are two separate things having a go and ameliorating the same problem

Also what are survivors going to do? In many ways the pool of herbicides for in crop spraying of weeds and plants from the same family is a small pool really.

 

[farmerfred86]

His Nuffield report is a good place to start but I assume you will have read that already.
His argument is surely for follow up applications? As the plant is stressed and less able to take up the second application. For the initial herbiced “stack” the plant takes in all of the presented actives as it is still healthy.

So the question is surely do follow up applications work? I would say they rarely do (as per my recent question about using axial on winter barley for young BG control)
We have always put that down to “the weed is too big” or too deep rooted but perhaps the plant is too stressed?

 

[Feldspar]

I suppose another way of looking at it is a pesticide is either good at killing something or its not. Some pesticides are better at killing some things than others (obviously). If you look at the charts from say NIAB or the chem companies you will often get say 80% control using one active but the extra control from the second active isn't necessarily a great leap forward even if you could have used the actives the opposite way round.

Also what are survivors going to do? In many ways the pool of herbicides for in crop spraying of weeds and plants from the same family is a small pool really.

First paragraph is true but is it not beside the point? I.e. it doesn't matter what the % control of each is individually (low or high), it's the effect of both together or in either order that's relevant here. That said, I too was thinking about charts with supplementary BG control. Here I don't think the aim is to get synergistic control. I think we are all realistically hoping for additive control at best. To put on flufenacet and then aim to wait until all emerged black-grass to look healthy and unstressed before applying pendimethalin is not likely to be a workable strategy because both work pre-em of the weed (even if there is some antagonism between the two).

Second paragraph, I'd just say that within the black-grass herbicide family there are a choice from herbicide groups (a classification that is woefully underused according to Ben). Avadex is a different group to FFCT.

 

[SilliamWhale]

Would Liberator not be a synergistic package anyway?

 

[Feldspar]

His Nuffield report is a good place to start but I assume you will have read that already.
His argument is surely for follow up applications? As the plant is stressed and less able to take up the second application. For the initial herbiced “stack” the plant takes in all of the presented actives as it is still healthy.

So the question is surely do follow up applications work? I would say they rarely do (as per my recent question about using axial on winter barley for young BG control)
We have always put that down to “the weed is too big” or too deep rooted but perhaps the plant is too stressed?

I did read his report a long time ago, but I ought to reread to see if my questions have already been covered.

I understand the point about follow-ups versus stacking simultaneously and you're right that he was mainly talking about the former. It raises a question which I don't know the answer to; that is, when NIAB present their nice chart about supplementary control from other actives, are they following or applied at the same time as the base 240g of FFCT? @Fromebridge?

 

[Feldspar]

Would Liberator not be a synergistic package anyway?

Not obviously so (as in I've not heard that claimed).

 

[Feldspar]

One of his other very interesting discussion points was the speed at which black-grass populations adapt to local conditions. He talked about the ability of a population to quickly (less than 10 years and possibly less than 5 IIRC) adapt to repetitions in farming systems. For example, if you no-till for a number of years, you will select for black-grass plants which tend to have higher germination rates in unmoved soil and lower germination rates in moved soil. This occurs, he said, to such an extent that if you then put a cultivator through a no-till field with an adapted BG population, you will see less black-grass germinating in the moved area than compared the unmoved.

Same occurs for regular spring cropping. If you have a high black-grass population, do not kid yourself that continuous spring cropping will be a permanent answer because before too long you'll end up with more spring germinating black-grass and have the same problem but at a different time of year.

He showed some pictures and some graphs showing changed germination rates throughout the year in different systems. Illustrative but not conclusive. I'd be interested to know what detailed evidence is out there for black-grass on this. He introduced work done though in other weeds to show how quickly they adapt which did add to the strength of the argument.

Overall, I thought this strand of the talk was really interesting and a good way of thinking through the problem.

 

[ajd132]

Find his report interesting but part of me thinks his theories are massively over complicating it all.

 

[ajd132]

One of his other very interesting discussion points was the speed at which black-grass populations adapt to local conditions. He talked about the ability of a population to quickly (less than 10 years and possibly less than 5 IIRC) adapt to repetitions in farming systems. For example, if you no-till for a number of years, you will select for black-grass plants which tend to have higher germination rates in unmoved soil and lower germination rates in moved soil. This occurs, he said, to such an extent that if you then put a cultivator through a no-till field with an adapted BG population, you will see less black-grass germinating in the moved area than compared the unmoved.

Same occurs for regular spring cropping. If you have a high black-grass population, do not kid yourself that continuous spring cropping will be a permanent answer because before too long you'll end up with more spring germinating black-grass and have the same problem but at a different time of year.

He showed some pictures and some graphs showing changed germination rates throughout the year in different systems. Illustrative but not conclusive. I'd be interested to know what detailed evidence is out there for black-grass on this. He introduced work done though in other weeds to show how quickly they adapt which did add to the strength of the argument.

Overall, I thought this strand of the talk was really interesting and a good way of thinking through the problem.

When I read all this I concluded a good mixture of spring and winter crops with variation between no till and cultivated crops should be the realistic answer to this on an actual working farm.

 

[Feldspar]

Find his report interesting but part of me thinks his theories are massively over complicating it all.

I thought his overarching thesis of fast adaptation as an explanation for a lot of problems we (unwittingly) get ourselves was in a way simplifying because it brings together a lot of separate areas such as herbicide strategy and cultural controls under one unifying umbrella.

 

[ajd132]

I thought his overarching thesis of fast adaptation as an explanation for a lot of problems we (unwittingly) get ourselves was in a way simplifying because it brings together a lot of separate areas such as herbicide strategy and cultural controls under one unifying umbrella.

Yes I totally agree with that.

 

[Feldspar]

When I read all this I concluded a good mixture of spring and winter crops with variation between no till and cultivated crops should be the realistic answer to this on an actual working farm.

His suggestion of purposely driving the population to adapt by repetition (rather than constantly changing things) and then a sudden and lasting change (at least for a while) I think has merit to it.

 

[ajd132]

His suggestion of purposely driving the population to adapt by repetition (rather than constantly changing things) and then a sudden and lasting change (at least for a while) I think has merit to it.

Isn't that what's happend on most farms anyway?

 

[ollie989898]

I would love to able to conduct my own controlled assay of herbicide effectiveness, without any interference from any chemical company. I'd soon find out how effective these actives actually are. I bet 50% of them have less than 50% efficacy on black-grass before you bring resistance into the equation.

 

[Feldspar]

Yes I totally agree with that.

I think his BEN system is put slightly differently to the way I've seen it before in that I think he would suggest pushing on through with a system even with higher black-grass numbers to force it to adapt away from an old system, whereas many would chop and change at the first sign of trouble, but that may be a mischaracterisation. Agrii from their Stow Longa work have got something that looks in terms of prescription similar in their cultivation strategy -- i.e. shallow cultivate for a while and then plough -- but I think with a different conceptual framework.

 

[Feldspar]

Isn't that what's happend on most farms anyway?

Not exactly. A lot of farmers think that if they go to permanent spring cropping that that will continue to provide the +73-95% (or whatever it is) cultural control for year on year. Ben would say that after a while that figure will reduce significantly.

He also gave the example of delayed drilling and claimed that this would only work for a while. He claimed to have seen where this was done for a while until selection had occurred for later germinating plants so that the effect of the delay was much reduced and with less time for the crop to grow and be competitive.

 

[Gong Farmer]

Not had time to read all the links but agree of two sequential applications the first works far better than the second because a smaller plant encounters it. Second ones aren't as effective but they are there in case anything survives the first. If as he says the first prevents the plant from taking up the second then that's fine, it has been affected by the first. If it recovers it is likely to be more prone to taking up the second (by his logic?) Either way you get a dead or very ill target plant, who cares how it died?

 

[Feldspar]

Not had time to read all the links but agree of two sequential applications the first works far better than the second because a smaller plant encounters it. Second ones aren't as effective but they are there in case anything survives the first. If as he says the first prevents the plant from taking up the second then that's fine, it has been affected by the first. If it recovers it is likely to be more prone to taking up the second (by his logic?) Either way you get a dead or very ill target plant, who cares how it died?

He is claiming that putting Atlantis on in the autumn when the plant has been "sensitised" by the pre-em stack is wrong because the plant won't take up the Atlantis though. I think my point would be that you can't not put the pre-em on, in which case you either put it on in the autumn when it's stressed (and might not work as well) or in the spring when it's bigger (when it won't work as well). NIAB work supports the autumn application which suggests that it's better putting it on when it's stressed rather than when it's tillered (both of which are likely to increase resistance compared to if it wasn't tillered or stressed).

For those charts showing additional control of actives, are they applied sequentially or concomitantly with the base treatment?

 

[ajd132]

Not exactly. A lot of farmers think that if they go to permanent spring cropping that that will continue to provide the +73-95% (or whatever it is) cultural control for year on year. Ben would say that after a while that figure will reduce significantly.

I meant many were permanent wheat wheat osr min till then jumped to two or three spring crops then back into wheat? I really do agree with how quickly it adapts and having a decent rotation of spring and winter crops along with a couple of soil health boosts establishment techniques should go a long way to keeping it in check as long as you stick to a diverse plan? Difficult one, his report really does make you think.