BGTF Podcast: Finishing the programme: Post-ems

Read the transcript of the podcast below.

Podcast 6

Dr. Blackgrass:            Hello. This is the sixth and final episode of Dr. Blackgrass on air. Today we'll be hearing about post-emergence herbicides and how getting drainage fixed can help you apply them at the best time. First off, I spoke with Phillippa Overson and Ben Coombs of Bayer CropScience about when and how to apply Atlantis WG.

                                    If people have applied pre-emergence herbicides and they've got very good performance from them, is it still worth going in with a post-em spray?

Phillippa:                     You can achieve a lot of black grass control with either cultural controls or a well-timed, well-applied pre-em. Those are very important parts of the program, but you can only ever really get that towards the 80% control mark even if you do a really good job, so it is usually going to be worth coming back in with a post-em at some point in the program.

Dr. Blackgrass:            What is the ultimate timing for a post-em spray of Atlantis?

Phillippa:                     It's not so much dependent upon the time of year. What you need to get Atlantis to work best is to make sure you are targeting the weeds when they are very young. One to three leaves is preferable and the other important thing to remember is that the weeds need to be actively growing; it's best not to spray following a really, really cold snap. You do need the plant to be active enough to take the chemical in, in order for it to work.

Dr. Blackgrass:            Okay, and a lot of people now delay their drilling into late October. Would this mean that spraying Atlantis in autumn time is probably not likely and it will have to wait till spring?

Ben Coombs:               In the last ten years, or so, the distinction is often been between autumn or spring application for Atlantis and that has kind of changed a bit with the increase in delaying drilling. The likelihood of enough black grass in a field getting to the one to three leaf stage is less likely if you have delayed drilling to late October. You are more likely to actually get the target emerging in the spring. It really depends on whether the target is there in the autumn rather than defining by calendar date.

Dr. Blackgrass:            Obviously spring is quite a broad term that can mean any time from February to early May in some people's book.  What kind of time in spring should you be aiming to spray?

Ben Coombs:               Again, this is really dependent on size of weed - much more important than calendar date. If the opportunity arises in January or February, that's the time to spray. If you’re shut out because of the weather, then the point is a little bit moot, but the earlier you can go the better to avoid targeting weeds when they are large.

Dr. Blackgrass:            Often in spring the ground is very wet, water-logged, travel can be difficult. Maybe a grower will see the opportunity of a weed at the one to three leaf stage but isn't able to get on. What can they do about that?

Ben Coombs:               Yeah, it is going to be a really frustrating challenge, to be honest that. To be perfectly frank, the thing that needs to be done is remedial measures or measures taken well before you get to that point and having the land draining properly, having the soil structure to be such that you open up the ability to travel in more difficult conditions in the winter, is going to give you more opportunity to spray the weeds when they are at that two, three leaf stage, but equally, I certainly wouldn't be recommending getting a sprayer out into a field that is water-logged and trying to solve one problem - black grass - by causing another (structural damage to your soil). That is definitely not where you want to be.

Dr. Blackgrass:            Application of Atlantis, obviously, there is a few things you can do to make sure you get the most efficacy out of the product. How should growers apply?

Ben Coombs:               When we are thinking about Atlantis, it's a contact material and it is taken up by actively growing weeds. When you consider it in that context, what you need to be doing is getting the maximum coverage and the most even coverage you can achieve onto weeds that are dry and growing. A dry leaf is really important, so if you can avoid spraying while there's a significant amount of dew in the crop, that is going to really help you. Coverage comes from having the appropriate spray texture. We would recommend a medium fine spray texture where appropriate. And then speed of your sprayer is a really important thing to consider. The kind of magic figure is about 12k. If you can be at 12 kilometres an hour or lower, you are much more likely to get a nice even spray coverage. The faster the sprayer is going, the more difficult that is to achieve. Part of evening out the spray coverage as well, of course, if you use biopower tank mixed in with Atlantis, that will help with coverage and uptake of the herbicide into growing weeds. If you factor all of those things in together, you are more likely to get good coverage.

Dr. Blackgrass:            Finally a question for Phillippa ... Lots of people are hesitant about using post-emergence products now because of the perceived and the actual presence of resistance in that population. Is there anything they can do to manage that resistance risk with how they use post-emergence products?

Ben Coombs:               Yes, there is. Certainly the bulk of the resistance, we believe, in the UK population of black grass at the moment is enhanced metabolism. This obviously becomes stronger in the plant the bigger the plant gets, so making sure that you get the plant early in that one to three leaf stage is critical. As with anything that's making control more difficult, then close attention to application technique is going to help and making sure that you have taken every opportunity before the post-em spray to make sure you are targeting as small a population of black grass plants as is possible. If you think you have got a resistance issue, then it is usually a good idea to make sure that you have had a resistance test done so that you know exactly what you can and can't use in the field.

Dr. Blackgrass:            Thanks Phillippa and Ben. As pointed out by Ben, sorting out any problems with drainage during summer is an important step in allowing timely applications of herbicides. I spoke to soil specialist Philip Wright abut drainage. The interview was recorded over the phone so the quality isn't perfect but it’s worth listening to what he has to say. I started by asking by asking him about the benefits of getting drainage fixed.

Philip:                          If you get your drainage fixed then the rest of your soil structure, and to a certain extent, some of your weed control problems will actually be significantly improved, so it is certainly the biggest factor that limits good soil structure and particularly black grass control with it being a marshland weed.

Dr. Blackgrass:            I then asked Philip about how to maintain existing systems and identify land in need of drainage.

Philip:                          I think number one is maintaining what you've got. Making sure the drains, the outfalls are clear, and the ditches are clear to allow water into them and I know it sounds obvious, but there is many, many, many cases where the outfalls are actually below the bottom of the ditch through just siltation growing up and so then naturally those soil levels raising in the ditches and so the first stage is really to make sure the ditches ... You can see the outfall is clear and the ditch is deep enough to allow the water into it and that's the first step really.

                                    Second one would be to make sure the drains themselves are clear and running and can you jet them? Some drain systems are more difficult to jet than others particularly the herringbone type that don't have all the outlets into a clear ditch to be able to jet them. That becomes a challenge a little bit, but then if all of that is right or basically you have got a part of the field where it’s failed, often these days people just drain the problem rather than drain the field, so they’ll lead the water away from the low spot. Whilst doing that, it’s always good to question why that area is flooding in the first place. Is it because drains further away aren't intercepting the water anymore? If the field originally was drained well then there's normally a reason why now it has wet holes in it.  It is either part of the drain has failed or part of the system’s failed or you know in some cases it even can be they have amalgamated two fields into one and where there was a ditch now isn't any more. There probably isn't an appropriate system to take water from that point.

Dr. Blackgrass:            We finished by talking about the benefits of drainage and increasing the number of workable days, particularity in the spring.

Philip:                          It's an absolute fact that if the field returns to field capacity after heavy rain quicker then you're not long before you can get back onto the soil without doing as much significant damage, and as a direct result of that you will have more workable days. In a spring situation, because you are already wet, you are waiting for it to dry, you are going to get much more benefit in spring and if we’re trying to help to control grass weeds by putting more spring crops in the rotation, this is going to become more significant – that’s really quite important. Immediately because the drains work well, your soil is immediately, or more or less, at field capacity. If you’ve got poor drainage through winter, you’re field’s probably water-logged. There's a big difference - you have got from water-logged to field capacity half the floor space has got to be empty.

                                    If you've got some good floor space, 50 percent floor space, then immediately you've got 25 percent of air in your field because of good drainage, whereas if you are waterlogged you've got none. It's going to take an awful lot longer to get to a situation where you don't do damage. You probably get on to it unwittingly quicker because the surface dries first and you think, "Well, I'm not going to do too much damage here," because of the surface, but at depth, that's really where it's critical. That is where you get still very high risk of damage. That, unfortunately, is the most expensive to put right because it is deepest.

Dr. Blackgrass:            Thanks a lot Philip. There is more information about drainage on the Black Grass Task Force website.

                                    After good conditions at the start of harvest the weather has now got a lot more catchy and things are quite stop start.  According to the most recent ADAS report across the whole of the UK around 40% of the winter wheat area has been brought in, although most of this is concentrated in the south and east of the country.  In other areas much less progress has been made.  This delay in the winter wheat harvest means that people following wheat with wheat will have a little less time to use cultivations and glyphosate to get on top of blackgrass.  Crop quality is reported to be reasonable to good.

Philip:                          This is the last episode of Dr. Blackgrass on air and I hope you've enjoyed listening and picked up some tips about black grass control. We would really like to know what you think about the podcast, good and bad. There is a short survey on the podcast page of the Bayer website for you to fill in. It should only take a couple of minutes to complete. If enough of you like the podcast, I expect we’ll be back later this year or in 2016. In any case, you can stay in touch by following and tweeting @DrBlackgrass. I hope drilling, pre-em, and post-em all go to plan. Goodbye.

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