NIAB - National Institute of Agricultural Botany

Orson's Oracle

The end game?

Posted on 16/05/2012 by Jim Orson

It's the time of year when the success or otherwise of black-grass control in winter cereals is judged. Reports from farmers suggest that it is a mixed bag and there have been some spectacular failures of control. 

This has been due to a combination of herbicide resistance and dry soil conditions when the herbicides were applied. These dry soil conditions not only reduced the control achieved by the pre- and early post-emergence herbicides but also the early autumn applications of products such as Atlantis. Tractor ploughing

The NIAB TAG Updates issued to our Network members expressed concern that this might happen and suggested that the application of Atlantis, or its alternatives, was delayed until the soil around the roots of the weed was moist. However, in many cases, the farmer’s desire to ‘get on’ proved too strong a temptation.

After the dry autumns of 2009 and 2011 it should be clear to all that there is a real issue about controlling black-grass in conditions that are hostile to good herbicide activity. Conditions for activity were not that important when the weed was more susceptible to herbicides but now they are critical. Just 'getting on’ and treating regardless of the conditions is not an option.

I suppose that the really nasty conditions for residual herbicides are those where there is sufficient moisture for crops and the weed to establish but the surface layer of the soil is too dry for good herbicide activity - exactly what occurred last autumn. During the most vulnerable weed stages to the pre- and early post-emergence herbicides, the soil surface layer was too dry.

The only real answer to this is to lower the background black-grass populations to a level where less is required of herbicides.

The implications of this are clear: increased levels of cultural control are required and everyone knows the options. Their adoption has to be discussed on a farm-by-farm basis.

What was surprising about last autumn, and previous dry autumns, is that there was still a benefit in terms of black-grass numbers in the crop from delayed drilling. This has not been closely researched but indicates yet again that black-grass seed does not have to emerge for it to be lost. 

Those who claim great benefits from ‘stale seedbeds’ should note that there are other significant mechanisms that cause seed loss. It is not just about getting the weed to emerge.

However, experience shows that delayed autumn drilling is a chancy option unless strategically adopted. In dry autumns, delaying the last couple of days’ drilling until the five day forecast is confidently predicting a good rain is an option for the worst affected fields. Hopefully, these fields can then be sprayed when the soil surface is moist. A few farmers tried this approach last autumn and it seemed to work.

A cultural measure not often featured as an option is to kill the black-grass in the standing crop or to ensile it before it becomes viable. This is most attractive when there are discrete patches of high infestations of the weed. These patches are often comprised of the most resistant weeds in the field.

So, there are both short and long-term considerations when assessing black-grass populations over the next week or so. The short-term issue is the implication of patches of black-grass seeding this summer. The long-term one is whether there is a need to reduce background black-grass populations to a level which is appropriate to the levels of control that can now be achieved by herbicides.

We are not at the end-game for herbicide control but we are at the end-game for the attitude that we can achieve high levels of black-grass control every year and that we can treat the weed at a time convenient to us. The weed has been slowly taking charge for the last three decades and everyone needs to recognise this.

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Buffer zones - getting the right balance

Posted on 09/05/2012 by Jim Orson

On the face of it, the efforts and the sacrifices made by the UK agricultural industry have been successful in terms of keeping pesticides out of water bodies (typically lakes and rivers). The most recent survey suggests that 99% of water bodies have pesticide levels below the Environmental Quality Standards (EQSs) established as a result of the Water Framework Directive.

However, the cost has been high. It includes some key pesticides that have failed to get registration in the UK because they may impact on the water environment. The most notable casualty has been isoproturon. This was not withdrawn because it was being recorded in water. It was withdrawn because it was estimated that it could occur in water at levels that could impact on the water environment at the 1,500 g/ha dose cited in the application for approval. Who knows; at a dose of 1,000 g/ha it might have been approved. Unfortunately, there are other examples of revocations of approvals or authorisations mainly because of the potential impact on the water environment.

But behind the headline of the vast majority of water bodies meeting the chemical standards for pesticides lie more threats to pesticides and their use. Typically, the standards set for drinking water are more stringent than the EQSs. This means that higher standards are required in those areas where drinking water is sourced. However, in the case of metaldehyde and clopryalid, which cannot be removed by current water treatment, it is necessary to meet the drinking water standard in untreated water.

All this means that those who farm in areas where drinking water is sourced will have to make greater efforts to keep pesticides out of water. This may not necessarily mean a two speed agriculture but it could potentially mean the two speed adoption of measures to meet the different standards.

It does not stop there. The interim arrangements for wider aquatic buffer zones are a reflection of increased concern in the UK over spray drift causing short term shocks to the aquatic environment. In this case, thresholds can be exceeded for only a short time but sufficiently long enough to cause damage.

The interim arrangements have been applied whilst there is a full scale evaluation of the issues. There is little doubt that some of the drift data used by regulators in the past do not now reflect the drift from wider sprayers travelling at 12-14 km/hour. Hence, there could be a more general requirement of 20 metre buffer zones for existing as well as new pesticides. I have already heard from one pesticide manufacturer who considers that a new active will have a 20 metre buffer zone and, as a consequence, is questioning whether to bring it to market.

This is an area that really worries me. Are we getting the balance between food production and environmental concerns right?

In this particular case, what bothers me is that the regulators may be trying to protect aquatic environments that, in reality, do not exist. Do most field side ditches have water in them long enough so that many of the organisms that regulators are trying to protect can flourish or even exist?

The French have adopted a system where they only buffer larger streams and water courses rather than every field side ditch. To me, this sounds more realistic. I know that this can lead to issues of what is a water course. The French have resolved this problem by saying that only streams that appear on a certain scale of map need to be buffered.

There needs to be an intensification of the debate on priorities for the countryside. We need to determine what we are trying to protect. It comes down to the old argument that food production, by definition, is environmentally harmful. Trying to establish unrealistic environmental standards will inevitably mean that UK food production will be reduced. It might be argued that additional environmental harm may be caused by asking others to meet this shortfall. We need a more balanced debate.

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Return of the rain

Posted on 02/05/2012 by Jim Orson

Right up to 28 April (last Saturday) the rainfall in Cambridge was below the monthly average. Then over Saturday and Sunday we had nearly 25 mm of rain. This means that at last we’ve had a month where rain has exceeded the monthly average.Raining

Much to the surprise of my wife, I decided to play golf on Sunday afternoon. The course was quite busy because the wind and the temperature were very acceptable. Underfoot the soil wasn’t soggy, because the course is built on shallow chalk.

I was playing a doctor who expressed surprise on how well the course walked. This led to a discussion on rain, soil moisture deficit and transpiration. At first, he couldn’t understand why it is most unlikely that summer rainfall will not recharge the watertables. I explained that in the summer the transpiration losses can be around 25 mm a week, and so it needs rainfall consistently above that figure to get water moving down the profile.

There has been sufficient rainfall locally for some drains to start running and, of course, tramlines are very wet. This can mean only one thing - pesticides in watercourses. In the West Midlands, where there was more rain earlier in the month, pesticides are appearing in feeder streams to reservoirs at levels above those specified in the good old Drinking Water Directive.

The usual suspects for this time of year are being recorded; clopyralid and the hormone herbicides mecoprop and MCPA. Fortunately, water companies are prepared to treat raw water in order to reduce pesticides in tap water to below the levels specified in the legislation.

These herbicides currently appearing in water are not effectively taken out of water by activated charcoal filters. This is because they are relatively water soluble and activated carbon is more effective on the more water insoluble herbicides, the classic one being isoproturon. But, the hormone herbicides are more effectively removed by the other process adopted to reduce pesticides in water - passing ozone through the water which oxidises chemicals in the water and breaks them down.

Unfortunately, clopyralid is one of two major pesticides detected in water that can get through both processes relatively unscathed. Metaldehyde is the other one. As they cannot be removed from water, their levels have to be reduced in raw water to below the threshold specified in the Drinking Water Directive. At the doses commonly used, this presents a particular challenge to metaldehyde, hence the importance of the Pelletwise campaign.

The problem is that all herbicides can occur in water at very high levels for a short time after a significant rain, particularly if the soil is already wet and the water treatment works cannot cope with these spikes of concentrations. This is where grass buffer zones to reduce immediate run off of surface water, particularly from tramlines, are particularly useful.

There is a great fear that the Water Framework Directive, which includes the Drinking Water Directive, will eventually result in the withdrawal of some key herbicides. Many now consider that these fears are over-egged. The Water Framework Directive says that the position of pesticides in water should not get worse, with the implication that an indication of the situation getting worse would be water companies installing additional facilities to remove pesticides.Winter cereal spraying

So the future may not be so bleak, provided that each and every farmer adopts sensible practice, both for filling and cleaning out sprayers as well as for the spraying operation itself. Identifying fields with a high risk of run-off and only spraying them when the risk is low is also an essential step.

Buffering watercourses with sufficiently wide grass strips is required in most cases. These strips are only as good as the weakest point and so they shouldn’t have breaks in them. Most breaks are where vehicles enter the field, but check to see if they are sufficiently wide and robust by walking them during periods of heavy rain to see if there is a breach from run-off.

The weather over the last few years has shown that we can get periods of very wet and very dry weather. Should this type of variable weather become even more exaggerated then there is the prospect that water companies may not be able to cope with pesticides in water with their current facilities. This really could spell trouble unless the farming industry reacts promptly to the situation.

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Pesticide resistance? Darwin rules OK

Posted on 23/04/2012 by Jim Orson

There was a time when considerable effort was spent trying to convince independent advisers and researchers that low doses cause pesticide resistance. There wasn’t much scientific rigour in the argument; apparently target organisms ‘got used to’ low doses and that was the start of resistance development.

That argument never struck a cord with me. My first experience of resistance was with powdery mildew to Bayleton (triadimefon), in the late 1970s/early 1980s after only a few years of use. We knew from trials that a quarter dose initially controlled the disease in the field, and most growers Charles Darwinat the time were using doses well above this. So, resistance wasn’t a result of incomplete control.

The science on the causes of resistance has been transformed by biotechnology. Typically, target site resistance is caused by genetic mutations that block the activity of pesticides at the single site of action. Enhanced metabolism is often caused by the over-expression (hyperactivity) of gene(s) that in susceptible target organisms would only result in the slow breakdown of the pesticide.

This suggests that typically it is high selection pressure (high doses, particularly if regularly repeated) that leads to the most rapid increase in resistance, as only the most resistant target organisms will survive a high dose. Provided these survivors have roughly the same fitness as the susceptible organisms to compete and multiply then they will slowly dominate the population - following the principles of evolution, first described by Charles Darwin.

[You will have noticed that I’ve extensively used the word ‘typically’ so far in this blog. This is because over the years I have learnt that whilst simple principles apply in the vast majority of occurrences of resistance, there may be some exceptions...]

So far, so good.Resistant blackgrass

Then recently I read some scientific papers suggesting that low, rather than high, doses were causing resistance to weeds in Australia. My first thought was ‘how dare these colonials challenge our cherished Darwin’ - so when I visited earlier this year I disputed their conclusions.

It was easily resolved - the argument was that low doses led to higher numbers of weeds that had a level of resistance. However, there was an acceptance that high doses may result in a more rapid increase in resistance, so it became an argument about populations and the resistance development rate.

In the UK we have experience of statements saying that less effective treatment caused more resistance. It is said that it was the spring application of ‘fops’ and ‘dims’ that caused more resistance in black-grass than autumn applications.

Autumn applications typically (that word again) gave more effective control and so only the most resistant black-grass survived. This would, as a consequence, lead to a more rapid increase in resistance. Despite resistance increasing more slowly as a result of spring applications, after several years it may still have increased to the same maximum level as that from winter applications. However, being the less effective timing also meant that there would be a lot more black-grass plants present - hence the assertion that the spring timing caused more resistance that the autumn timing.

In practical agriculture the rate of development of resistance and populations is perhaps a rather pedantic argument. Nobody intentionally uses doses that will provide inadequate control. If lower than recommended doses are used, which is rare for black-grass, they should be at an appropriate dose to provide sufficient control in both the current and future crops.

Hence, Darwin still rules OK! However, there are apparently many in the US Republican Party who still disagree!

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Technology with a future

Posted on 15/04/2012 by Jim Orson

On Easter Sunday we sang the hymn ‘Now the green blade riseth from the buried grain’. My mind wandered away from the service and to how fortunate we are in the UK to have both the weather and the soils that can sustain good crops of grain. Of course the hymn book, from an agricultural point of view, gets really revved up for harvest festival. There are hymns that convey the labour and planning that lie behind producing a crop and the age-old worry about the weather. ‘Hopes of sun and rain’ is from a hymn written by John Arlott, who is more remembered for Test Match Special (if you are old enough) than for anything else.

When you look at an atlas (or on Google Earth!) it is surprising to see that we farm at a more northern latitude than the Canadian prairies - noted for vicious winters and hot summers. Yet we have relatively mild winters and summers. So why are we so successful at growing wheat?Growing wheat

The explanation is clear; we have a maritime climate warmed by the Gulf Stream. In fact, look at the countries with the highest wheat yields - they are all islands that benefit from the moderating effects of the surrounding seas.

The Republic of Ireland has the highest average wheat yields in the world, followed by New Zealand; I believe the UK is in third place. New Zealand is capable of extraordinarily high yields, but these can often be achieved only with irrigation at the end of the season.

The reason for this very high yield potential is that, despite having the same number of days during grain fill (flowering to maximum yield at around 35% moisture content) as the UK, NZ accumulates yield at a rate about a third higher than ours.

My calculations suggest that, on average, the UK accumulates wheat yields at a rate of 0.23 t/ha a day during grain fill whilst in New Zealand the rate is 0.30 t/ha. This is because the Canterbury Plain is on the same latitude south as the very south of France is north. So, despite having the same temperatures as East Anglia during grain fill, their solar radiation is much higher.

It’s not only the weather but our soils that have in the past provided us with such a great advantage. They are relatively young and have not been leached of nutrients as have the very old soils in some other parts of the world. This meant that during the development of agriculture, when there was little or no knowledge of plant nutrition, we had a natural advantage.

Of course it is important that we exploit our natural advantages. Pesticides and plant nutrients have enabled us to tap much of that potential. But, we now seem to have reached the point where any further yield increases are incredibly hard to achieve. Not only that but some of the technologies that enabled us to exploit these natural advantages are under pressure because of pesticide resistance and/or from regulation.

What we need is more technology, and not less, if we are to play the role in food production that society now increasingly recognises as essential.

There are still those who argue that we should have less technology and we should return to more ‘natural’ methods. I cannot agree with this and that's why I was a bit upset by a recent letter to Farmer’s Weekly regarding the GM wheat trial at Rothamsted Research. The letter questioned why a milling spring wTrojan Room Coffee Potheat, a relatively minor crop in the UK, was being used, and that no-one would use the flour produced.

The letter is missing the point. Rothamsted Research is a scientific institution and this is an experiment into what may, or may not, be possible. To stop science’s quest for knowledge on such arguments is an attempt to stop the clock. It goes to show the lack of coherence in the objections to GM. Surely, even if you are against multinationals allegedly taking the easy options, such as herbicide tolerance, to make profits from GM, why object to a scientific study of the possibilities it may offer?

It is widely acknowledged that we are still in the early stages of using biotech to improve crops and so today’s commercial products should not be used to damn the technology. I live in Cambridge, the birthplace of internet usage. It was in the University’s computer lab where a picture of a coffee pot, the Trojan Room Coffee Pot, could be accessed on all the VDUs to see if it was sufficiently full to make the foot journey to replenish cups/mugs worthwhile. That surely is a technology without a future.

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