BGTF Podcast: The facts behind resistant black-grass

Read the transcript of the podcast below.

Dr. Black Grass: “Hello, and welcome to Dr. Black Grass on air. This is the first series of podcast this harvest. Perhaps you are listening on the combine or at home, but wherever you listen we will bring you some of the latest information on black-grass control as well as a range of different harvest news. Each week we will be looking at a different topic affecting black-grass control. This week, it is resistance to herbicides. Herbicide resistance is a big concern internationally with many countries having their own problem weeds. In the UK, it is undoubtedly black-grass, so considerable time and expense has been put into understanding this issue. One of the biggest projects is the BBSRC black-grass resistance initiative. And I caught up with project leader, Dr. Paul Neve, at Cereals.”

Dr. Neve: "We are really trying to understand the evolution of herbicide resistance, right from the level of fundamental genetics and biochemistry through to management in the field. One of the major things we have been focusing on in the first year of the project has been what we term the 'National Resistance Audit'. So this has involved working with farmers, contacting farmers, and asking them if we can come onto their farm, mapping black-grass populations on their farm, and just building up a picture of the scale of the black-grass problem. As well as mapping fields, we are collecting seeds from those fields, and those seeds are being tested Rothamstead for resistance to key black-grass herbicides. On top of that we are also collecting field management history for each of those fields, so we are trying to collect all the data we can about how those fields have been managed over the last 10 years, so that provides us with a picture of where farmers and individual fields are at in terms of black-grass, what is the resistance status of those fields, and what have farmers been doing over the last 10 years to bring them to that situation? So we hope that we can use all that information to start to of tease apart what has worked and what hasn't worked in terms of management, and of course over the 4 year course of this project we will keep going back to those fields to see how the problems have been developing, we will ask farmers what they have been doing over those intervening years and again try to build up a picture of what is working, what isn't working and how the problem is changing over time."

Dr. Black Grass: “Okay, so are populations of black-grass consistent in their resistance status? Or do you get mixed populations?”

Dr. Neve: "It's a good question, and I have to say that at this stage we do not know, because essentially what we do is that we collect seeds, and we collect seeds from 10 random locations within a field. This year what we have done is just bulk those collections and look at resistance across all fields. The average picture if you like. What we may be able to do in the future, because we still have the 10 independent population from each field, is to go and look at the regional variation, or variation across a field, but that is not something that we have looked at so far."

Dr. Black Grass: “A big question that often comes up is the fitness penalty to being resistant, but it’s never really been established, that is, if there is a fitness penalty. Also sometimes resistant types might seem more vigorous than non-resistant - can you tell us anything about that?”

Dr. Neve: “That is another element of this project. What I can say is that we are particularly interested in 'non-target-site resistance' or 'metabolic resistance'. I worked for a number of years in Australia where the major weed is rye-grass, and what we found with rye-grass is with its metabolic resistance, there was about a 20% fitness cost. In other words, resistant plants produced 20% less seed than susceptible, so we are interested to know if that’s the case for black-grass. I don't think it’s necessarily going to solve the problem for us, but it’s good to know if resistant black-grass does have an Achilles’ heel which we may be able to exploit."

Dr. Black Grass: “And finally, you have mentioned that there are two different resistance types. Which one is more problematic for UK growers, or is there a combination?”

Dr. Neve: "What we found from previous research is that in most populations there tends to be some level of metabolic resistance. What we also found was that in many of those populations they also had 'target-site resistance', so actually the two mechanisms are co-occurring in populations. I believe that metabolic resistance is the bigger problem, because target-site resistance gives you a very specific type of resistance to one herbicide mode of action, whereas the metabolic resistance can give you a very broad spectrum of resistance."

 

Dr. Black Grass: “So that could be problematic to deal with using chemistry for years to come, even if we develop new chemistry?”

Dr. Neve: “Yeah. What some people say is that these resistant black-grass populations may be resistant to herbicides which have not even been found yet because they have this broad spectrum of resistance.”

Dr. Black Grass: “Okay. With that in mind, what would you imagine some of the solutions might be?”

Dr. Neve: "I think some of the solutions come down to economic practices, so I think we have to be aware that there probably aren't any new herbicides on the horizon; any silver bullets. So I think getting more spring crops into rotations – black-grass doesn't do well in spring crops. We know that delaying drilling in autumn, so sowing autumn crops a bit later gives added opportunity to control black-grass before the crops are drilled. And looking further into the future, we are becoming increasingly interested the potential of allelopathy to potentially help us manage black-grass. Whether GM or new crops with resistance to broad-spectrum herbicides could have a part to play. I think if that does come onto the agenda in the future we have to be very careful how we use those crops, but I think they could have a part to play. I think a lot of the immediate and pressing problems we are having, they are just agronomic solutions, such as thinking about wider rotations and less autumn sowing of crops."

Dr. Black Grass: “Thank you Paul. So Paul’s concern is that enhanced metabolism resistance can give plants the ability to deal with herbicides in the future, as well as in the present. However, I spoke to Gordon Anderson-Taylor of Bayer CropScience, and he thinks that we should also be worried about target-site resistance in the here and now. This is because it can make our existing chemistry ineffective.”

Gordon Anderson-Taylor: "I think like all growers who are concerned about resistance to any black-grass products, it is essential to be able to control black-grass, and when we start to lose the chemical control it becomes very difficult to do it by cultural methods, so we continue to monitor resistance with all our products, grateful, really, for the fact that today we’ve not detected any resistance to our lead product for black-grass control, Liberator. But clearly we have got resistance to Atlantis occurring throughout the countryside. However, it is important to keep it in perspective in terms of resistance to products such as Atlantis or other ALS inhibitors; in fact, whilst most people say the efficacy is declining, there’s large hectareges where it remains effective. Where it isn't effective, clearly we need to have a resistance test done and identify the form of resistance present. Once you know exactly what form of resistance is present it may give you some help in indicating what the appropriate form of chemistry is that you should use, or perhaps the timing of application that should go with your Atlantis."

Dr. Black Grass: “Okay. And what are the different types of resistance?"

Gordon Anderson-Taylor: "The two main sorts of resistance present, particularly in black-grass but also in other things such as rye-grass to some extent, are the enhanced metabolism resistance (and the basis of enhanced metabolism is essentially the enzymes in the plants are, dare I say, hiked up and enable the plant to break down a whole range of herbicides). The other major form of resistance is the target-site resistance which is where there is actually a change of the enzyme binding site, so the herbicide can no longer actually bind to the enzyme and it becomes totally ineffective. Clearly out of these two mechanisms, the target-site resistance is the one that’s of most concern and that is the one that affects the chemistry such as the ALS inhibitors, such as Atlantis, or indeed the ‘fop’ and ‘dim’ herbicides."

Dr. Black Grass: “Clearly then both types of resistance are a problem, and there is clearly a debate about which is the biggest threat. But when it comes down to farm-level management, the principles are the same. Here is Gordon Anderson Taylor again.”

Gordon Anderson-Taylor: "I think when you look purely at chemistry the importance is rotation and modes of action, and if we are thinking of something like black-grass, you would be wanting to mix and match your chemistry so you start off with flufenacet-based materials such as Liberator, before following with your Atlantis so at least then you have different modes of action present. Outside of different modes of action it is important to start thinking about cultural control, because if you can almost forget about the form of resistance, if you’ve got a high population of black-grass, whatever the form of resistance, you need to get that population down to a manageable level - something that is manageable with the chemistry that is available - so really you have got to adapt techniques such as either cultural control, or introduce spring cropping. Again, these give you opportunities to control emerged grass weeds that come up in the autumn, but also essentially the process prevents development of black-grass in the following spring crop.”

Dr. Black Grass: “What would you say is a manageable population?”

Gordon Anderson-Taylor: "Essentially with something like black-grass it is a zero-tolerance weed. In terms of populations which can be tolerated in theory to not maximize yield loss, there are recorded levels, but if you are looking at long-term viability, most businesses want to maintain the maximum level of control so it is really a zero-tolerance weed."

Dr. Black Grass: “Sometimes people talk about having Atlantis holidays to minimize development of resistance in the population, is that a good idea?”

Gordon Anderson-Taylor: "No, not really. I think if you talk to all the experts - the resistance that you’ve got in the population – it just doesn’t go away. So the fact that you don't use an herbicide doesn't mean that the resistance to that herbicide actually goes away. So, no there is no point in having an Atlantis holiday. In fact, if you were to have an Atlantis holiday and because of that you achieve lower levels of control, all you would then do is return more seed perhaps to the soil profile, and again that will cause problems for the future and it will still be the same degree of resistance as the existing population."

Dr. Black Grass: “Okay. And finally, parts of the country (Cambridge, Lincolnshire, Oxfordshire) have serious problems, but even further west and further north they’re starting to come across black-grass. Some people say it's moved in on machinery and so on from other parts of the country. What advice would you give to farmers who are maybe just beginning to see the weed in their crops and are a little bit concerned?”

Gordon Anderson-Taylor: "I think they quite rightly need to be concerned, I think the classic is Yorkshire, and certainly we hear a lot of people talk about black grass on their farms. And what this says is that they are well aware hopefully of the threat, they know what goes on in these other counties, and basically, tackle it in a robust nature from early on. So if you see the odd black-grass plant, obviously you can get in there and hand rogue it; if it is more than that you can still spray small patches of black-grass just to prevent the seed return. If you’re looking at chemical programmes perhaps be a little bit more robust initially rather than relying on limited chemical programmes just to keep on top of it. So basically, be robust with your approach from the start to prevent development and spread of those populations."

Dr. Black Grass: “Thanks a lot Gordon, some useful tips there on how to deal with black-grass on farms, and we will be carrying on this theme next week with a look at two case studies of two farms that have dealt with some really tricky black-grass, and we’ll also be thinking a little bit about cultivations. Before we sign off there is still time for a little bit of harvest news - it's still only the 22nd of July so only the first winter barley and oilseed rape crops are coming in, and we don't have any news yet on yield and quality. But if you see anything interesting coming off the combine or if you want to talk about anything that we have discussed on today's show, please tweet us @DrBlackGrass. That's all for this week and we hope you listen to the next Dr. Black Grass on air available Wednesday the 29th of July. Goodbye.”

 

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