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Cabbage Stem Flea Beetle Solutions

 

 

We have brought together the widest possible experience of leading researchers, advisers and growers in combatting the upsurge in CSFB across the country seen since the loss of neonicotinoid seed treatments. 


Whether it’s getting the crop away from adult beetle grazing in the autumn or minimising subsequent larval damage, our resource identifies the most promising ways to Battle the Beetle and ensure OSR remains a key part of your combinable crop rotation.

 

Battling the Beetle

Cabbage Stem Flea Beetle has become an enterprise-threatening problem with serious rotational consequences. Made worse by agrochemical withdrawals and increasingly resistant populations, it is spreading across the country with few signs of rapid resolution.

But it wasn’t so very long ago that many wheat growers were facing a remarkably similar challenge with black-grass.

Encouragingly, this weed no longer threatens the future of wheat-growing in some parts of the country like it once did.  True, the days of simple ‘out-of-the-can’ solutions are long gone and continued pressure is essential to keep on top of the problem. However, focused research and practical experience have shown that black-grass can be contained and managed.

In just the same way, dealing with CSFB will demand a combination of different varietal, rotational, agronomic and other strategies based firmly on understanding the problem.  While the science here is in its infancy, a number of approaches are showing considerable promise in ensuring OSR can maintain its undoubted rotational value for most.

These include varietal tolerance; crop avoidance and escape mechanisms; techniques for confusing or diverting the pest; biological control opportunities; and a range of other management options.

How genetic breeding research could help combat stem flea beetle in oilseed rape

Marked differences between OSR lines in both their attractiveness to adult flea beetle grazing and their ability to support larval development have been identified in a concerted John Innes Centre programme funded by AHDB, BBSRC and industry.

Since establishing the first captive population of the pest in 2014, Professor Steven Penfield, Dr Rachel Wells and their team have also gained valuable insights into what makes CSFB tick, elements of its life cycle that might usefully be interrupted and possible natural population control mechanisms.

“Knowing your enemy has to be the key to tackling flea beetle,” insists Dr Wells. “Yet, when we started looking into the problem it rapidly became apparent there was nowhere near enough science in anyone’s understanding of the pest. Most of what was ‘known’ about it in the literature was anecdotal.

“We also realised that massive variations across individual crops and the many factors influencing the scale and location of the adult and larval damage as well as significant interference from other pests like cabbage root fly and stem weevil meant field trials were most unlikely to give us the reliable genetic understanding we needed.

“So, we established a captive population in a controlled environment as the basis for our work. In addition to enabling us to measure the effects of specific levels of pest challenge on different oilseed rape lines, maintaining this has taught us a lot about what CSFB needs to survive and thrive.

“For instance, we know emerging young adults don’t survive well in hot, dry conditions. They need moisture and shelter while they mature. Equally, we are learning what conditions trigger egg-laying, maximise egg-hatch and contribute to the greatest larval success and most rapid generation turnover.”

The JIC team has also been able to characterise a parasitic wasp and, in collaboration with the University of Warwick, identify entomopathogenic fungi having significant effects on beetle populations.

Undoubtedly their most valuable work, though, has been in pinpointing the genetic variation essential for breeding resistance or tolerance into oilseed rape.

“We have assessed the diversity set of almost 100 Brassica napus lines forming the key Defra-sponsored Oilseed Rape Genetic Improvement Network (OREGIN) resource for their palatability in carefully controlled adult feeding trials,” explains Prof Penfield.

“Assessment of scanned leaf images shows the average degree of damage varying highly significantly from 2% to 20% across these lines (Figure 1).

“Regardless of adult grazing levels, we are also finding marked differences between the success of larval development across the same OSR lines,” he continues. “We measure this by placing a set number of eggs in the soil at the base of each plant isolated in its own chamber and maintained under precisely the same environmental conditions.

“Following the whole life cycle through, we’ve recorded a four-fold difference in the number of adults actually emerging among the lines tested. This indicates valuable variations in their ability to tolerate the larvae as well as their attractiveness to adults.

“Because the OREGIN lines have all been subject to high density DNA mapping, ordering a total of 225,000 markers, we are able to correlate the traits we see in both respects with specific areas of the OSR genome to provide a valuable resource for plant breeding.”

While varieties bred for tolerance to flea beetle using this resource will be a number of years away, the JIC work offers more immediate value as a screening tool for existing genetic material.  The team’s parallel assessment of two RL varieties, for instance, reveals significant differences between them in larval success (Figure 2). 

“With sufficient support we could screen all current and emerging varieties as well as breeder’s lines and hybrid parents for tolerance to both adult feeding and larval success,” says Prof Penfield. “This would give growers a valuable head-start as far as genetic solutions are concerned.

“As well as genetics, our work with many generations of the pest over the past five years has given us a much better understanding of what makes cabbage stem flea beetle tick,” adds Dr Wells.  “It wouldn’t take much additional funding for us to develop a good initial model of flea beetle population dynamics based on key environmental variables. Continually refined with field experience, this could form a crucial resource in both predicting levels of local risk and testing management strategies.”

 Figure 1

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Source: John Innes Centre

Figure 2:

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*A and B are two different varieties at both high and low egg pressures.

Source: John Innes Centre

How variety choice could help reduce damage from cabbage stem flea beetle

Varieties that develop more rapidly in the autumn and earlier in the spring seem able to substantially reduce damage from cabbage stem flea beetle larvae as well as adults, according to the latest variety trials Agrii.

“We have undertaken almost 40 specific flea beetle management trials since 2009,” points out seed technical manager, David Leaper.

“It’s crystal clear from the whole range of approaches we’ve explored that no single one offers a reliable solution.  It’s equally clear that anything that gets in the way of early crop growth can significantly increase flea beetle impact.

“We’ve long found the fastest developing varieties in the autumn are better able to grow away from adult flea beetle grazing as well as coping more effectively with later sowing and more challenging establishment conditions,” he reports. 

“Across more than 40 varieties on four sites significantly affected by flea beetle in 2018/19, we also saw a very good correlation between the level of larval damage and speed of autumn development (Figure 1).”

Interestingly, the Agrii trials further showed the earliest varieties to grow away in the spring suffered the least stunting and main stem loss from flea beetle larvae (Figure 2).  Like the advantage enjoyed by faster developing varieties in the autumn, Mr Leaper puts this down to their superior ability to compensate through earlier growth and development.

Fast-developing varieties, DK Exsteel and DK Expedient stood out in the trials in both these respects. Even faster-developing in the autumn and very early to resume growth in the spring, DK Extremus promises to add to their advantages in combatting the flea beetle threat.

At the same time, the fastest-developing Clearfield varieties like DK Impressario CL have been showing a clear establishment edge for their tolerance to ALS inhibitor residues when grown in reduced tillage systems.

Figure 1:

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Figure 2:

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How OSR drilling date will influence cabbage stem flea beetle attack

While much of the focus of CSFB management is on early crop survival, minimising the damage from larvae is at least as important an imperative – both to ensure a profitable crop and to reduce future pest problems.

“We have to get the crop established, but it also needs to be profitable,” insists ADAS crop physiologist, Dr Sarah Kendall. “So, we must avoid falling into the trap of being happy to get through the autumn storm and to harvest anything much at all.

“We can’t afford to throw key elements of best management practice out of the window in dealing with flea beetle either. Otherwise, we’ll end up with difficult-to-manage canopies and crops that will always struggle to deliver the yields that make them worth growing.


“Instead, we have to integrate the most useful CSFB cultural controls carefully into the most productive management regimes. If this means changing when or how we establish the crop or manage it we must adjust other elements of our agronomy to fit.”


Such an approach is especially crucial given the findings of the detailed analyses of 14 years of data from more than 1600 sites undertaken by ADAS with Bayer and other industry partners in a four-year AHDB-funded integrated pest management project concluded this spring.

This analysis shows sowing date as the only grower-controlled factor having a significant effect on the pest. Unfortunately, though, the relationship is nowhere near as simple as many have assumed.

“Our modelling confirms August drilling minimises adult damage,” explains ADAS entomologist, Dr Sacha White. “However, it also shows the earlier the sowing the greater the larval burden is likely to be; mainly because of the amount plant growth available to support adult feeding and egg-laying over an extended period (Figure 1).”

Dilemma

This presents a serious dilemma. Sow earlier and you are more likely to have a crop. But you are also more likely to have a crop full of larvae that yields poorly and may have to be abandoned later in the season.

Alternatively, sow later to minimise the larval challenge and risk not being able to establish a viable crop because it emerges into higher levels of flea beetle activity and is far more vulnerable to adult grazing.

“It’s not an easy decision,” Dr Kendall agrees. “On balance, I favour sowing later because, if I have to, I prefer replacing a crop before investing too much time, effort and money in it.

“We also know from experience that, even on heavy ground in East Yorkshire, it’s perfectly possible to bring in over 4.5t/ha from mid-September sowing at 26 seeds/m2 with the right combination of variety and early crop management.

So, what strategies does ADAS evidence and experience suggest might be valuable for earlier and later sowing – or indeed both?

Well, Dr White and Dr Kendall insist that drilling into moisture – rather than the hope of it – is fundamental. As are good seedbed conditions, a consistent sowing depth and effective rolling for maximum seed-to-soil contact.

More than anything else, perhaps, this means knowing when not to sow OSR and – again like black-grass management – having enough rotational flexibility to sow something else instead.

The ADAS analyses show no benefit from increasing seed rates. There is a tendency for higher seed rates to reduce percentage leaf loss, and they definitely result in higher plant populations. However, seed rates appear to have no discernible effect on larval numbers per plant. Higher sowing rates, therefore, simply mean more larvae per field.

“While higher seed rates with farm saved seed may help crop survival, we generally find little yield benefit from rates of more than 40 seeds/m2,” reports Dr White. “Add the extra risk of weaker plants, the danger of less productive canopies and the risk of higher pest populations for the future, and we really wouldn’t advise pushing-up rates.”

Interestingly, the analyses suggest a tendency for less beetle damage with declining intensities of cultivation; a finding supported by a recent BASIS project revealing markedly lower larval numbers in direct drilled crops, but one needing far more investigation before any firm conclusions can be drawn.

As yet, ADAS also has insufficient science to support companion cropping. However, their studies across several sites over two years are showing that delaying the control of volunteer OSR from the previous season can give significant reductions in adult numbers, feeding damage and larval populations in neighbouring crops (Figure 2).

“This technique has obvious promise because we know flea beetles use the breakdown products of glucosinolates produced by OSR to locate crops and can’t distinguish between planted crops and volunteers,” Dr White points out. “Once they’re feeding and mating their wing muscles weaken, making them much less mobile, so they’re trapped.

“To be effective in diverting flea beetles from planted crops, our trial work shows the volunteer trap crops need to be close by and left green until late September. This can take valuable pressure off OSR crops at their most vulnerable stage, and would fit particularly well where wheat crops are being drilled later in the battle against grassweeds.”

Winter defoliation

Another technique showing promise for larval control, in particular, in ADAS work is winter crop defoliation – either by cutting or with sheep grazing. Drastic though this may be, both plot trials and field-scale investigations have resulted in significant reductions in larvae.

“Providing the defoliation is ahead of stem extension and spring growing conditions are reasonable this can be done without significant yield loss,” says Dr White. “To be safe, I’d always defoliate before the end of January. I’d also only do it with a well-established crop, so it’s probably more suitable – as well as necessary – following earlier drilling. And I’d want a variety that was especially vigorous in its spring growth.”

Whatever approach is taken, Dr Kendall insists it’s essential to have a firm and well-integrated strategy that marries key elements of flea beetle management carefully with established best OSR growing practice.

“Earlier drilling, for instance, needs to be accompanied by much more focus on controlling larvae and spring canopy management,” she urges. “It’s also likely to require varieties with particular resistance to phoma and light leaf spot and first-class standing ability; plus a careful watch-out for early season pests like cabbage root fly.

“Equally, drilling later will put the onus on the most vigorous, fastest-developing varieties; particular attention to seedbed conditions and management; and, a spring programme involving earlier nitrogen, sulphur and low rate PGRs.

“In our experience healthy, well-structured soils with good levels of organic matter make all the difference in dealing with the extra risk that flea beetle brings,” concludes Dr Kendall. “They are as important as any other single element of an integrated pest management approach.”

 

Figure 1: Relationship between drill date and CSFB larval populations in the autumn.

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 Source: ADAS, 2020; AHDB-funded CSFB IPM project

 

Figure 2: Mean numbers of adult CSFB caught in yellow water traps in new OSR crops adjacent to a field in which vOSR had been controlled early or late

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Source:Non-chemical control options for cabbage stem flea beetle in oilseed rape.
            S White, S Ellis & S Kendall. Aspects of Applied Biology 141

How to assemble a plan to beat cabbage stem flea beetle in OSR

Extensive Agrii research across the country over the past 11 years shows that, like black-grass, a jigsaw of cultural controls can really help beat the beetle.

In the same way as black-grass, though, these need to be applied alongside one another with careful planning that is firmly based on the degree of field risk, starts with the rotation, and has sufficient flexibility to cater for different conditions – especially soil moisture.

“It’s vital to appreciate that insufficient moisture or excessive pressure from the pest at establishment means we are likely to be fighting a losing battle whatever we do,”

stresses trials manager, Steve Corbett.

“So, we need to have a wide enough rotation to restrict the build-up of local pressure and, dare I suggest it, avoid the sort of block cropping that really concentrates flea beetle populations. And, of course, we shouldn’t even consider sowing rape unless and until we have sufficient moisture in the ground.

“Just like black-grass with wheat, the rotational flexibility not to sow OSR when the risk is too high is fundamental. As is having the right crop ahead of it. Mainly because, time and again, all our work in high CSFB pressure areas of the country highlights the overwhelming importance of presenting a barrier to the beetle which minimises the ‘green on brown’ attractiveness of the young rape crop.”

Agrii’s field-scale trials at Chiseldon in Wiltshire last season, indeed, showed average shot-holing damage in a crop grown on bare ground was twice that on ground with a good covering of winter barley debris.

At Langley in Essex in 2018, there was a more than threefold difference in leaf damage between a young crop in bare soil and one with decent straw and chaff coverage. And, averaged across varieties and other treatments in 2019, the difference in damage between a crop sown into high (12”) and low (3”) stubbles was almost as substantial at the AgriiFocus technology centre (Figure 1).

“Across a 70 acre field at Eyeworth in Bedfordshire last season, we saw massive differences in damage where areas of the preceding wheat crop had been sprayed-off for blackgrass,” adds Agrii head of agronomy, Colin Lloyd. “In marked contrast to the evenly established crop with almost no shot-holing in the bulk of the field, the sprayed-off areas without any straw cover were devastated, with hardly any surviving plants.”

 

Companion cropping

Where a preceding fallow, spring barley or straw crop baled for sale means little, if any, decent cover, Mr Corbett suggests a nurse or companion crop could offer a valuable alternative CSFB barrier. However, his experience underlines the need to plan and manage these options very carefully as well as the extent to which the weather can defeat the best laid plans.

As nurse crops, buckwheat and, to a lesser extent, fenugreek sown in late July into reasonable moisture conditions last year noticeably reduced flea beetle damage in OSR sown three weeks later in his trials at Saxby Cliffe in Lincolnshire.

However, at Throws Farm buckwheat nurse crops sown in early July into much drier soils resulted in poor establishment and relatively high levels of damage to OSR sowings two weeks later – up to 37% on bare soils and 20% with decent stubbles.

As a companion crop, buckwheat drilled at the same rate with the OSR did a much better job, keeping average CSFB damage down to 3.5% against the 24%  average of the nurse crop plots.

“In other trials, we’ve seen a buckwheat companion crop do as well in reducing shot-holing as some promising new seed treatments we’ve been investigating,” points out Mr Corbett. “In this case, as a nurse crop lack of moisture meant it couldn’t get away and provided far too little cover. In contrast, the companion plots were sown into more moisture.

“Having said that, we’ve also found nurse crops can grow far too well, shielding the rape planted into them but, at the same time, compromising their establishment. And we’ve seen companion crops be a waste of time and effort when they haven’t had enough moisture.

“Like the crop itself, sufficient moisture is the critical factor. Equally important with companion cropping, in particular, our work has shown is using the right variety of buckwheat at the right rate and sowing it at the right depth.

“The two varieties we’ve been studying are like chalk and cheese. Common buckwheat is far thinner, more spindly and runs to flower too rapidly to give a decently sustained cover, while the alternative establishes a much better canopy and gives more extended protection to the young rape. At the same time, the size and shape of the common buckwheat seeds means they separate out more from the OSR in single hopper drills, leading to less even crop cover.

“It’s a jigsaw of agronomic support we have to put together here – including minimal soil disturbance at drilling, fast-developing varieties, good seedbed nutrition and timely early insecticide spraying as well as long stubbles, good soil cover and/or effective nurse or companion cropping,” he explains. “It’s a complicated business getting all the pieces in the right place.”

 

Variety

Agrii regional technical adviser, David Felce who farms at St Neots agrees that putting it all together is by no means easy. However, he has no doubt about the value it offers.

“A good seedbed with sufficient moisture is crucial,” he insists. “Otherwise it really isn’t worth bothering with OSR these days. Spreading slurry or digestate can really help get the crop away. But these need to be incorporated and we know it’s important to minimise soil disturbance for the least ‘green on brown’ flea beetle attractiveness. So, there’s a clear dilemma here.

“Whether it’s a hybrid or pure line, a fast-developing variety is important too. This is crystal clear in our trials and in the field.  However, we’ve found no value in increasing seed rates as a defence. This only leads to thinner-stemmed crops less able both to tolerate larvae and to branch away from them in the spring.

“Our work shows the value of protected phosphate together with a balance of nitrate and ammonia N and immediately available boron in the seedbed as a specialist starter fertiliser. It also underlines the contribution lambda-cyhalothrin can make when used at the best time – crop emergence.”

Putting these elements together, Colin points to results from the latest Throws Farm trials with one of the fastest developing OSR varieties available (DK Expedient) sown at two seed rates with 12 different establishment programmes and three sets of drilling conditions.

Averaged across the cultivation methods and seed rates, the recorded damage levels clearly demonstrate the value of stacking  the controls in exactly the same way as black-grass management.  

As the package is built from a relatively poor nurse treatment crop at one end of the scale to a decent companion crop plus specialist starter fertiliser and early pyrethroid spray programme at the other, so flea beetle damage declined from an average of almost 25% to virtually zero (Figure 2).

“This says it all,” he concludes. “Unless you are faced with too little moisture or your recent crop experience suggests the pest pressure is likely to be too high – in which case you shouldn’t be sowing OSR – you can beat the beetle. And you can do so very economically too.  But only if you are willing and able to give it enough care and attention with the right pieces of the cultural control jigsaw for your own conditions.”

 

Figure 1: Adult Flea Beetle Damaage in AgriiFocus Trials 2019

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 Source: Agrii 

 

Figure 2: Throws Farm CSFB Establishment Trial 2019
                Damage by Programme (Averaged across Cultivation Method and Seed Rate)

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Source: Agrii 

Why an integrated control approach is needed to beat CSFB

With many years of frustrating commercial and trials experience with flea beetle behind him, Hutchinson’s technical manager, Dick Neale believes a well-integrated approach to managing the pest is essential. More than this, though, he is convinced the whole industry needs to take a longer-term view of the problem if OSR is to continue to be viable.

“For just about every possible management technique, we have as many growers who find it doesn’t work as those who believe it helps,” he stresses.

“This season we put a wide combination of elements together in our trials – leaving a long stubble, choosing a high vigour variety, using a starter fertiliser and upping seed rates. We even managed to sow into some decent moisture. But we still lost the lot, regardless of when we sowed.

“Waves and waves of migrating beetles in dense swarms like aphids on an early summer day completely overwhelmed the crops. Under these conditions, it makes no difference how many we divert into trap crops, confuse with companions or manuring, or intercept in spider’s webs. These are just the tip of the iceberg.”


Frustrating to Mr Neale too is the lack of association between autumn pest pressure and the number of beetles seen at harvest, making it impossible to use this as any reliable predictor of problems.

Under these circumstances, he insists our whole approach to management has to be based on the biological fact that fields with high levels of flea beetle larvae will inevitably generate large adult populations going forward.

“The solution is simple,” he reasons. “Where we have big problems in an area in spring we have to sow less rape the following autumn. Growing beans or linseed as an alternative break will break the flea beetle cycle, allowing us to go back to OSR again.

“At the same time, of course, we must up our establishment game with well-researched variety-based management recipes for earlier and later drilling based on the best field-scale trial evidence.

“This has to include not having more OSR in our plans than we can reasonably sow in a
4-5 day window; only sowing when – and if – we have enough moisture in the ground; and reining back on pyrethroid spraying to give predators a chance.”

Once flea beetle pressures have declined, trap and companion crops could be useful additions to help keep them in check, Mr Neale believes. Winter defoliation could have a place too, although the consequences for crop recovery, pigeon and weed control need to be very carefully considered. And screening may allow varieties tolerant to adult feeding or larval development to be added to the mix.

“Overall, it’s probably only sustainable to grow OSR one year in five or six,” he suggests. “Which means a national crop of around 500,000 ha – not the 750,000ha it had reached,
or the 350,000ha it may have declined to by the coming harvest.

“Just like wheat-growing on bad black-grass ground, a combination of sound rotational and other cultural controls in a determined recovery plan offers the only solution to CSFB in my view. It’s a radical rethink we need. Tinkering at the edges won’t do any good.”

Companion cropping

Pioneering Agrovista trials in the early days of the neonicotinoid ban showed a reduction in flea beetle larval burdens from berseem clover as a companion plant. And more recently the company has seen good results from combining companion cropping with other elements of OSR agronomy.

Overall, technical manager, Mark Hemmant sees the primary benefit of companion cropping coming from the extra help it gives OSR to grow away from CFSB.

“Our original studies focussed on capturing nitrogen and improving soil condition,” he says. “These continue to be vital considerations today. But the real value we have found from companion crops is in improving rape establishment.

“While berseem clover’s top growth is relatively restricted – so it doesn’t compete with the crop – strong tap roots really open-up heavy soils, in particular, making them far more friable and much better drained – which OSR appreciates massively.

 “Using just 2.5-3 kg/ha of seed costing £10/ha or less, we’ve seen marked improvements in

rape root development, root diameter and establishment rates. As well as enabling the crop to survive reasonable levels of adult flea beetle pressure, this ensures it is big and strong enough to tolerate the larvae.

Mr Hemmant insists that companion cropping is only one weapon in the establishment improvement armoury, and urges growers to employ the most effective cultural controls for their particular circumstances.


Preserving moisture

To preserve moisture at drilling while achieving the best seed to soil contact, he prefers seeders that move trash out of the way, cultivate within the slot and disturb the least amount of soil on the surface to simple direct drills.

His trials with longer stubbles have shown useful reductions in flea beetle damage by producing a better micro-climate for the OSR, although their value has varied between seasons. The work has also pointed-up need for drills that can cope with such stubbles and still sow evenly and close the slot consistently.

“Having battled devastating cabbage root fly in crops near gardens growing brassicas, I wouldn’t sow rape before mid-August unless conditions are near perfect,” Mr Hemmant advises. “Especially not, as the earlier you sow the more flea beetle larvae you get.

 “I consider varieties that develop fast in the autumn and spring essential these days, regardless of drilling date. The imperative is to get the crop away, and most growers I know would be more than happy to have a crop needing positive growth regulation.

Clearfield varieties may have a useful edge for their ability to tolerate residues and the fact that they allow broad-leaved herbicides which can also hold the crop back to be delayed,” he adds.  “Because we can’t really control flea beetle, doing everything we can to help the crop tolerate both adults and larvae has to be our priority.”

Organic manuring

Organic manuring ahead of drilling can noticeably reduce damage from both cabbage stem flea beetle adults and larvae as well as improving crop establishment, according to the latest Royal Agricultural University study. But its value very much depends on the type of manure.

The current season study by undergraduate student, Ted Allen-Stevens with Dr Nicola Cannon shows well-rotted chicken manure delivering better results than either digestate or cattle muck across 1ha direct-drilled plots in an early September-sown Gloucestershire crop.

“The warm, dry weather in mid-September really impeded crop establishment and heightened flea beetle activity,” reports Mr Allen-Stevens. “Thankfully, a combination of two pyrethroid sprays and cooler, wetter conditions from the last week of the month turned the tables in the crop’s favour, allowing all but the control plot to establish satisfactorily.

“The extra pressure of the wet winter led the control plot to fail completely, while the manured plots came into the spring with average populations of between 24 and 48 plants/m2.

“Cattle muck was the least successful of our treatments,” he explains. “Even so, the 20t/ha we surface applied the day before drilling – supplying 8.5kg N/ha – led to higher average October and February plant counts than the control.  Similar levels of shot-holing/plant in the autumn and larvae/plant in the late-spring suggests its value here was entirely nutritive.”

Unsurprisingly, given the higher levels of N supplied, 20m3/ha of digestate and 9t/ha of chicken manure both markedly improved autumn and spring plant populations. They also resulted in less shot-holing and fewer larvae/plant.

Very surprising, though, were the noticeably higher autumn and spring plant populations and lower levels of adult and larval damage with the chicken manure which supplied just
13.1 kg N/ha compared to the digestate supplying 62.2kg N/ha.

“Despite containing only around a fifth of the nitrogen and in a less readily available form than the digestate, the chicken manure came out on top  in every respect, with the possible exception of very early plant counts,” Mr Allen-Stevens points out.

“Both these treatments appear to have had a deterrent effect on adult beetle feeding –  masking the isothiocyanate exudates from the crop known to attract them, perhaps; an effect that would naturally feed through to lower larval burdens.

“Chicken manure was the stand-out here.  Like the digestate, it gave more even ground cover than the cattle muck. It also had a much stronger effluent effect (odour) on application.”

 

Figure 1: Fairford Organic Manuring Trial Findings 2019/20

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Source: Ted Allen-Stevens; Royal Agricultural University 2020

Further reading