NIAB - National Institute of Agricultural Botany

Orson's Oracle

Black-grass allelopathy nonsense?

Posted on 30/04/2015 by Jim Orson

Black-grassThere is an aspect of black-grass cultural control practice with which I would like to take issue. There is the notion that multiple applications of glyphosate are needed in the autumn to maximise the emergence of black-grass plants and hence maximise seed loss prior to sowing the following winter crop. This is based on the unsubstantiated theory that allelopathy is the cause of the observation that there is an apparent higher total emergence of black-grass when two or more applications of glyphosate are made to a false seedbed in order to kill newly emerged black-grass, rather than when a single application is made just before sowing the subsequent autumn sown crop. In my opinion there is a much more likely explanation for this than allelopathy being the cause. 

The Oxford Dictionary defines allelopathy as “the chemical inhibition of one plant (or other organism) by another, due to the release into the environment of substances acting as germination or growth inhibitors”. In this case it is suggested that exudates from the roots of newly emerged black-grass prevent the germination of neighbouring viable black-grass seeds in the soil. Hence, it is argued that allelopathy has to be avoided to ensure maximum germination of black-grass seed, thereby maximising seed losses before sowing the following winter crop. However, it should be noted that no root exudates that damage the germination or growth of black-grass or other species have ever been identified in black-grass but more proof is needed to discount the claim of allelopathy.

There are data in HGCA Project Report 381 ( on the impact of cultivations and dormancy on black-grass populations that indirectly suggest allelopathy is not the explanation as to why there is an apparent higher total emergence of black-grass when several applications of glyphosate, rather than a single application, are made to a false seedbed. There is no part of the report that covers this specific aspect and some work has to be done to extract the relevant data. Luckily for you, I have attempted to do this work! In this project there were two dates of drilling of winter wheat but for both drilling dates, no application of glyphosate was made after harvest until a single application just prior to sowing. Therefore, the difference in the number of black-grass counted at the time of glyphosate application indicates the increase in the size of black-grass population between the two drilling dates.

The first diagram shows on the horizontal axis the number of black-grass seedlings just before the single glyphosate application made prior to the first drilling date of winter wheat. You will note that there were three cultivation systems; cultivate immediately after harvest of the preceding winter wheat (in the project a Simba Solo was used), cultivate immediately before drilling (the glyphosate was applied immediately before the cultivation) and direct drilling. The vertical axis shows how much additional black-grass emerged prior to the delayed drilling, expressed as a proportion of the initial count. So a two on the vertical scale shows that there were double the number of plants emerged before a single application of glyphosate being made prior to the late drilling than the number emerged before a single application of glyphosate prior to the early drilling.

This first diagram agrees with the field observations that early emerged black-grass may impact on the establishment of later emerging black-grass. The higher the number (particularly over 50-100 plants/m2) of black-grass plants prior to the first drilling, the less the proportional increase in numbers prior to the second drilling. In most situations, at the higher infestations, the multiplication was one or below indicating that there was no increase in the number of plants between the two drilling dates. Those who promote the notion of allelopathy would say that this proves their point, with allelopathy being absent or low at the low populations and high at the high populations. Accepting this notion means accepting that there is an increase in the proportion of ungerminated seed as allelopathy increases, leading to an expectation of proportionally higher numbers emerging after the later sowing date where the background populations are high.

To test this expectation, I have prepared the second diagram. This has the same horizontal axis but the vertical axis is now the increase in the proportion of emerged black-grass plants in the late sown crop prior to Atlantis being applied at the 2-3 leaf stage (it worked when the project started) or in the untreated areas. This shows that the proportional increase appears to show the same pattern but the rate of reduction is less, most probably because the count was taken when the most advanced black-grass were only 2-3 leaves. There is no apparent association with supposed low levels of allelopathy at the low populations in diagram 1 resulting in lower levels of black-grass post-crop emergence, or supposed high levels of allelopathy at the highest populations maintaining more viable seed which would germinate in the following crop (diagram 2).

Hence, allelopathy appears not to be the explanation for the relationships between the background black-grass population of the site and the proportional increases in plant counts, either before late drilling or early post-emergence of the crop. The ‘shape’ of the diagrams strongly suggests that the far more logical explanation is intra-specific competition in black-grass (i.e. simply black-grass competing with other black-grass). This can take two forms. One is where the shading by the earlier emerged black-grass prevents light getting to the soil surface thus inhibiting germination. This would have a similar effect to allelopathy and so this very limited data suggests that the cause is much more likely simply to be that later emerging black-grass is out-competed by the earlier emerging black-grass. Accepting that this is the explanation means that the seed loss through germination in the soil is the same regardless of the numbers of glyphosate applications made.

This latter and more logical explanation suggests that there is no need (in terms of black-grass seed loss) for multiple applications of glyphosate and using only one application just prior to sowing will have the same impact on the numbers emerging in the crop. However, on a practical note, letting black-grass get very advanced means that drilling after the glyphosate application could be delayed.

Reducing the number of applications of glyphosate will save money and operational stress and reduce the risk of glyphosate resistance in black-grass. It is interesting to note that the first weed to develop glyphosate resistance in the world was rye-grass (Lolium rigidum) in Australia and in the first recorded cases, the resistance mutations made it weak and uncompetitive. Should this be the case with black-grass, then using intra-specific competition to kill the weaker plants in the stubbles may be an additional anti-resistance strategy.

I am the first to admit that these data do not totally disprove allelopathy in the field and I suggest that specific research is required. However, it seems to me that those who have counted a higher total black-grass emergence after multiple sprays of glyphosate rather than after a single spray just before drilling, have overlooked the simple and more logical explanation of plant competition reducing numbers once the black-grass grows beyond the early emergence stage.

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Roundup causing cancer?

Posted on 20/04/2015 by Jim Orson

In late March, the International Agency for Research on Cancer (IARC) announced that glyphosate would be added to its list of agents that are “probably carcinogenic to humans”. The IARC is an agency within the World Health Organization so the announcement has been widely reported. This news has delighted those who oppose GM technology and/or pesticides. There are many “we told you so” articles on their websites and in the popular press. 

Does glyphosate really cause cancer? I am no expert on this issue but have been looking at the comments made by UK scientists ( and also, I have read an excellent blog which carefully weighs up the evidence used by the IARC when coming to its preliminary conclusion ( Interestingly, the latter quotes a huge American study which shows that farm workers are less likely to get the cancer in question (non-Hodgkin lymphoma) than the general population.

The IARC admits that it is working from a very limited database of studies on the subject. This reminds me of the Daily Mail type of article where one quoted study suggests that there is evidence that a particular food type causes cancer and yet within a few weeks there is another study that concludes the opposite.  The following diagram really puts such studies into context. The blobs are the average result for an individual study but the inevitable error in each study often means that a blob on the right or left hand side of the vertical line may not be significantly different to the line. According to the blog to which I referred, this is the case for the few studies on glyphosate and non-Hodgkin lymphoma. 

There are two reasons for me potentially to panic over the IARC announcement. One is that I have handled glyphosate over the last forty years or so and also, if it is true, then there could be implications for the availability of the herbicide. However, I am not even concerned after reading the comments on the evidence.

It is worth mentioning that the IACR list of known carcinogens includes alcoholic beverages, emissions from coal fires, untreated or mildly treated mineral oils, outdoor air pollution, solar radiation, soot, wood dust and smoking tobacco. I suggest that it is worth paying more attention to our exposure to these than the so-called ‘probable’ risk from glyphosate but please remember that pesticides should always be handled with care.

After researching the issue, I am also a lot more reassured about my coffee addiction (see the diagram).  In fact, I was once so concerned about my intake that I asked my GP if it was possible to drink too much coffee. He thoughtfully put down his cup of coffee and said “I hope not”. The diagram is also a comfort to those, like me, who love a glass of wine. A couple of years ago I heard a talk by an eminent scientist at the University of East Anglia who concluded that a healthy diet could be based on red wine and chocolate. Now where are those Easter eggs I have to finish eating? For health reasons you understand.

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Breaking the yield barrier

Posted on 09/04/2015 by Jim Orson

Soon the agricultural magazines will be featuring farmers who are striving for higher wheat yields and even trying to break the UK or world record. This leads to a healthy debate and it is interesting to read the various approaches that they are adopting. For some it is better plant nutrition and for others it is improved soil management etc. However, I remain sceptical that these welcome initiatives will lead to a significant break in the plateau of wheat yields that we have been on for the last twenty years or so.

By the mid-1990s we had nearly all the technology that we have today. Admittedly, since that time, we have seen the introduction of the strobilurin and SDHI fungicides and the steady increase in yield potential of new varieties. However, these have not produced the increase in average yields that might have been expected. There has been much debate about why this has not occurred.

There is much talk about trying to grab back the world yield record from New Zealand. I do not think that is possible because NZ has more sunlight (solar radiation), despite similar temperatures, during their growing season (see diagram). However, their average yields are similar to ours because natural rainfall typically limits their yields more than in the UK. Southland at the bottom of the South Island in NZ has more rainfall than the other arable areas and that is where the world record yield was grown. Further north, in the Canterbury Plain, even higher yields have been achieved with irrigation towards the end of their season.  

The rapid increase in UK wheat yields in the last quarter of the 20th century was due to the exploitation of current technologies by the industry. In particular, improved pesticides increased field yields but they are now subject to growing levels of resistance and legislation. All in all, this provides an unstable background to the attempts to increase yields further.

It is clear to me that we need a new technology or at least a significant shift in current technologies in order to break out of the yield plateau. I have been looking around and my current favourite is close to home.

Today’s wheat varieties all stem back to a freakish cross that occurred around 10,000 years ago between emmer wheat (a relative of durum wheat) and a wild goat grass. This produced the hexaploid wheat that we know so well.  It has a huge genome when compared to other crops and also when compared to many animals. In fact the wheat genome is five times larger than that of a human being. This ensured that breeders had plenty to work on and increasing yield potential is still possible, even after many years of scientifically based crossing and selection.

It is critically important to remember that the genetic base for all wheat breeding goes back to that one freak cross. It is both logical and perhaps essential to repeat that freak cross with a range of parents in order to bring more genetic diversity into wheat. This is what is being researched at NIAB and the early evidence is that such an approach could lead to a very significant breakthrough in yield potential.

This was part of a display by NIAB at the Cambridge Science Festival (see script of the display board). Let us hope that this promise will be delivered into practice but it will not happen overnight. The display also included how light drives plant cells and also the identification of genetic markers for the genes that influence the flowering date of wheat. NIAB has a good record on communicating science to the public at the annual Cambridge Science Festival and the researchers who volunteer for the festival hope that they will inspire the next generation of plant breeders. 

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The carbon footprint of your diet

Posted on 30/03/2015 by Jim Orson

It is Cambridge Science Festival time again and so far I have been to five events, ranging from lectures to panel discussions to hands-on demonstrations. What has struck me is the enthusiasm and modesty of the very high calibre presenters and the open-mindedness of the audiences. 

For instance, in one panel discussion on sustainability, a contributor from a campaigning organisation criticised big business but some of the younger members of the audience argued that it was only through business that society will improve its record. It was done in the context of a genuine debate about the issues rather than the shouting matches that I regularly experience when such issues are ‘debated’.

I had a similar experience in a workshop on choosing food that is good for the planet through reducing the carbon footprint of personal diets. It was run by the charity Cambridge Carbon Footprint ( Within a few minutes a member of the audience said that to achieve this aim we should all eat organic food. I commented (with some trepidation) that the overwhelming evidence suggests that conventional food has a lower carbon footprint and then almost ducked to avoid a boisterous rebuttal. However, the audience remained calm and one of the two co-presenters said that her understanding was the same as mine. She added that there are issues regarding the carbon footprint of food consumption that perhaps conflict with some ideological agendas. As another example, she said that plastic shopping bags have a lower carbon footprint than paper shopping bags. This exchange suggested that it was going to be an ideologically free debate.  It turned out to be great.

The workshop tackled the issue of getting reliable data on which to base decisions. It is extremely difficult to estimate Greenhouse Gas (GHG) emissions and everyone present accepted that it is almost impossible to achieve accurate data. This is partly due to having to decide what is and what is not included in any calculation.

We were told that in the UK, the average annual GHG emissions per person is around 12 tonnes carbon dioxide equivalent (this take into account other greenhouse gas emissions, such as nitrous oxide). I could not find exactly the same figure in the literature, which generally says around 10 tonnes. The higher figure quoted at the workshop may also take into account the GHG associated with the production of the goods imported into the UK, including imported food.

We were also told that of this 12 tonnes, 2.9 tonnes were due to the production, processing, distribution and packaging of the food we eat. When this figure was broken down, 49% was due to production, 24% processing, 19% transport and 8% packaging. It is obvious that for each food purchased these proportions will vary hugely. In the debate it was highlighted that buying from a nearby supermarket may be more carbon efficient than driving to a farmers’ market and so it is difficult to establish absolute rules about where to shop.

It is also difficult to develop absolute rules on imported food because its long distance transport by boat may have a surprisingly low carbon footprint.

However, there was general agreement that buying in-season vegetables should typically result in a lower carbon footprint and that generally meat carries a high carbon cost. Sometimes meat can have a more moderate carbon footprint; for instance if it is from animals grazed on uplands where little additional feed inputs are used.

The really bad news is that cheese almost always has a high carbon footprint and so I will have to view my beloved Stilton in a new light.Stilton

In most of the discussion, I felt that I was a paragon of virtue despite my love of cheese. I grow a very high proportion of our vegetables in my second-hand unheated glasshouse and on my allotment (which I access on my wife’s bicycle). In addition, I now grow cover crops on the allotment which I hope will largely obviate the need to dig it. Can it get any better?

Well, perhaps not because then we touched on the subject of food waste. Again there is the issue of defining food waste as well as measuring it. It seems that some estimates include such items as potato peelings. In this case, the huge waste removing carrot fly damage to the parsnips I grow must, at least, slightly tarnish my halo. Perhaps I could reduce our carbon footprint further by using insecticides to control this pest.

More on the Cambridge Science Festival next time.


Picture: Stilton - High carbon footprint but delicious.


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What’s happening with GM?

Posted on 17/03/2015 by Jim Orson

I made a big mistake at the end of a recent blog when I mentioned that we could soon expect to cultivate GM glyphosate tolerant oilseed rape. This optimism chimed with recent reports stating that we could soon grow waves of GM crops now that the EU has signed a new law on the cultivation of them. This law enables member states to opt out of or ban authorised GM crops. This means that decisions to allow cultivation of authorised GMs will be taken by member states rather than seeking a seemingly impossible ideal to achieve pan-EU decisions to cultivate such crops.

The hope is that this will encourage the EU Commission to bring forward votes on applications for GM crop cultivation; some applications have been stuck in the system for more than a decade.

However, many applications for cultivation were withdrawn some time ago. These include applications to cultivate blight-resistant potatoes, GM high starch potatoes and glyphosate-tolerant beet. It appears that there is no glyphosate tolerant oilseed rape in the EU approval system. What remains in the system is Bt (insect resistant) and herbicide tolerant maize. Currently corn borers, the target for BT maize, have limited distribution in the UK. These insect pests damage the stems (see image) and cobs of maize and increase the risk of mycotoxins in the grain. Whilst there are no major weed control problems in UK maize production, the ability to use glyphosate may reduce overall growing costs and it will certainly ease the management of the crop. In addition, with sympathetic management, glyphosate tolerant maize may enable the introduction of some biodiversity into a crop that has currently very low levels. 

So what of the wave of new GM crops? It is arguable whether it is worth the companies going through the registration costs to get EU approval to cultivate GM crops if there are only a handful of countries in the EU minded to allow them to be sown. The regulations are unnecessarily complex, expensive and restrictive and I suppose we will have to wait and see what happens. In the meantime, we will slip further behind the rest of the world in producing food more efficiently whilst minimising environmental impact. 

Perhaps of equal concern is the queue of animal feed crops containing the more recently introduced GM developments awaiting approval for import into the EU. There is always a natural slow down in decision making when an EU commission approaches the end of its tenure and a new one starts up. However, there have been no such approvals in the last year. Recently, Juncker, the new president of the EU commission, has asked for a review of decision-making on GMOs which will further exacerbate the problem. Nobody yet knows the full repercussions of the review but an announcement to clarify its scope is expected over the next month or two. In the meantime, it is unlikely that new import approvals will be made. This means that the supply of imported maize and soya will become ever more restricted. 

It is hard to understand how such a situation has developed where emotion rather than facts and a mentality lacking in ambition and vision has blanketed the debate on agriculture in Europe. I realise that some lobby groups and individuals have benefited from their anti-GM and anti-pesticide stance but it clear to me that this is an indication of a wider malaise in Europe. I suppose in the end, the rest of the world will demonstrate what we are missing. In the meantime, Europe will increasingly have to rely on the rest of the world for its food supplies. Inevitably, this anti-science attitude will lead to higher food prices. This may not be so bad for European consumers but it could be devastating for those in the less developed parts of the world. But hey-ho, the debate on GM and pesticides in Europe has always been based on the “I’m alright, Jack” mentality.

european Corn Borer Damage

Picture by Cornell University 

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