Real Real Results

Last year, there was what I thought to be a pretty good advertising campaign by BASF (an agrochemical company), called BASF Real Results. This all started after a friend of mine started a little trial on his own farm to see if the top-of-the-range treatment recommended by BASF made him more money than his standard farm practice. It turned out that, in this trial, the BASF products did actually make sense to use, and so the campaign was born from the idea that real farmers could tell other real farmers what worked best for them, on their own farms with their own soil types. Nifty – and quite convincing.

This year, BASF have rolled out the idea to a wider audience, and asked for 50 new farmers to volunteer to be sent some free fungicides, and do the trials on their farm. I thought this sounded like a good idea as well, so investigated further. After a bit of digging I came to the conclusion that, no, actually I don’t think it does what it’s supposed to do. I didn’t want to take part. Here’s the problem.

The philosophy of these trials is that they are “real world”, which means they use big plots, or even just fields split in two. These get cut separately, and weighed, and the results are taken from that. Big areas like this have some advantages over small plots, chiefly that they can be relatively easily managed by farmers with farm scale equipment. Unfortunately, they have a serious flaw, which is that by taking such a small number of samples (normally two in this case), you are relying entirely on the underlying soil in the field to be exactly th same, so that the only factor which may cause the yield to change is the fungicide treatment that you’ve fiddled with. This, in my mind, is impossible. Take a look at these yield maps from our combine:

These maps are relative yield maps, so the darker the shade of green, the higher the yield

These are relative yield maps, so the darker the shade of green, the higher the yield

This is a fairly extreme example, but it makes the point. If you took the 2012 yield maps as being what the field was like, the western half is obviously better. If you only looked at 2013 you would say it’s clearly the eastern half which is best. If I was running a split field trial on this field in 2017, and one side yielded more than the other, how would I know if that was due to the fungicides, or to something else unknown? The simple answer is that there is no way of knowing this, and the only way to get around the problem is by taking a larger number of samples from around the field, and averaging them out. This is the way trials are run professionally, and for good reason. The more samples you have, the more accurate your results will be, from a statistical point of view.

Now, I hear BASF and ADAS cry, we have thought of that. Indeed they have, because there’s a great idea called Agronōmics which is designed to get around this. Remember the 50 farms that have been selected to take part in the Real Results trial? This is where the sample number comes from; each farm may or may not get an accurate result, but bundle all 50 together, and average them out, and then you get something with statistical value. I don’t have any problem with this, in fact it’s a great idea. But it does make a mockery of the supposed idea of the trial, which is that farmers get a real idea of what works on their farm. If you are one part of a large sample set, you’ll never know if you are the outlier, or a good data point. That’s why I didn’t (selfishly) want to waste my time doing it.

But I did still want to know what works here, so together with BASF and The Farming Forum, we have devised a more detailed experiment, which I feel a bit more comfortable in conducting with the aim of having usable results for myself. It doesn’t just include BASF, we also have trials with Syngenta, Bayer, and an untreated plot. It doesn’t just use the combine yield monitor, we also have a plot combine coming to take multiple samples. It doesn’t just take place on one field with one variety, there are two locations, with two varieties. It doesn’t just mean me getting one set of freebies, it also…well, you get the picture.

The basic outline is the same as the other 50 farmers, we use farm standard sprays at T0 and T3 (that’s the first and last fungicide applications), but for T1 and T2 we will be putting on farm standard, BASF, Bayer, Syngenta & nothing at all. There are three replications of each treatment, except for the untreated, which only has one for fun. the plots are 30x100m in size, and the trials look something like this:

HC 2

We have two fields in the trial:

HC 2

Soil type: chalky sandy loam – probably the least productive field on the farm

Variety: KWS Crispin – very good intrinsic disease resistance

Yield potential: 7-9t/ha

Farm standard T1 treatment: 0.8l/ha Keystone, 1l/ha CTL, 1l/ha CCC, 0.165l/ha Scitec, 7.5kg/ha Bittersaltz

Stocks 3

Soil type: chalky clay loam – in the top third of of fields for average yield

Variety: Reflection – poor natural disease resistance, but our best yielder in 2016

Yield potential: 9-11t/ha

Farm standard T1 treatment: 1.25l/ha Adexar, 1l/ha CTL, 1l/ha CCC, 0.2l/ha Moddus

On both of these fields, the farm standard fungicides will be substituted for the following,

BASF: 1l/ha Adexar, 1l/ha CTL

Bayer: 1l/ha Aviator 235 Xpro, 1l/ha CTL

Syngenta: 0.8l/ha Seguris, 1l/ha CTL

I’m quite looking forward to taking these all to yield, as I really believe it could effect our thinking for the future, especially as we have the mix of good fields, bad fields, good (disease resistance) varieties, and less good ones. And hopefully, because of how it’s designed, it really will be Real Real Results.

CS vs 750a – The Grand Finale

The end is almost nigh. On October 20th 2015 we found ourselves with a Cross Slot and a John Deere 750a in the same field, at the same time, drilling the same crop at the same seed rate. What better start for a test that had been much debated amongst all the saddo internet farmers (myself included).

A rare sight

A rare sight

Over the following months I published updates on plant counts, tiller counts, and then finally ear counts. In the middle were some stitched drone maps, and visual analyses. In case you missed them all, here’s a comprehensive list.

Day 408 – Cross Slot vs 750a

CS vs 750a Xmas update

CS vs 750a new year update

CS vs 750a early spring update

Cross Slot vs 750a super spring special

750a vs CS May data

CS vs 750a June Update

CS vs 750a: The Penultimate Post?

Anyway…harvest is almost done here now, we are just waiting for the spring beans and spring linseed to be ready. All the wheat is done, it was a rather disappointing year, with an average yield of 9.1t/ha, slightly below our long term average. The two fields which looked worst all year, both growing Reflection wheat, actually ended up yielding the best. One of them was this field, with a final result of 10.41t/ha. Incidentally, the other field, drilled three weeks earlier, yielded 10.73t/ha.

The Boring Bit

Of course, it would have been stupid to go to all this trouble, and then not get an accurate yield from the different drill areas. So that ruled out using our combine, and our kind neighbours at KWS came to the rescue with a plot combine.

It meant making a bit of a mess of the field with wheelings all over the place, but we ended up with a set of plots at both ends of the field ready to be cut with a small combine

It meant making a bit of a mess of the field with wheelings all over the place, but we ended up with a set of plots at both ends of the field ready to be cut with a small combine. It is possible to see the 750a plot which is a different colour to the CS and CO8 areas

What we decided to do, after consultation with the trials experts, was cut six strips for each drill, at each end of the field. We took three each from the boundary of each drill’s plot, so we could compare them directly with a different drill only a couple of meters away. I think it’s easier to make a picture actually:

The blue area is the CS, the red 750a. I have put an X everywhere we cut a plot. This picture is is not to scale, it's just give an idea of what I'm talking about.

The blue area is the CS, the red 750a. I have put an X everywhere we cut a plot. This picture is is not to scale, it’s just give an idea of what I’m talking about.

Obviously we did not cut any tramlines, and all the plots were either 10 or 12m long, and 1.5m wide. The same method was used on both the light and heavy end of the field, giving us 12 plots per drill, and 36 in total. I did end up moving the heavy plots up the field by around 100m to get out of the black grass, which could have affected the data. The combine measures weight, moisture and bushel weight. All yields were corrected to 15% moisture.

FullSizeRender 60

The Interesting Bit

We all know from watching Who Wants To Be A Millionaire that the wisdom of crowds is infallible. So when I made a Twitter poll to see what people thought the results were going to be in this experiment, I was not surprised at what came out of it:

Screen Shot 2016-08-20 at 14.54.28

But the crowd is wrong. Because yes, that deafening sound you can hear really is the STATISTICALLY SIGNIFICANT RESULT klaxon. Let’s cut to the chase, so everyone who doesn’t want to read on can go home:

The 750a produced statistically significantly higher yields than the other two drills

At the end of this post I will put an appendix with all the data, so anyone who has too much time (I’m looking at you Sills) can do whatever they want with it. For now though, here is a summary.

Screen Shot 2016-08-20 at 16.00.23

Clearly there is a big difference between what happened at the light end vs the heavy end of the field. Not surprisingly, there is no significant difference at the heavy end between the drills. At the light end it is a very different story, with the 750a yielding around 0.8t/ha more than the other two drills. If we talk about just the top end, the result is highly significant, with p<0.001. For those people like me who have forgotten their A level maths, this means that there is a less than one in a thousand chance of the results being from coincidence rather than an actual effect.

When we combine both the results from both the light and heavy parts of the field, we find the 750a has a yield benefit of 0.4t/ha. This is still statistically significant, with p=0.023, meaning there is roughly a one in forty chance the results are coincidental. [For reference, anything with a p value of less than 0.05 is considered to be statistically significant]. It is this result which leads me to the conclusion I wrote at the start of this section, which is that the 750a has produced significantly higher yields.

The other data that came out of the experiment was the bushel weight for each sample. In short, there is no correlation between drills or yields and bushel weights. Here’s a pretty scatter diagram. You’ll find a statistical analysis of drill vs bushel weight at the end.

Screen Shot 2016-08-20 at 16.36.46

What this all means

I think the first thing to point out is that these results are from one season, in one field, growing one variety on one (maybe two) soil types. What I’m saying is that they are by no means the definitive “answer”. However, I’m not aware of any other trial that put these two drills up against each other in a fully no-till situation. Certainly there is not one that has been done in UK conditions. So for now it is as good as we have got.

I do wonder what has actually caused the yield difference. For me it can only be one of two things. Firstly there is row width – which was significantly narrower on the 750a than the other two drills. Secondly there is establishment and plant populations. The 750a did much better on these numbers; I suspect they would be statistically significant, but the analysis hasn’t been done yet. I think though that once a seed is in the ground at the correct depth, and has germinated, any effect from the drill is finished. On that criteria, the 750a has clearly performed the best.

Where does that leave the Cross Slot? As I outlined in the first blog post, it is much more expensive to buy than a 750a, at around 2.5-3x the price per meter of drill – for much wider row spacing. If you felt that this was a problem then it is possible to go closer, but it will cost even more and take more pulling. The running costs also seem to be much higher as well. All of this pales into insignificance if a higher yield can be achieved, but…

I do not believe for one second that in every year in every situation this result would be repeated. What I do believe to be more likely is that sometimes the 750a would win, sometimes a Cross Slot (although possibly the row spacings would need to be matched to even things up fully). That’s all nice, but I can’t see the point in paying a lot more money to not get a performance increase.

After the plot combine had visited

After the plot combine had visited

There are of course some USPs to a Cross Slot. They are very well built, and will no doubt last a long time. The ground I saw in NZ was amazing, with huge boulders not an uncommon sight. Our farm, though, is real boys land in comparison. Our current drill is 16 years old and still in great shape. A second USP is the very large, 50cm, range of vertical travel for the coulters. Again, great on the rough NZ pastures, but not something we need. As for the whole point of the Cross Slot opener, which puts the seed in a high humidity slot – I have no reason to doubt that it happens. But how often is a lack of moisture at establishment a problem for us? Very rarely in a no-till situation, even with a basic tine drill.

So all in all, on our farm, in our conditions, I personally do not see a need for these characteristics. In the absence of any evidence of a yield benefit, I couldn’t see wanting to buy a Cross Slot. This may well be different on someone else’s farm in the UK, I have no idea. But spending this amount of money without trying it first in your own conditions, is in my opinion totally nuts. You pays your money and you takes your choice…

And the John Deere? No doubt a good drill, it was clearly the best performing in this trial, from day one through to harvest. Is it any better than a Sumo, Weaving, or any of the others? I don’t know. What it does have going for it is a proven track record and strong residuals. I can’t help but feel it may be getting a bit left behind in technology though, as the design is basically unchanged in two decades. That could be a good or a bad thing depending on your preferences.

So there we have it. I still can’t quite believe we got a Significant result, I would not have ever predicted that. Not too bad for a farmer trial. But was it really a farmer trial? I had a lot of help: Ian for providing the Cross Slot, Huw at Ben Burgess for bringing the 750a. Christina and Robert at ProCam for spending hours counting plants, tillers and ears. John, Kim and Ed at KWS for organising the harvesting and yield measurement, and doing the stats. Thanks all.

Walston Out.

[PS Please do not use any of this blog or the data in it without asking first]


CSvs750a Raw Data

Stats Analysis

CS vs 750a: The Penultimate Post?

I’ve just had the data in for ear and grain counts. I have multiplied them up using an assumed TGW (thousand grain weight) of 45g. I’m going to go out on a limb and say they will not be very representative, although I hope very much to be proved wrong!

Screen Shot 2016-08-05 at 16.48.42

I think harvest will be in roughly 10 days. I have one concern at this point which is there has been a lot of spring germinated black grass at the bottom (heavy) end of the field. I am going to have to try and select a strip for cutting the trial plots that does not have any BG in it, because it is at levels that will affect the yield. I think this will be possible, but it will probably mean not cutting in exactly the same areas the the plant counts have been done in. Luckily there are no weeds at the other end of the field, so we should get on well there.

750a vs CS May data

Small problem this month, in that the person doing the plant counts on the heavy end had a GPS problem, and couldn’t find the stakes marking the count plots for the 750a and CO8. This month’s data from those plots is marked in yellow, and was taken from a similar area. The heavy land CS plot and all the light counts are in consistent locations.

Screen Shot 2016-06-01 at 13.46.35

Cross Slot vs 750a super spring special

Unfortunately spring hasn’t really sprung yet, but hopefully it will soon. Regardless, here is the latest tiller count data from the drill trial. Same old same old.

Screen Shot 2016-05-02 at 21.00.12

If you’ve read recent posts here you will know about the drone I’ve bought. It may have had a slight altercation with a tree, putting it out of action for the time being, but before that I made a map of the drill trial field. Here it is, along with some more photos taken the same day, but from a somewhat lower altitude. You can click on any of them to get larger versions.

Here is a large version of the whole field photo. Aside from the different drill areas, which will be explained in the next picture, you can see in the top left quadrant a zigzag darker line where we did not spray any Pacifica (a herbicide for killing grassweeds). Alo in the bottom left you can see the remains of some sort of Roman or bronze age settlement.

Here is a large version of the whole field photo. Aside from the different drill areas, which will be explained in the next picture, you can see a zigzag darker line running from half way up the left side to halfway along the top. This is where we did not spray any Pacifica (a herbicide for killing grassweeds). Also in the bottom left you can see the remains of some sort of Roman or bronze age settlement. A stream runs along the bottom, curved, headland and we normally get some flooding, which is what the brown patches are

I tried, and failed, to make some sort of clever overlay of this info on the previous image. The blue section is the Cross Slot area, the red is 750a. Everything else is CO8. The 750a area is very obviously different to the other two, which are indistinguishable. From this perspective the crop looks pretty ropey, so I went down to ground level and took the following photos, the locations of which are also marked on this image

I tried, and failed, to make some sort of clever interactive overlay of this info on the previous image. The blue section is the Cross Slot area, the red is 750a. Everything else is CO8. The CS and CO8 are indistinguishable, but the 750a area looks distinctly different. From this perspective the crop looks pretty ropey, so I went down to ground level and took the following photos, the locations of which are also marked on this image

1 - CO8. Looks much better from the ground!

1 – CO8. Looks much better from the ground!

2 - Cross Slot. Looks similar to CO8, not surprising given that all the numbers match up too

2 – Cross Slot. Looks similar to CO8, not surprising given that all the numbers match up too

3 - The Cross Slot / 750a seam. There was a little bit of overlap between the drills here, so the difference is not as apparent as I thought it would be

3 – The Cross Slot / 750a seam. Is it slightly lighter green than the Cross Slot? I wonder if that could be due to the same amount of nitrogen divided amongst a greater number of plants & tillers.

4 - 750a. Slightly less ground visible, but the difference seems much smaller down here compared to from the drone

4 – 750a. Slightly less ground visible, but the difference seems much smaller down here compared to from the drone

5 - 750a / CO8 seam. Not a very good comparison because of the coincidental tramline it landed in. Still - not a massive difference though

5 – 750a / CO8 seam. Not a very good comparison because of the coincidental tramline it landed in. Still – not a massive difference though. Again, 750a looks maybe a slightly lighter shade of green

So there we have it. Until next time.

Mythbusting MOP

One of my favourite programmes finished recently, and to honour it here’s a special blog post.

The myth

The most common way of getting potassium, which is one of the big three nutrients, onto arable crops is to use a product called MOP – alternatively know as muriate of potash, potassium chloride or KCl. It’s the most concentrated and cheapest way of buying potassium. In the soil health world that I occasionally inhabit, there is a strong feeling though that MOP is bad for the soil fauna, and the reason given is that it contains chlorine. I always used to subscribe to this theory, it just makes sense. I even argued with people since I was sure it was right – until my mind was changed. What I’m going to examine here is the validity of this claim, which is what gets trotted out all the time by means of justification:

MOP is bad for the soil because it contains chlorine, which is also used in swimming pools to keep them sterile

The chemistry

The technique of chlorination has been used now for over a century; the first town in the world to have all its water treated was Maidstone, in 1897. There are several ways of getting chlorine (Cl2) into water. You could bubble the gas through the water, but it isn’t very practical. In home swimming pools people often use something like stabilised chlorine (sodium dichloroisocyanurate), which works by slowly and constantly releasing small quantities of Cl2. Public swimming pools and water treatment plants tend to use something like sodium hypochlorite. Wherever we start, we produce the same important acid:

Cl2 + H2is in equilibrium with HCl + HOCl
NaOCL + H2is in equilibrium with Na+ + OH + HOCl

What this means is that we put chlorine gas (Cl2) into water (H2O) and out comes hypochlorous acid (HOCl), and the result is the same when using sodium hypochlorite. This reaction and its products should be familiar to everyone, not just those with swimming pools.

It’s bleach.

Obviously it is very diluted, but it’s this hypochlorous acid that kill all the bugs in chlorinated water.

Now let’s take a look at the MOP (or KCl to use the chemical formula), and what happens when we put that in water.

KCl + H2is in equilibrium with K+ Cl + H2O

What we have here is MOP being added to water, and forming potassium and chloride ions.

As is obvious, there is a fundamental difference here in what is in the water: one of them is bleach, the other is the same as when you dissolve normal table salt. The important thing to realise is that although they are written with the same two letters, “Cl”, chlorine gas is not the same thing as a chloride ion. And to take the point further, it is not a valid comparison to say putting chloride ions into the soil is the same as chlorinating a swimming pool, because the chemistry at work is totally different.

I think it’s safe to say that this myth is

The biology

But hold on!

So dissolving MOP in water is the same as dissolving salt (NaCl) in water? Don’t we all know salt kills bacteria, which is why we use it to preserve food? Yes, that is true, so let’s find out what sort of concentrations of Cl ions we are introducing to our fields when we put on MOP. I’m going to work this out as I go along, with no idea what the result is going to be.

1 hectare of soil, 10cm deep, will have a volume of

10,000 x 0.1 = 1,000m3

We are told that an ideal soil is 45% minerals, 5% soil organic matter, 25% air and 25% water. If that’s the case we have 250m3 of water, which weighs 250,000kg

We now add 100kg/ha of MOP. The molecular weights of K and Cl are 39 & 35 respectively, so of that 100kg we have

100*35/(39+35) = 47.2kg of Cl ions

that means our concentration of Cl ions is

47.2/250,000*100 = 0.019%

What does that mean???

A grain of salt weighs 0.000064799kg, of which 60% is chloride.

So to get the same concentration of Cl ions from one grain of salt (compared to 100kg/ha of MOP), we would need to add

0.00003887*100/0.019 = 0.2046kg of water.

Or to put it another way, 5 grains of salt in a litre of water. To me, that does not sound like it’s going to inhibit much microbial life, but let’s just check if that’s true. This paper shows a much more concentrated (11.68g of salt in a liter of water) solution actually increases the rate at which bacteria multiply. So what do I think about the myth of the Cl ions causing a problem by themselves?

The physics

There is one final MOP myth that I should look at whilst we’re on the subject. It’s that MOP actually affects the soil texture, making it less workable. One common refrain is this:

They used MOP to firm up clay subsoils when building runways during the war

I’ve spent quite a bit of time on Google, and can’t find that particular use mentioned anywhere aside from here, which is where I took the quote from. I’ve also tried looking for articles talking about MOP and soil hardening/texture etc, but only found this one article that mentions the idea. Here is the full paragraph in question. If you don’t want to bother reading the whole thing, it basically says it’s technically possible, but unlikely to actually happen:

The next claim has to do with the idea that K “makes the soil hard” and damages structure. As a monovalent cation, K can, if added in large quantities and given time, displace some of the other cations on soil exchange sites. If most of these exchange sites carried monovalent cations such as K or sodium (Na), soils would tend to “puddle” and be difficult to manage. The number of exchange sites is measured as the CEC, which range from single digits to the 40s or higher, depending on soil texture and organic matter. Each CEC unit occupied by K translates to 780 lb of K in the top 7 inches of soil. The great majority of exchange sites carry divalent cations such as calcium and magnesium, and this will continue to be the case even if we add hundreds (and in many soils thousands) of pounds of fertilizer K per acre.

Finally, I asked a friend (thanks James) to search the academic literature, but he couldn’t find any papers talking about this effect. So for this final MOP myth, I’m going to have to say there’s a bit of a lack of evidence one way or the other, and go for this verdict:

If anyone out there has more evidence on any of this, please do let me know.

The expert

As this isn’t my area of expertise (what is?) I thought it would be best to get the science checked out by someone cleverer than myself. What could be better than finding an academic from one of the top two universities in the country to give it the OK? No one from Hull was available, and since I live close to Cambridge it seemed like a good bet. So I must thank Dr Céline Merlet for her help in making sure my chemistry was good, and for also going out of her way to check my maths on the concentration calculations. It’s much appreciated.

Neonics, pyrethroids, rapeseed, guesses and dodgy stats

Standby for some unscientific science. Here’s a story about two fields of oilseed rape on our farm.

Field 1

Here’s the deets. 18ha field, sown with Campus OSR. Half of it was drilled with Hypro Duet seed dressing, which is a fungicide. The other half had Cruiser dressing, which is a neonicotinoid [neonic] insecticide – and it was drilled roughly a week later. As fans of Countryfile will know, neonic seed dressings are currently banned on oilseed rape…apart from some small parts of the country, one of which happens to be where we farm. Apart from the neonic dressed seeds, the field has had no other insecticides applied at all. Oh, and it had a companion crop of buckwheat, lentils & fenugreek.


Neonic on left, no insecticide on right

I went out last week to count how many flea beetle larvae there were living in the plants right now. I took 10 plants from each treatment, all samples were done within about a 30m circle. I then split open all the petioles where I could see a brown lesion, and counted the larvae. Sometimes I couldn’t find one when it definitely looked as if I should have; maybe I squashed them or was just blind. But hopefully my errors were consistent.

I found an average of 10.5 larvae/plant in the non-neonic area, compared to 8.6 in the treated. Experiments from AHDB showed that having 5 larvae/plant in the autumn did not have an effect on yield, but obviously both of my results are higher than that. On first glance it would appear the neonics have had a positive effect on keeping the flea beetle infestation down.

The neonic treated plants (left) are significantly smaller than the untreated (right)

The neonic treated plants (left) are significantly smaller than the untreated (right)

But unfortunately it was not as simple as that. The treated area was drilled around a week later, and with a higher seedrate. This meant that the plants were significantly smaller than in the untreated bit. So I walked out again and did a plant population count – 33 vs 58 plants/m2. Multiply this number by the larvae counts, and we see that there are actually more larvae in the neonic area – 345 vs 503 larvae/m2. And finally… I counted how many petioles each plant had, and then divided the larvae count by that number. The result was almost identical 1.18 vs 1.19 larvae/petiole.

So the neonic area “won” the first test, “lost” the second, and “drew” the third. What does it mean? I’ve no idea! As always, harvest will tell the only story that actually matters.

[UPDATE: Since writing this I was worrying about a couple of possibilities, so I have investigated them further. First of all, I wondered if perhaps I had taken the samples from too close; maybe some beetles had leaked over from the non-neonic side. So to test this I went over to the other side of the field, as far away as possible, and checked again. I did not do a full “scientific” sample set, but there were no fewer larvae than the first location.

Secondly I thought maybe the neonic seed treatment was irrelevant, and the higher infestation was down to just the lack of foliar sprays. Luckily I could test this too, as we have a third field that was drilled entirely with neonic seed, but had no insecticide sprays at all. Again I did an informal count and the numbers were much lower, maybe 4-5 per plant. So even with no sprays it is possible to be below the yield reduction threshold.]

Field 2

45ha field, all drilled at the same time with Picto and a companion crop of vetch, buckwheat and lentils. The seed dressing was Hypro Duet – i.e. not an insecticide.

Does it matter what is what? There's no visible difference

Does it matter what is what? There’s no visible difference. Although perhaps more interestingly the combine wheelings are fairly obvious

In September there was some flea beetle pressure, so we were given a recommendation to spray with a pyrethroid. Personally I was less than convinced, having done similar things last year – so we left 25% of the field un-sprayed. A month or so later we had another recommendation for pyrethroids again, this time for stem weevil. The whole field was treated.

I took all the same measurements as in the first field. There were more larvae in the once treated area compared to the bit sprayed twice – 3.6 vs 1.5. However, both are still below the threshold of yield reduction. Plant populations were odd; 81 vs 63/m2. It didn’t look different to the eye, but the stats never lie (errr…). This means we had more flea beetles in total in the once treated bit, 293 vs 94 larvae/m2. The plants were of pretty similar size, 7.6 vs 6.8 petioles/plant, which in turn means double the number of larvae/petiole in the once area.


I think drawing conclusions is easier here, as there’s a much closer and more scientific comparison. It seems clear that the first application of pyrethroids had some effect on reducing the number of flea beetles. That shouldn’t be surprising, but as the plants seem healthy and the larval numbers are below yield affecting thresholds I’m happy with the decision not to spray. In fact I only wish I had left some of that part of the field un-treated on the second application as well.

I think the difference between the two fields is interesting. The neonic treated field has a much higher burden of flea beetle larvae than the untreated one, but they are a few miles apart, using different varieties and different companion crops. The only certainly at this point is that neonics are most definitely not a guaranteed way to keep flea beetle at bay. I’ve been saying for a while now that if we grow rapeseed next year it will not be treated with neonics, even if they are permitted. I haven’t seen a reason to change that opinion yet.