Arable News

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Agronomy Update

Early drilled oilseed rape is powering ahead but later-sown crops are lagging

Early drilled oilseed rape is powering ahead but later-sown crops are lagging. Both will require careful but very different management, says our Norfolk-based agronomist.
Agrovista agronomist, Craig Green.
The wet end to the summer means many oilseed rape-growing areas will be at higher risk of phoma attack this season.
The threshold for airborne spore production is at least 20 rainy days after 1st August, so growers will need to be on their guard for early infection, warns Norfolk-based Agrovista agronomist Craig Green.
“On more forward crops I’ll recommend Caryx (mepiquat chloride + metconazole), which has a new autumn recommendation, at the 4-leaf stage.
“It is also an excellent growth regulator – some of these forward crops were drilled in mid August to beat flea beetle and had four true leaves by the end of the first week of September. We have seen some excellent results in trials.”
Mr Green will follow with an application of Frelizon (penthiopyrad + picoxystrobin) at 0.5-litres/ha (+ boron) later in the year, targeting light leaf spot, which is increasing in prevalence across all rape-growing areas. The application will also provide further protection against phoma.
Frelizon will also boost growth of roots, enabling them to scavenge nutrients more effectively and optimise crop growth in early spring, he adds.
“In Agrovista trials we obtained 0.16t/ha extra yield using Frelizon at 0.5 litres/ha compared with straight prothioconazole at 0.35 litres/ha,” says Mr Green.
Backward crops will receive more fungicide and less growth promoter. Growers should not be tempted to stint, he adds. “We want as big a crop as possible going into the winter as they will have lot of pest and disease pressure to face on the way, so it is worth spending money early on.
“Small plants are more at risk from phoma so we need to be extra vigilant. A low dose of Difcor (difenoconazole) in October/November when disease is first seen will keep the crop clean, then I’ll follow up with Frelizon.
“Plants will also need feeding well, and I’ll use Terrasorb, an amino acid based product to boost vigour and plant development, at 2-litres/ha, as well as boron.”
AHDB guidelines are to spray aphids to protect against turnip yellows virus as soon as the first wingless aphid is seen. “Keep a close eye on winged aphids entering the crop and be ready to go,” Mr Green advises.
Biscaya (thiacloprid) at 0.3-litres/ha is the product of choice, as many aphids now carry knockdown resistance (KDR), which renders pyrethroids ineffective. The product can also be mixed with Caryx or Frelizon.
“This application will provide about two weeks’ protection, depending on weather and speed of plant growth – it is not translocated up the plant into new growth,” says Mr Green.
One point growers need to note is that where Centurion Max (clethodim) is used to control volunteers and start black-grass control, no sprays can be applied for 14 days before it is due to be applied or after application. “This requires some planning, as neither insects or disease can be controlled during that time.”
This season has seen a big uptake in companion planting, where berseem clover, +/- vetches, is sown alongside oilseed rape to improve crop rooting, scavenge nutrients and dilute pest pressure, particularly slugs. The companion crop then dies off or is sprayed after the winter to release nutrient back to the crop, while increasing soil organic matter.
“A lot of growers are trying this for the first time,” says Mr Green. “The clover roots were already a foot down in many cases by mid September, paving the way for oilseed rape, a lazy rooter, to get its own roots in deeper.”
*Craig Green is an agronomist with Agrovista, based at Great Ellingham, Norfolk ([email protected]).

  • Written by: Farmers Guide
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