Arable News

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Agronomy Update – November 2014

Oilseed rape diseases, aphids in cereals and spring cropping plans will be occupying Craig Green’s thoughts

Oilseed rape diseases, aphids in cereals and spring cropping plans will be occupying Agrovista agronomist Craig Green’s thoughts over the next few weeks.Oilseed rape will need watching closely for disease, due to August rains and the more recent unsettled spell. These bouts of wet weather will have encouraged phoma spore production and release, says Norfolk-based Agrovista agronomist Craig Green (pictured above).”The usual threshold is 10-20 per cent of plants infected with at least one lesion. However, backward crops are more at risk from phoma as small leaves and short petioles allows the disease to reach stems quickly.”I’d advise applying 0.25-litres/ha of difenoconazole as a low-cost holding spray at the first sign of disease, plus foliar phosphite to encourage growth.” The fungicide should keep crops clean through to four leaves, when he’ll reassess tactics.More forward crops will be treated as soon as they reach threshold, says Craig. With flusilazole now revoked – stocks had to be used by 12th October – he’ll recommend Frelizon (also sold as Refinzar), a combination of penthiopyrad, an SDHI, and picoxystrobin.This new product controls phoma and light leaf spot and is more persistent than flusilazole. “Frelizon has also been shown to have rooting and greening benefits which helps set the crop up well for winter.” Plans for late-autumn grass weed control in oilseed rape should be taking place, he advises. “Propyzamide (eg Kerb) is best applied in November when conditions turn damper and colder. It’s a good opportunity to control black-grass and other weeds with different chemistry and it can be tank-mixed with Frelizon which can save a pass if disease does not come in too early.” Slugs pose a threat to cereals after recent rain, says Craig. “Most cereals went into good seedbeds and we have not seen many slugs so far. But a fresh egg hatch is imminent following the break in the weather at the start of the month.”Growers must stick to metaldehyde stewardship guidelines and should consider a ferric phosphate pellet such as Derrex if they are near the 210g/ha August-December limit or if the weather turns really wet, he notes. “Derrex is also the preferred choice for control of juveniles or in colder weather.”Aphids need monitoring, especially on early-drilled cereals where Redigo Deter (clothianidin + prothioconazole) seed dressing will soon run out of steam. “It lasts a maximum of six weeks and we have seen very high aphid numbers, so BYDV pressure is likely to remain high. Single-purpose-dressed late-drilled crops will also be at risk.”Apply a pyrethroid where aphids are present and re-assess regularly.” With pyrethroid resistance confirmed in grain aphid it will be important to monitor the success and treat with an alternative product if necessary, he adds.Grass weed control in cereals has got off to a good start in many fields, where pre-emergence graminicides were applied soon after drilling and rolling onto good seedbeds.Most fields had enough soil moisture to activate the pre-ems. If a follow-up spray is needed to control black-grass he’ll recommend Unite (pyroxsulam + flupyrsulfuron) or Atlantis (iodosulfuron + mesosulfuron) – both plus Auxiliary (clodinafop-propargyl + prosulfocarb).Unite also provides useful control of volunteer beans in cereals, ideally tackled at the 4-leaf stage, as can Spitfire (florasulam + fluroxypyr) if grass weed control is not required.More growers are cropping winter beans to help meet the CAP greening measures, says Craig. “There is a new EAMU for pendimethalin products allowing up to 1,320g/ha to be applied, which could prove very useful.”Nirvana (imazamox + pendimethalin) is scarce, so he’s planning weed control around Kerb + pendimethalin, or Linzone (clomazone + linuron) + pendimethalin where black-grass is absent.Craig reports a surge in interest in maize as growers, disappointed by 2015 prices, take a sugar beet holiday next spring. “Forward contracts show maize area already up a third for next year, but the AD plants can take a lot more,” says Craig.”We’ve had a bumper crop this year – the only limiting factor has been poor soil conditions, which have been evident after late-lifted roots or strawed crops.”Maize can be a less challenging crop to grow, but where it fits in needs some thought. I’d suggest slotting it in after a winter cereal to give it the best chance of performing.”* Craig Green is an agronomist with Agrovista, based at Great Ellingham, Norfolk ([email protected])


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