Oilseed rape abandoned in cabbage flea beetle ‘hotspots’
Monday 22 February 2016 11:27
This move to the riskiest crop in the rotation looks set to prompt many in cabbage stem flea beetle hotspots to abandon it altogether next season.
Between 1984 and 2013, the rapeseed area has increased from 300,000ha to 750,000ha, and provides an ideal break for the number-one cash crop, winter wheat.
A mix of tight rotations and rising insecticide resistance has allowed cabbage stem flea beetle pressure to build to unprecedented levels, particularly in Suffolk, Cambridgeshire, Bedfordshire and Hertfordshire.
However, this pressure was largely masked by neonicotinoid seed treatments, which help the crop establish under adult beetle attack in the autumn, from the early 1990s until they were banned in December 2013.
Warning signsFor Prime Agriculture agronomist Andrew Blazey – covering Suffolk, Cambridgeshire and Essex – warning signs of a major problem appeared in spring 2014 when significant damage from flea beetle larvae was evident.
“You could see small, stunted plants in backward areas, caused by larvae moving into the stems and damaging secondary racemes,” he explains.
This betrayed the presence of an already high background pressure before the insecticide seed treatments were even banned and, in autumn 2014, the “perfect storm” rolled in.
A neonics ban, combined with a warm and dry September, meant crops were hit hard by adult grazing and plants struggled to grow away from the attack.
Mr Blazey says this caused about 10% crop loss locally, with some growers losing up to 100% of their area. However, the real nightmare came in spring 2015.
Spring damageWith 50% or more of the variable costs already invested in crops, including £62/ha in extra insecticide applications to control flea beetle and peach potato aphid, the stakes were already high as plants began to go backwards.
“Spring flea beetle damage is much worse than autumn damage in my opinion – at least with autumn damage you can see when you should bail out.
“But if you have crops starting to die back in the spring, despite insecticide treatments in the autumn, it’s a real kick in the teeth,” he says.
As a consequence yields suffered, patchy and open crops allowed blackgrass to thrive and caused uneven ripening, but the propagation of flea beetle is something Mr Blazey describes even more “frightening” going forward.
DerogationWith ideal growing conditions and armed with derogation for neonics use, growers in his area lost just 2% of the oilseed rape drilled last autumn.
But despite the seed treatment and three pyrethroid sprays, the frightening propagation of flea beetle has continued this spring; as huge larvae numbers are again decimating crops in hotspot areas.
Mr Blazey says oilseed rape is now causing serious agronomic challenges and hindering the aim of achieving a sustainable farming system across his clients’ acreage.
“The patchy crops are letting us down in terms of blackgrass and broadleaved weed control, and even with seed treatments, the problem is now too far gone.
“If we don’t get the yields this year, I think many of my growers will call it a day [with oilseed rape] for the time being,” he adds.
Crop lossesOne grower that has already made the decision to move away from oilseed rape is Cambridgeshire-based James Peck.
The 2,225ha of land PX Farms manages is split between fenland around Wisbech and Emneth, and heavier land further south near Cambridge.
While oilseed rape is not grown on its black soils, it has been an important part of the rotation on its heavy land since the early 1980s.
So far, there had been no historical oilseed rape losses for the business, despite using conventional, home-saved and non-neonicotinoid-treated seed.
However, that soon changed when Mr Peck took on a 173ha farm near Bourn, west of Cambridge, in 2012, which had been in continuous wheat for 27 years.
In autumn 2014, he introduced oilseed rape as a break, coinciding with the first season neonic seed treatments were unavailable.
“After four insecticide sprays [to control flea beetle] and before going for the fifth, something just didn’t sit right with me, so I put some Roundup in the tank and sprayed it off,” explains Mr Peck.
Counting costThe whole block was replaced with conventional winter barley, which did not perform well enough to cover losses from establishing the failed rape crop, which totalled £301.45/ha.
Mr Peck decided to plant oilseed rape on the block again in 2015, but this time with neonic-treated seed obtained under the derogation.
While some of the crop survived the adult flea beetle onslaught, a further 73ha was lost. Mr Peck estimates the total cost to the business over the two seasons was in excess of £87,000.
“As our business is based on a model of contract farming for other people, so we need to ensure we do a good job and make a profit. We just can’t afford these crop and financial losses,” he explains.
As a consequence, the farm’s winter wheat and oilseed rape rotation on its heavy land will now be replaced by a more diverse sequence of crops that includes white mustard, peas and sugar beet.
“The plus side means there is more diversity in the rotation, but the negative is that we are doing less for the bees, as a major food source is taken away,” explains Mr Peck.
Big decisionsAcross the county border at Eyeworth, Bedfordshire, grower and AHDB chairman Peter Kendall says the fall-out from the flea beetle epidemic will mean some big cropping decisions for those in hotspots this autumn.
He has already cut back his oilseed rape area since the neonicotinoid ban following crop losses of his own and says the industry has a “massive problem”.
“Growers may take the view that there is no competition when choosing a break crop, but we need to be clear on the severity of the situation.
“Some may need a number of years away from oilseed rape to get flea beetle numbers down,” says Mr Kendall
Is oilseed rape worth the risk?With depressed prices, now might a good time to “leave oilseed rape behind for a period” according to AHDB Cereals and Oilseeds lead analyst, Jack Watts.
Between 2011 and 2013, the rapeseed price at the Erith-based ADM crush hovered at £350-£400/t and provided good financial returns, but it has since plummeted to about £250/t.
Mr Watts has used typical yields and costs to calculate the effect of current low prices and potential crop losses on net margin and it clearly illustrates current financial risks for growers.
While many areas unaffected by flea beetle will not be exposed to as much risk, those in the hotspots will look at the figures with fear, with net margin squeezed as losses increase.
“As a starting point, you are losing £200/ha before you have even started to integrate any lost area or yield. Where is the incentive to take that risk?”
Mr Watts says taking an “agronomic break” from oilseed rape could be worthwhile to reduce pest pressure and placing growers in a better position to take advantage of better prices in the future.
However, Mr Watts acknowledges the difficulty of finding a viable alternative, with the danger that minor break crop markets could be overwhelmed.
For example, just a small proportion of the large oilseed rape area shifting into bean markets would be proportionally significant and supply is already a problem for beans as a result of the three-crop rule and greening.
Mr Watts says that if growers cannot find viable break crops, they will have to turn to spring cereals to do the job economically.
“They are interesting as a break from oilseed rape and also a blackgrass control perspective, too.
“Many are turning to double spring cropping of spring wheat, followed by spring barley for that purpose. It is certainly something to consider if you aren’t willing to take the risk [on oilseed rape],” he says.
All contributors were speaking at the recent British Crop Production Council (BCPC) Pests and Beneficials Review 2016 in Cambridge, titled “Can we continue to grow oilseed rape in the UK?”