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Weed control, both short and long term, has come to the fore this month for Norfolk-based Agrovista agronomist Craig Green.

Craig Green has recently discovered that flying a drone across maize fields is picking up eyespot before he can usually see it.

Variable oilseed rape emergence is evident in my area of Norfolk, directly related to seedbed moisture and subsequent rainfall. Less pre-emergence spraying has been carried out as a result, either due to the weather or because growers have waited to see how crops establish. Although metazachlor is an option, and propyzamide is an obvious choice later in the autumn, both are relatively

expensive for growers that are not troubled by black-grass, which remains the case for most of my clients. This season I’ll be using Parish, which contains 320g/litre of phenmedipham, to control a similar range of broad-leaved weeds to metazachlor, as well as cranesbill. At under £20/ha it’s good value for money and brings more flexibility. Applied between cotyledon and two true leaves of the weed and before nine leaves of the crop, it will be a very useful addition to this season’s armoury. Although black-grass remains a relatively minor problem in my area, it and ryegrass are increasing, especially on the heavier land along the A47 corridor. This is the first year I have seen poor levels of control from a decent residual stack based on flufenacet, and a follow-up Atlantis. Where that’s the case, I’m advising growers not to rely on chemical control alone, but to delay drilling wherever possible to allow more time for weed seeds to germinate and to maximise pre-drilling control with glyphosate.

Anything we can do to reduce early pressure is vital. Sowing a wheat variety with a ground-hugging, spreading growth habit will help it outcompete black-grass plants which are trying to establish at the same time.

Prolific tillering Belepi is ºprolific at tillering – so much so that we need to reduce seed rates even when it is sown towards the end of the year. It might be slightly off the yield pace being set by Recommended List heavyweights, but it is known to be highly competitive, which helps offset that yield gap where grass weed pressure is building. A lot of customers are giving the new liquid Avadex (tri-allate) formulation a go this season. Although it only delivers 75 per cent of a granular application, people have until now not used the chemical at all, as the solid form required a specialist applicator. Applied as soon as possible after drilling, Avadex should really give black-grass a headache, and it will be a valuable addition, especially where weed numbers are relatively low. At under £40/ha it should be costeffective, and will take the pressure off

other chemistry in the stack. To help tackle the growing blackgrass pressure in the county, I’m setting up four large-scale trials on four fields on four different farms, all within a three-mile radius. The idea is to look at what difference different drilling techniques, cover crops and chemistry can make. Each farmer will be trialling their own methods against ours. We hope to run these over several seasons and open up the trials to local growers so they can see the results for themselves. Maize harvest has just started. Although about two weeks early, indications are that yields will be good, despite the dry, cold start. The benefits of good weed control are clear to see – delays or bad scorching early on have reduced yield by several percentage points. I’ve recently discovered that flying a drone across maize fields is picking up eyespot before we can see it. This will help growers prioritise these areas for harvest, helping to minimise leaf loss and maintain yield and quality. Craig Green is an agronomist with Agrovista, based at Great Ellingham, Norfolk ( ■

AGRONOMY UPDATE – WEST Growers affected by black-grass will need to keep a close eye on oilseed rape crops this season to maximise control opportunities, writes Wiltshirebased Agrovista agronomist Esme Shephard. Oilseed rape growers have traditionally based their initial grass weed control on a pre-em spray followed by a contact such as Falcon (propaquizafop) or Fusilade (fluazifopP-butyl) to clear up volunteers. It looks as though this will be a good strategy this season, with many crops in my area of Wiltshire going into good, moist seedbeds that should help optimise pre-em activity. However, some growers are now omitting the pre-em spray, preferring to ensure they have a viable crop that has outgrown the attention of flea beetle and slugs before committing money to chemistry. In these cases, black-grass will be more difficult to control. Some plants will be too big for propyzamide to control adequately – that chemical needs to be applied when it is cold, so won’t go on until mid November onwards. We will therefore need to apply something beforehand to keep black-grass in check.

I’ll be recommending Centurion Max, which contains 120g/litre of clethodim. Applied at the recommended 1-litre/ha rate, this is active on black-grass that is resistant to other ACC-ase-containing products and it will take out volunteer cereals as well. Centurion Max might not always result in a complete kill, but it will stunt the black-grass plants and slow subsequent growth, making them much more susceptible to the late autumn/early winter application of propyzamide. However, there are several caveats to observe to ensure crop safety and to optimise performance. Crops should be robust, so need to be adequately waxed. A 10-day no-spray period should be observed before application. Crops should also be growing well, so adequate nutrition is necessary. Centurion Max should be applied when the temperature is 8ºC or more. Cold weather,

particularly frosts, must be avoided. The chemical should be applied in 200-litres/ha of water as a medium spray to optimise coverage. In hard water areas, be sure to add a water conditioner, such as Stingray at 200ml/ha, to improve efficacy. A non-EC pyrethroid insecticide to control cabbage stem flea beetle can be tank-mixed if required. No other tank-mix partners are permitted. No herbicides or fungicides should be applied to treated fields for 14 days after application, while a 7-day period should be observed for nutrients and insecticides. Timing is important. Centurion Max should only be applied once the crop has two true leaves. The cut-off date is the end of October, although crops drilled on or before 25 August and early flowering varieties (6 or above) should not be sprayed after the middle of that month.

Winter wheat Winter wheat growers who struggle to control black-grass with their preem stack might want to consider an early post-em treatment. It won’t be cheap, but it is likely to be more costeffective than allowing the infestation to flourish or writing the crop off.

Longer-term cultural controls will need to be considered. For now, however, an early post-em application of Trooper (flufenacet + pendimethalin) at 2-litres/ha + Fence (flufenacet) at 0.25-litres/ha + Xerton (ethofumesate) at 0.6-litres/ha + Remix to keep the active ingredients in the top couple of centimetres of soil where they do most good, has done a fantastic job in trials and commercial situations. Grassland growers who have not yet controlled perennial grassland weeds such as docks, thistles and nettles should consider doing so. These weeds will be returning nutrients to the roots in preparation for winter, so will translocate herbicide as well, improving control. Doxstar (fluroxypyr + triclopyr) will do a good job where docks are the main problem. For additional thistle and nettle control, use Pas Tor (clopyralid + fluroxypyr + triclopyr), or Forefront T (aminopyralid + triclopyr) + Companion Gold on grazing. I’ll add Companion Gold in each case to improve efficacy. Esme Shephard is an agronomist with Agrovista, based in Wiltshire (esme.shephard@ ■

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Farmers Guide October 2017  

Farmers Guide Magazine October 2017 Issue