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Measures for curbing club root At Lower End Farm, Brafield-on-theGreen near Northampton, Tim Care is battling a club root problem that came out of nowhere three years ago and now affects 17 per cent of his 400ha (988 acre) arable business. A single isolated patch of infection was identified in one field in the spring of 2014; a patch that was noticeable for its poor wheat performance the season before and initially put down to a previous soil levelling exercise. Club root was obvious when plants were dugup, however, and soil testing then showed the immediate area to be very acidic despite the field having no history of pH problems. By the following season, infections were apparent in patches across five fields, with the worst field yielding just 2.9t/ha compared with averages of up to 4.5t/ha in nearby unaffected ground. “What made matters worse, the previous crop of rape in the same field two years before gave us our best-ever spot yields at well over 5t/ ha,” said Tim. “The soil is a nice deep loam with no drainage problems.

Nothing – not even contractor’s machinery – had been brought into it and other affected fields in living memory either. They really are the last sort of places we’d ever have expected to see club root. So the problem would have been easy to miss if we hadn’t been on the lookout for it. “As one of the first in our area to grow rape and having been alternating wheat and rape in our rotation for over 20 years, I suppose it was inevitable we’d hit the buffers at some stage. Especially so as, if I’m honest, my brother and I hadn’t been as diligent with the liming as we should have been, relying instead on five-yearly testing and variable application as part of a precision service built around grid-based soil mapping. “Our move from ploughing to minimum tillage may not have helped either, concentrating any build-up of club root inoculum in the upper, warmer soil layers,” he reflected. “Nor would sowing in early to mid-August through the autocasting that has always worked

20% increase in net margin over Oilseed Rape

Tim Care (right) and Chris Letts examine clubroot infected OSR.

well for us here – not least in keeping black-grass seed near the surface and highly vulnerable to propyzamide.” Although he’d never previously encountered it, club root had always been in the back of Tim Care’s mind. But now, like black-grass, it’s very much centre stage in his management.

Addressing the issue To address it, OSR growing at Lower End Farm has been reined back to one in every three or four years, depending on field risk. At the same time, soil testing and liming have been stepped-up, drainage efforts redoubled and varieties with club root resistance grown in areas with known problems. In these areas the Cares are delaying their sowing until later on in August after later maturing wheat crops, although this is the peak season for flea beetle. They’re also prioritising vigorous fast developing rape varieties across the farm to counter any problem areas yet to become apparent. “Like black-grass here, I think Tim has been able to nip club root problems firmly in the bud by spotting them early and taking concerted action to address them,” reported Agrii agronomist, Chris Letts. “Driven by the black-grass imperative, a good measure of rotational ploughing and spring cropping should definitely be helping on the club root front too. “Winter OSR remains the most profitable crop after first wheat for most of my growers. So just 120ha

(300 acres) of winter rape a year here rather than the 200ha (500 acres) of the recent past will have an obvious impact on margins. Having said that, just like black-grass, it’s a matter of making short-term compromises for long-term sustainability – a delicate balancing act,” said Chris. “Club root is a growing challenge for many who may seldom, if ever, have experienced the problem before. As a soil-borne disease it’s almost certainly a threat we can never completely eliminate. So it’s important we take time to understand it, keep a close eye open for it and use all the cultural weapons at our disposal to keep firmly on top of it,” Chris stressed. “In particular, I believe there’s no substitute for getting out into the field and testing widely for any areas of acidity; especially areas where crop performance has been obviously falling below the field average. And everyone should be digging-up OSR plants that look to be suffering to check for clubroot as well as other tell-tale signs of soil problems. “I’m happy to say that an extra year or two between rapes in the Lower End Farm rotation is already paying dividends in yields,” observed Chris. “So this may go some way to making-up for the spanner clubroot has so clearly thrown in Tim’s longstanding rape-growing works.” ■


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12 May 2017

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