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LAMMA 2021

LAMMA 2021

OSR varieties and establishment: Looking beyond neonicotinoids

The loss of neonicotinoid seed dressings should be nowhere near the issue for most British oilseed rape growers that many may have feared, according to some experts.


While it will make well informed variety choice and early agronomy more important than ever, it does not need to have a negative impact on yields or growing costs - unless, that is, it leads to knee-jerk reactions such as increased seed rates, which could do more harm than good.


This was the conclusion of an early summer growers’ round table discussion hosted by breeding and crop protection specialists Dekalb and BASF to explore the reality of an immediate future without neonicotinoid seed treatments on oilseed rape.

OSR Performance

Dekalb seeds and traits manager Deryn Gilbey said: “The loss of neonicotinoids is understandably concerning for growers, but we have to keep things in perspective.


“It is important to remember, for instance, we were successfully producing oilseed rape for more than 30 years before we had access to this chemistry.


“And this was with far less vigorous varieties and effective establishment systems than we have today. Also, a six to eight week period of activity meant they never entirely eliminated the need for autumn insecticide spraying.


“About two-thirds of the annual OSR crop is typically affected by the cabbage stem flea beetle and flea beetle pests the seed treatment is primarily targeted at.


“We know levels of infestation and crop damage vary widely from season to season, farm to farm and field to field. 


“Equally, regardless of the theoretical losses from turnip yellows virus (TuYV), the level of yield benefit from neonicotinoids in controlling its aphid vectors is highly questionable.


“Perhaps this is why there is no sign of any dramatic UK performance increase which could be linked to the introduction of neonicotinoids in the recent official yield record (see graph). 


“Indeed, the latest pesticides usage survey figures show about 30 per cent of the oilseed rape crop did not receive a neonicotinoid in 2010.”


Dekalb oilseed rape breeder Matthew Clarke has never used a neonicotinoid - or any seed treatment - when growing oilseed rape. He did not feel this has been any barrier to performance development. 


In fact, he saw selection in completely untreated situations as the best way of building the robustness he has always sought in hybrids.


He said: “By developing our varieties in the absence of neonicotinoids, we have been selecting for a high degree of tolerance to the pests and diseases they provide protection against.


“In particular, I am certain the vigorous fast-developing hybrids we have concentrated on breeding are far better able to tolerate both flea beetles and TuYV than varieties of the past.


“We have lost trial sites to flea beetle infestations on occasion, but this has been far from common, despite the fact that we grow more than 8,000 variety plots across the UK each year. We can tolerate far less variation in our trials than commercial growers can in their crops.


“Treated small plot trials seldom show them in their true commercial light, but vigorously establishing hybrids with the ability to grow away from infestations far more effectively than varieties which take much longer to get going in autumn will be essential for commercial crops grown without neonicotinoids,” said Mr Clarke. 


“Revealing in our work too is the fact plant populations make no difference whatsoever to the rate of trial or plot losses.


“If flea beetle infestations are sufficient to compromise a crop, they do so regardless of the number of plants.


“Increasing the seed rate to counter a possible threat is pointless. It will merely add to the expense if crops are lost, while compromising subsequent canopy management wherever autumn establishment is relatively trouble free.”


BASF agronomy manager Clare Tucker was equally adamant growers should avoid the temptation to increase seed rates in response to the loss of neonicotinoids, pointing out thin-stemmed plants were more vulnerable to damage from flea beetle larvae within their stems than thicker, more robust ones.


With risks both from pyrethroid resistance and to farming’s environmental image, she was also concerned to avoid an upsurge in blanket autumn insecticide spraying, wherever possible, especially given the great variability of flea beetle and aphid populations.


“More attention to early agronomy must be the main management priority,” she said. “If we can get crops away well, they are far better placed to withstand flea beetle damage.


“At the same time, they will cope with slug and pigeon problems better too. And they will be better able to tolerate early phoma infections, compete with late weed germination and survive challenging winter conditions.


“Anything we can do to respond to the neonicotinoid ban through improved early agronomy will deliver a whole host of additional benefits.”


Ms Tucker saw two clear elements of agronomic attention as important in this respect - ensuring the right establishment conditions, and early removal of the weeds which can interfere with crop development and subsequent performance.


Stressing soil conditions were always more important than calendar date in drilling timing, she identified good straw management, small soil crumb size and effective consolidation as the three key essentials to ensure the good seed to soil contact and adequate moisture supply throughout the germination period that oilseed rape needs.


”The sort of seedbed conditions which do OSR most good also promote the best possible efficacy of the co-formulated pre- or early post-emergence herbicides you really need to tackle problem grass and broadleaved weeds,” she said.


“Removing weeds or reducing their vigour early on allows crops to become more competitive for the most sustained weed control, as well as the greatest establishment effectiveness.


“Growing more vigorous, faster-developing hybrids and paying more attention to establishment agronomy will mean more forward crops wherever conditions are favourable.


“It is always easier to manage a larger crop than coax a backward one through an uncertain winter.  This can be done with metconazole to check top growth and encourage rooting and by adjusting spring nitrogen applications.


“On the spray front, it may well be necessary to integrate extra pyrethroids into the programme to keep on top of any early insect threats,” said Ms Tucker. 


“This will not be difficult or expensive to include with the early post-em herbicide or later with the graminicide or fungicide. It should, however, be done with care.


“We have yet to see pyrethroid-resistant flea beetles in the UK, but we know the peach potato aphid which carries TuYV shows

considerable resistance.


“We need to guard against further resistance development, as well as safeguarding our environmental image by avoiding blanket spraying.


“Under these circumstances, I see particular value in using simple insect water traps to monitor pest pressures and better inform and manage pyrethroid spraying.”


Roundtable conclusions

  • No point in increasing seed rates to counter plant losses to flea beetle
  • More attention to early agronomy a key priority
  • Getting establishment conditions right and early weed control will be key
  • Soil conditions more important than calendar date for drilling
  • Easier to manage a large crop than coax a backward crop through winter
  • May be necessary to use extra pyrethroids to keep on top of early pest threats
  • Use water traps to monitor pest pressure and inform pyrethroid spray decisions
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