Arable News

  • Written by: Farmers Guide
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Agronomy Update Oct 2018

A simple technique to improve spray coverage will help boost pre-em black-grass control this autumn, says Agrovista agronomist Rob Sheets.

Achieving an even coverage of the seedbed when applying pre-emergence herbicides is vital to ensure the chemistry works as effectively as possible.

One of the most important factors governing this is the number of droplets produced by the nozzle. We need to paint the soil evenly and, within reason, the more droplets we can produce, the more effectively we can do that.

Using twin caps fitted to a single spray line enables us to double the number of nozzles, and therefore droplets, for the same water volume, and I would recommend a minimum of 200-litres/ha when spraying black-grass. 

Nozzle know-how

The twin caps have back-to-back nozzle apertures. Billericay twin caps are already angled forward and down, so two VP 80 flat fans can be used. Hypro Twincaps are inclined 30 degrees forwards and backwards, but fitting a Defy 3D (80-degree) nozzle to the rear-facing aperture produces a near-vertical fan.

Using twin caps mimics a twin-line set up, which has given excellent results in our trials. On heavily infested black-grass land in Northamptonshire, for example, applying full-rate diflufenican and flufenacet in 200-litres/ha of spray at 3 bar through twin lines fitted with blue 80-03 flat fan nozzles, carried 50cm above the ground, gave 90 per cent control. A single line set up of 80-04 flat fans, alternating forwards and backwards, gave just 80 per cent control. 

It really is worth spending the time to get application right. Too many people look to cover the ground quickly using around 100-litres of water/ha applied through low-drift nozzles so they can keep going in marginal conditions, but at what cost?

Several of my growers have now adopted the twin cap technique, and they believe they are seeing a difference.

Whatever technique is being used to apply pre-ems, I’ll be recommending Remix, a long-chain hydrocarbon application aid that reduces spray drift and produces a more consistent droplet size. It also keeps the chemistry in the surface layer for longer to optimise weed control and reduce seedling damage.

Significant uplift

Extensive trials over the past 10 years have shown Remix increases black-grass control from a typical pre-em stack by 11 per cent, a very significant uplift, for a few £/ha.

Remix consistently outperforms competitor products. In the season just gone, for example, Remix and a product which claims to be the same were applied in a tank mix with pre-em Liberator (diflufenican + flufenacet) at 200-litres/ha through flat fan 04 nozzles, at three sites in the East of England.

Remix gave an average 7 per cent uplift in black-grass control, and maintained a 2 per cent lead overall under four different post-emergence follow-up treatments. That could make the difference between achieving the 98 per cent control we need to reduce the black-grass burden, or not.

I’ll also be keeping a close eye on grass weed control in oilseed rape. A combination of low-dormancy black-grass and the reduced cultivations when establishing OSR crop this summer means there are likely to be a lot of grass-weeds near the surface that will be germinating readily.

As usual I’ll be starting early, using clethodim (as in Centurion Max) by the end of September, before following up with carbetamide (Crawler) in bad situations in October and propyzamide (Kerb) in all fields when conditions are cool enough to optimise activity. We cannot afford to wait and expect Kerb to kill large, well-tillered black-grass plants – that is a recipe for disaster.

Centurion Max can no longer be applied on any variety of OSR after 15th October. We must also observe stewardship requirements on carbetamide and propyzamide if we want to preserve them for future use. Please do check all requirements carefully before application. 

Rob Sheets is an agronomist with Agrovista, based on the Northamptonshire/Cambridgeshire border ([email protected])


 

Replacements for failed oilseed rape crops and maximising early black-grass control are just two topics that are keeping Agrovista agronomist Esme Shephard occupied this month.

Cabbage stem flea beetle has been widespread across my area of Wiltshire and neighbouring counties. Most fields have been hit hard, and some crops will need to be replaced.

The good news is that crops sown into moisture, notably those that were direct drilled, had 2–4 leaves by mid September and are growing away well.

Those established using more traditional cultivations have struggled, and have been sitting at the cotyledon stage through this dry weather, which has also been ideal for flea beetles. Some crops have been sprayed with pyrethroids, but with up to 60 per cent of flea beetles now said to be resistant, the effect is limited.

Most crops will pull through, but growers faced with a few skeletal remains will need to rethink. The most obvious replacement is winter or spring beans to maintain the break from cereals. These may not be as profitable as the crop they are replacing, but costed out over the rotation the decision is very likely to stack up.

Growers who have applied chemicals, mostly pre-emergence at this stage, should beware of falling foul of any following crop restrictions as described on the label.

For example, where clomazone has been used, manufacturers advise that winter beans cannot be sown until 6 weeks after application and soils must be ploughed to 25cm. The same restrictions apply to winter cereals.

Some pre-ems are also subject to statutory restrictions, while others may offer some flexibility at growers’ own risk. Please do check the label before ordering a replacement crop.  

Freshly shed black-grass seed is said to have low dormancy this year, so using the most effective pre-emergence chemistry will be even more important to achieve the best kill. We know from many trials over many years, as well as field experience, that tri-allate granules (Avadex Excel) deliver up to 30 per cent additional activity when added to the pre-em programme. 

Liquid formulation

However, Avadex Factor, the liquid formulation introduced last year, does not contain as much active at the full rate, so delivers less additional control. For that reason I’ll stick with granules, provided growers have access to an applicator, although Factor could still be useful for those that don’t.

Whichever version is used, the aim should be to drill, roll and apply Avadex within 48 hours. The chemical (and other pre-ems) requires moisture to work, so a rethink may be required where soils are bone dry, perhaps even delaying drilling until conditions improve, rather than risking a massive flush that proves impossible to control in the growing crop. 

If post-emergence control is required in the following few weeks, I’ll recommend Xerton (ethofumesate) at 0.6-litres/ha in addition to flufenacet, plus adjuvant Remix.

Despite the long dry summer, slugs can be found and will need monitoring. If control is needed, for those of you who aren’t using solely ferric phosphate, it is important to remember the stewardship rules that came in last year for metaldehyde. These include leaving a 10m margin around any field boundary (including trees in the middle of a field) and utilising integrated pest management, such as rolling and creating fine seedbeds.

Esme Shephard is an agronomist with Agrovista, based in Wiltshire ([email protected])


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