NIAB - National Institute of Agricultural Botany

Orson's Oracle

Spray drift and pesticide legislation

Posted on 19/05/2017 by Jim Orson

A couple of blogs ago I discussed some of the issues around aquatic buffer zones. I promised to mention spray application in a future blog. Well, the future starts here.

One issue that spray specialists keep banging on about is boom height. Lifting the boom so that nozzle tips are 20 cm above the typical recommended height of 50 cm can double spray drift. Why is spray drift so sensitive to boom height?

Drift from all types of nozzles can be minimised by ensuring that the tips of the nozzles are as low as possible above the target to provide good spray coverage. This is 50 cm for 110 degree nozzles at a half metre spacing. In addition, spray pressures should not be above around 3 bar for conventional flat fan nozzles.

Data produced from experiments in the wind tunnel of the Silsoe Spray Application Unit emphasise the considerable influence on spray drift of the height of the tip of the nozzle. Increasing it by 20 cm (8 inches) can double the drift from a conventional standard flat fan nozzle and the increase from extended range/variable pressure flat fan nozzles is even greater. These latter nozzles produce higher levels of drift than conventional flat fan nozzles when operating at 3 bar.

Jim Orson blog 195

The question frequently posed is why such a small increase in the height of the tip of the nozzle can increase drift risk so dramatically? The answer is clearly demonstrated in the photograph taken at the Silsoe Spray Application Unit. This shows that drift largely emanates from a zone a distance below the nozzle.

The actual distances involved will depend on many variables, such as nozzle type and size, wind speed, forward speed and spray pressure. However, in simple terms, where the tips of the nozzles are 50 cm above the target and the zone where most of the drift originates is 20 cm above the target, then increasing the height of tip of the nozzle by 20 cm can more than double the size of this zone.

There is a simple explanation as to why drift largely emanates from spray fan nozzles at a distance from the tip of the nozzle: the spray liquid leaves the nozzle under pressure and at a high velocity and entrains (draws in) air as it travels.

The influences of both spray pressure and air entrainment fade as the spray droplets move away from the flat fan nozzle and eventually the droplets fall solely by gravity if the boom is far too high. By the time they get to just above the target, the droplets are moving slower and are the most vulnerable to drift. Smaller droplets lose their momentum more quickly and so not only is the ‘driftable zone’ wider for fine quality sprays from flat fan nozzles but also the smaller droplets are more ‘driftable’.

There are calls for CRD to adopt four star nozzles in order that aquatic buffer strips can be reduced in width. The current three star nozzles reduce drift by 75% compared to a standard 11003 nozzle working at 3 bar pressure. Some ‘smaller droplet’ air induction nozzles meet this target but often at slow forward speeds and pressures which may mean some compromises in efficacy. Even when working at 3 bar they have a few issues with efficacy e.g. small weeds with foliage applied herbicides and, anecdotally, on potato blight. One way of reducing spray drift by 90% or even 95% is to use even coarser nozzles but this will result in further compromises with efficacy because of poor spray retention on leaves and/or spray distribution, particularly on small targets and even, perhaps, on the soil surface.

There are ways in which such drift reduction is possible and which largely or completely retain efficacy but it may require a radical overhaul of the vast majority of sprayers currently on farms. Air assistance is one option. With conventional boom sprayers, achieving a 90% drift reduction and the good and uniform spray distribution necessary for some targets may mean a reduction in boom height. Some sprayer manufacturers now offer 25 cm nozzle spacings as an option aimed at drift control with the recommendation that the boom is operated 25 cm above the target. Boom suspension then needs to be very good with effective height sensors and probably some articulation.

There is a long way to go on the issue of aquatic buffer zones and spray application. This topic deserves to be higher up on the agenda of the future of farming in the UK.

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What do plants do at night?

Posted on 05/05/2017 by Jim Orson


Early March is the time for the Cambridge Science Festival. This is a great event and this year I attended 11 lectures over the fortnight. One was on how plants detect the time of the day and the season. It was fascinating but I do not think that I am sufficiently competent to report accurately the current scientific understanding.

Much of the research is done on the weed Arabidopsis thaliana (thale cress). It was the first plant to have its genome sequenced and is a popular tool for understanding the molecular biology of many plant traits, including flower development and light sensing. The lecturer showed a time graph of the growth of Arabidopsis and, to my complete surprise, it only grew in the dark.

I discussed this with my wife and she came to the conclusion that there are similarities between Arabidopsis and me. We both respire all the time but can do only one other task. In the case of the plant it is to photosynthesise during daylight hours and to grow at night.

After reading a few papers it seems that many broad-leaved plants largely or only grow at nights, something that both Charles Darwin and I have noted! The opposite may be mainly true for cereals and many grasses. I have to highlight that this is a complicated issue and there are no absolutes and, also, much depends on issues such as moisture supply and ambient temperatures.

I think we have to be careful about what is meant by growth. It is, in the context of this blog, an increase in the physical size of the plant. However, it should be noted that growth starts with cell division at the shoot apex and ends with a change in the physical size of the plant.

The explanation for why warm nights are good for growth may be because they enable more plant respiration which provides the materials required for this process. However, the more I thought about the subject the more uncomfortable I became with the claim by some crop physiologists that warm nights during grain-fill of wheat encourage too much respiration of the plant’s reserves and therefore lower yields. I have unthinkingly repeated this statement in previous blogs, hence my decision to investigate further.

It seems the opposite is true and that warmer nights can encourage a faster rate of grain-fill. However, and it is a big however, in field experiments on both wheat and barley, the plots warmed only at night had lower yields because of reduced grain-fill i.e. smaller grains. This is because duration of grain-filling is determined principally by accumulated temperature (thermal time). In these experiments, any increase in the rate of grain-filling due to warmer nights was more than offset by the negative effects of the shorter grain-fill duration

I have tested this explanation with a few simplistic models of grain-filling and typical day and night temperatures experienced in the UK in June. I used an average daily maximum of 22 C and an average daily minimum of 10 C. Just raising the daily minimum to 11 C reduced the duration of grain-fill by between 3 and 7% according to which model I used. The possible increase in rate of grain-fill from the warmer nights quoted in the literature suggests that this will not compensate for its shorter duration.

However, real life situations are more complicated. The same daily average temperature, which drives the duration of grain-fill, can be achieved by two contrasting weather patterns; warm sunny days with cool nights or cooler cloudy days with warmer nights. Of these two contrasting conditions, warm sunny days with cooler nights will provide higher yields due to more solar radiation being intercepted by the crop because, if the average temperatures are the same, the duration of grain-fill will be unaffected. This is providing that the crop has sufficient moisture and nutrients.

Field experiments again where field plots are only heated at night, suggest that warmer nights between the third node stage and mid-anthesis of wheat and barley have more impact on final yield than during grain-fill. In this case the lower yields were due to a reduction in the number of grains at harvest. Again, the duration of this critical period of the crop’s development is largely driven by thermal time.

Please accept that this is a rather simplistic description of some very complicated plant processes.

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Where are the dead fish?

Posted on 21/04/2017 by Jim Orson

I recently attended a workshop on aquatic buffer zones. Some contributions indicated that they may not yet be sufficiently wide. There are two possible reasons for this. Firstly, it was suggested that spray drift could be far higher than that indicated by the models currently used in EU registration systems. Secondly, there were suggestions that higher levels of protection of aquatic ecosystems from pesticides may be necessary. I must admit that I was shaken by these statements because we already have aquatic buffer zones of up to 18 metres wide. The widest buffer zones are usually for insecticides but, rather ominously, one black-grass herbicide product (so far) also has an 18 metre buffer zone.

The obvious question was posed. Is there evidence that there is a problem from spray drift? More succinctly, where are the dead fish? Fish welfare is only one aspect of the health of aquatic ecosystems but the point is well made.

The Environment Agency publishes annually its analysis of the environmental health of the main water bodies in England. In 2015 only one of the 4,678 main water bodies in England contained a pesticide in current agricultural use at a level that was above the Environmental Quality Standard set by the Agency and others. The other nine water bodies failing to meet the Environmental Quality Standards for pesticides had active substances that have been withdrawn from agricultural or industrial use. Hence, on a grand scale there does not appear to be much of a problem from current agricultural use.

There are of course countless smaller water bodies and streams where environmental health is not regularly monitored and we do not know the extent of the impact of pesticide drift on their ecosystems. However, it has to be noted that the ecosystems, particularly of some smaller watercourses, are affected by other factors. Some ditches, particularly close to major roads, appear lifeless because of factors other than pesticides. Soil contamination and other pollutants have a major impact on many of our small watercourses.

Jim Orson NIAB TAG blog watercourse  Where do we go from here and how do we reduce unnecessary restrictions on agricultural productivity due to ever increasing aquatic buffer zones? Personally, I think that we need to start with the definition of a watercourse. The definition used by many authorities, including our Chemicals Regulation Division (CRD) of HSE, goes something along the lines of ‘a natural or artificial channel through which water flows’. Does this mean that we should really be trying to maintain the health of water ecosystems in ditches which are dry for most of the year? I am not so sure because as such ditches dry they contain a series of stagnant puddles which are not conducive to some of the aquatic organisms that the pesticide regulations are designed to protect.

It is interesting to note that the guidance document on protecting water ecosystems for the pesticide registration authorities of the EU member states uses a different definition of a watercourse. On page 40 it says that the guidance document ‘predominantly addresses the risk for organisms occurring in permanent edge-of field water bodies, that is, water bodies that contain water throughout the year’. That is, in my opinion, a more realistic definition of what should be protected.

In France only watercourses that are marked blue on a 1:25,000 scale map need to be protected by an aquatic buffer strip in order to avoid spray drift affecting aquatic ecosystems. I have found an UK government data site that has watercourses marked blue on a 1:10,000 scale. Using my experience of some farms, this site could be used to prioritise which farm ditches are worth protecting with aquatic buffer zones. Prioritising could offer the means of improving the protection of recognised watercourses on this map, not only from spray drift but also from other pollutants.

I offer this as a way forward but also would like to say that the ditches not appearing on this map may need some minimal level of protection, even when dry. This is particularly true of ditches at the bottom of slopes in drinking water catchments in order to reduce the risk of pesticides entering raw drinking water through run-off. However, as a general statement, not to spray within 18 metres of a puddly ditch is perhaps not the ideal way to address an overall improvement in water health.

It has long been argued that people are more likely to adopt improved practices if they can be provided with a hopeful vision. The vision on aquatic buffer zones as it stands is not that hopeful but prioritising watercourses may convince farmers that there is a practical and realistic way forward. It could be that prioritising the protection of recognised watercourses is also something that the UK government can still afford to support after Brexit by generously funding realistic sized permanent and floristic buffer zones which are easy to police. I mention the need for floristic buffer zones in order to support biodiversity too. Surrounding recognised water courses with such vegetation will provide the connectivity for biodiversity that many argue is necessary.

Of course, reducing spray drift will also help to lessen the area devoted to buffer strips. The concern is that methods of reducing drift beyond the 75% achieved by the small droplet flat-fan air induction nozzles may well mean poorer efficacy of many pesticide products. This issue will be the subject of another blog in the near future.

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Fake News, Fake Science and GM

Posted on 31/03/2017 by Jim Orson

I tend to be in despair over the quality of debate on new agricultural technology. This is because of the standards adopted by those who oppose such developments. In some ways it is comforting as it demonstrates that they cannot find facts that agree with their motives; all we get is fake news and fake science.

Take GMs. These are back in the news, partly because of the realism of the Princess Royal. She is a star in our family because of the immense amount of often unpublicised time she spends supporting the Save the Children Fund. My wife devotes much of her time to the charity and is very aware of the level of support it gets from Princess Anne.

Princess Anne’s comments on GM are in stark contrast to those of her brother, Prince Charles, who describes GM as “a gigantic experiment with nature” that will end with an ecological disaster. This statement does not give enough credit to nature where some of the processes used in GM occur naturally. For instance the sweet potato contains genes introduced, not by natural crossing, but by an agrobacterium. This fact does not seem to affect sweet potato sales at our local Waitrose.

The responses to Princess Anne’s comments were all too predictable, including the tired comment that GM creates ‘super weeds’ because some weed species have developed resistance to glyphosate. The green blob makes the fatuous and totally untrue assertion that this weed resistance has spread somehow from the GM herbicide tolerant crop. Ask any black-grass grower in England and they will be able to tell the green groups that you do not need GM crops to create ‘super weeds’.

However, there is some heartening news that attitudes to the negative stories on agricultural technology promulgated by the green blob are slowly changing. Some of the scare stories based on studies that they have funded and that are of contestable scientific quality are either not being mentioned by news organisations or are getting short shrift from them.

I was particularly heartened by a headline in The Times on 11th March which read “organic food is risk to the planet”. This was a comment on a Canadian review of the productivity and the environmental impact of organic and conventional farming. On a per tonne of output basis, there was no difference in environmental impact. The authors of the scientific paper did not say that organic food is a risk to the planet. 

That was the interpretation by the science editor of the paper. His argument is that because there is no difference in environmental impact per tonne of production, significantly less land is required to produce food conventionally. This will not only help in sparing the current wild lands but will also allow some of the currently cultivated land to be devoted specifically to biodiversity.

NIAB biodiversityIt could be argued that this conclusion may be questionable in the UK because our commodity food production is more reliant than most on inputs. However, it was comforting to read a paper in the Journal of Applied Ecology that also concludes that on a per tonne of output basis the environmental impact of conventional and organic winter cereals production in England is very similar. However, the fields surveyed in the study were in winter cereals only and so the biodiversity friendly grass/legume fertility building breaks in organic rotations were not taken into account. Hence, there is a need for conventional farmers to devote some land and management time to support biodiversity.

There are continuing and immense problems getting GM crops registered in the EU. As the recent leader of The Scotsman puts it “It seems that unscientific stance [on GMs] is a luxury the Scottish Government thinks we can afford at the moment, but it has to be wondered what that decision says about us as a nation.” What it is really saying is that while the current European political structures deride populism, their very own anti-GM stance is a prime example of anti-science populism.

Finally, I recently had a ‘did he say that’ moment. Did Tony Juniper, the well known green campaigner, really say on Radio 4 that he did not have a problem with GM resistant potatoes where the resistance genes were derived from wild relatives? (Listen here and fast forward to approximately 1 hour 50 minutes). I am pretty sure that he did. Now that is a step towards scientific enlightenment. Can we now remove the enormous fences and the security guards that protect the current GM trials in this country? I suspect that we all know the answer to that!

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The promoted narrative

Posted on 17/03/2017 by Jim Orson

A farmer recently mentioned the term ‘the promoted narrative’ over a stimulating lunch. I rather like that because arable agriculture is full of promoted narratives.

A dictionary definition of a narrative is ‘a spoken or written account of connected events; a story’. I think the word ‘story’ summarises some of the statements that I have heard or read in recent weeks.

For instance there is the commonly made statement that an early spring application of chlormequat or another plant growth regulator will stimulate tillering in late sown winter wheat. This is a story. True enough, chlormequat will increase the number of fertile tillers or heads of wheat at harvest. However, it does this by decreasing the tiller loss that occurs from about the first to second node stage rather than by increasing the number of tillers before those growth stages. Hence, application just before the first node stage is perfect for reducing tiller loss. It cannot possibly increase the number of potential tillers when applied in the early spring because only one tiller can emerge from a leaf axil and production of new leaves is a function of thermal time (day degrees) and this process is not modified by plant regulator application.

In terms of yield, the application of chlormequat just before the first node stage of winter wheat can be a good thing in years with a dry spring and a good grain fill. 2011 is a case in point. The wheat crops, untreated by chlormequat, shed too many tillers in May because of the drought. However, the rain in early June and good levels of solar radiation during grain fill meant that there was sufficient photosynthetic activity to feed the extra heads and/or grain sites in the chlormequat treated crops. In the absence of lodging, crop responses of up to 1t/ha were recorded in trials. Sadly the opposite was true in the following year. The dire wet and dull summer of 2012 meant that there was a low natural loss of tillers in May and there was insufficient photosynthesis to fill the grain sites of the untreated crops. Therefore the additional heads and/or grain sites that occurred as a result of chlormequat application were an additional burden. In the absence of lodging, losses from chlormequat application in that year approached the gains measured in 2011.

The early spring application of chlormequat and other plant growth regulators is also said to increase the rooting of late sown wheats. It may do, but independent trials have shown that any yield increase in late sown wheat from this timing is less than that from an application just before the first node stage. Come to think of it, has anyone found that late sown wheats are short of roots in the early spring? Wheat root production increases at an exponential rate during stem extension and so logically, an application of chlormequat just before this stage would be more appropriate. However, I think that any impact on roots from growth regulators is by the bye. I realise that this is a battleground between competing plant growth regulator products but it has never been identified in the field that plant growth regulators can increase nutrient and water capture from the soil.

Another promoted narrative regarding the spring management of late sown wheats is that they need more early nitrogen. They certainly need early nitrogen but they do not need more than a typical conventional crop. This is because the plants are small and while the root system is adequate it is not as developed as a typical conventional crop at this time and so, if anything, applying less nitrogen than for conventional crops is a wiser option.

I could go on about other promoted narratives. Okay…. one more; micronutrients. The story and the products keep changing. I wonder why. A few years ago the promoted narrative was that a single application of a mixture of micronutrients was necessary for all wheat crops, even those not showing symptoms. That was eventually blown out of the water by the superb AHDB project report on micronutrients for wheat. So the selling angle has now changed to a series of applications being required and/or that high yielding crops will only be achieved with their help. Do not fall for it. High yields are a result of healthy soils, good weather and good management. The latter includes using micronutrients only to treat visual deficiency symptoms or persistently occurring deficiencies that will cause symptoms later in the crop’s life. I was surprised by one aspect of the AHDB project: wheat showing a micronutrient deficiency symptom always responded visually to the relevant applied spray but yields were not always increased. This means that the approach I suggest is precautionary.

There are plenty of other promoted narratives; a common one is that organic agriculture is good for the environment. Yet another report has recently been published, this time from Canada, which concludes that this is not true when organic and conventional production is compared on a per tonne basis. Promoted narratives particularly abound for difficult to understand issues such as trying to define the dose of nitrogen required by a specific crop or the impact of weather conditions on yields. Simple values hide the huge variations that occur in real life. I could go on …… but I’ll leave it there!

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