Last autumn’s difficult establishment and high cabbage stem flea beetle pressure saw significant crop failure for most of the iOSR grower group. While remaining crops look healthy, what will be the impact of the losses?
The key question for iOSR growers is just what impact the high levels of cabbage stem flea beetle (CSFB) larvae are going to have on yield?
The threshold for yield effect has been set as low as just five larvae per plant, yet most crops are reported with infestations well in excess of this number, with iOSR growers across the country seeing populations of 20-40 or more larvae per plant.
iOSR meeting host Ian Lutey, manager for R.H. Topham, St Ives, hoped keeping crops as healthy and green for as long as possible could help mitigate against the effects of CSFB larvae.
He applied Amistar and trace element manganese at mid-flowering, as much for the physiological stress relief and greening as the sclerotinia protection.
“The effect of larvae damage is evident in almost every plant,” he said. “In some it is restricted to the side branches, so we may lose some of those but retain the rest of the plant. In others the main stem is damaged.
“We do not know what impact it is likely to have on final yield, but everything we can do to keep the plants healthy to the end has got to help.”
Northamptonshire grower Jeff Bradshaw had also used Amistar to extend the green leaf retention of his remaining crops which were looking healthy, but also showing extensive sign of CSFB.
This year he also planned a late N application at the end of flowering to push yields.
Norfolk grower Chris Eglington aims to establish big, strongly branched plants at populations of 15-20 plants per sq.m by using precision drilling at low seed rates.
With his multi-branched plants, Chris believes there is still potential to achieve good yields, even with some losses, but he acknowledges this season the CSFB larvae pressure is unprecedented.
FOR Cambridgeshire grower, Ian Lutey the demand for stronger growing plants has seen a switch to growing all hybrid varieties.
“We used to grow a mix of conventionals and hybrids, with the latter on more difficult or later sites,” he said.
“Now we look for hybrid vigour initially for establishment, but more importantly in spring to get crops away and build a good structure canopy, in part to outgrow CSFB effects.”
When selecting varieties, he now puts as much emphasis on the growth habit and health of the variety, including rooting vigour, as he does the yield figures from the Recommended List.
SYNGENTA technical manager Georgina Wood explained an ingenious and simple technique to assess CSFB larvae numbers, which would help growers calculate the potential impact on yield from different levels of infestation.
“Lay a sample of plants on chicken wire suspended above a plastic box with 50mm of water in the bottom, ideally in a greenhouse or somewhere light and dry,” she suggested.
“The larvae think the plant is going into natural senescence and drop out, as if falling to the ground to pupate, only they fall into the water and drown.”
The water can be drained through a sieve and the larvae numbers easily counted.
“It has also been evident from the significant variation in larvae sizes collected, just how prolonged the infestation pressure went on for this season,” she said.
MARGINAL gains from small tweaks at every stage of the OSR management could see a step change in yields and profitability, if growers can move closer to the crops’ yield potential, according to Sarah Kendall of ADAS.
It has been calculated that OSR has the capability to intercept 70% of available sunlight, which could generate the yield potential of 12 tonnes per hectare.
“Agronomic techniques, such as reduced reflectance of light by flowers and prolonging the green canopy for longer can all move the plant towards maximum performance,” she advised.
“But we also need to look at all the other factors to understand what is limiting a crop’s potential in any situation, such as root development, fertility or moisture availability.”
DIRECT drilling and higher seed rates have been two key learns from trials on the iOSR Focus Site this season, reported Georgina Wood.
“We also demonstrated the huge impact of barley volunteers due to moisture competition in such a dry season,” she said.
“Growers who have moved to more OSR establishment after hybrid barley should target vigorous volunteers early to prevent any check in OSR establishment.”
Jeff Bradshaw agreed that, in his experience, direct drilling OSR, along with diammonium phosphate down the spout, had been highly beneficial last autumn in the dry soil conditions, with fewer problems with slugs and less issue with CSFB.
However, he remained aware that, in a wet winter, the need to get water away from OSR roots was essential – so the technique was only suitable for where soil conditions and structure allows.
Georgina added companion crop trials had been successful, with planting in conjunction with mustard showing up to 58% reduction in CSFB larvae in the OSR, although the pressure was such that it still left significant numbers in each plant.
THE iOSR group is looking to work with the Yield Enhancement Network to initiate new ideas and further develop work from the iOSR Focus Site on a grower’s farm scale for the coming season.
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