Protecting OSR "Starts Here!" with pre- and post-emergence herbicides
Pre-emergence protection
For those crops of oilseed rape yet to be established, the most effective way of ensuring seedlings are able to establish unhindered by weed competition is to apply a timely pre-emergence herbicide.
By reducing the weed burden before crops have emerged out of the ground, there will be less pressure on subsequent post-emergence treatments: without the application of a pre-emergence treatment there’s a danger weeds could grow too large to be controlled by post-emergence herbicides. There is also the added danger that a well-developed crop canopy could reduce the efficacy of post-emergence treatments, especially where rate and timing restrictions result in long delays between the emergence of early drilled crops and post-emergence actives being applied.
A pre-emergence herbicide should therefore be applied, especially where good crop establishment is expected – for example where Cabbage Stem Flea Beetle (CSFB) populations aren’t expected to pose a significant threat to OSR survival (either due to the earliness of drilling or geographical location).
A combination of mutually beneficial chemistries should be used throughout the OSR weed control programme to spread the risk of herbicide resistance and to ‘power up’ the overall efficacy of the combined pre- and post-emergence applications.
“Yield loss from poor broad-leaved weed control can range from 3% up to 73% depending on the vigour of the crop… this does not take into account the contamination of the harvested crop with weed seed which can reduce the marketability of the sample.” “The mean yield response to (pre-emergence and early post-emergence) herbicides over three years was 0.94 t/ha or 41%.”
New approaches to weed control in oilseed rape. HGCA, Project Report No. 530 (April 2015)
Start with SULTAN
SULTAN® 50 SC (500g/l metazachlor) is the ideal building block for early weed control in oilseed rape: it provides cost-effective control of a wide range of weeds including mayweeds, chickweed, red-dead nettle, speedwell and annual meadow grass. The only significant weeds not on label for metazachlor are cleavers and poppies, but these can easily be controlled will the addition of clomazone and quinmerac.
To protect against black-grass, it is important to apply SULTAN® 50 SC as soon as possible after drilling has been completed and to plan complementary post-emergence treatments to control any later emerging black-grass plants. Using metazachlor at the pre-emergence timing also helps in anti-resistance strategies for black-grass control: metazachlor acts as a holding treatment before subsequent clethodim treatments are applied after the crop has reached GS14. This can then be followed by a third treatment of propyzamide which should be applied when soil temperatures have fallen to 10oC. With all three actives used in sequence, a different mode of action will be in place to protect the crop throughout the entire black-grass germination window.
Best practice pre-emergence advice
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Apply SULTAN® 50 SC prior to weeds germinating. Failing this, apply at the early post-emergence timing (up to four leaves of the crop) to enable it to be taken up by the young roots of weeds.
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SULTAN® 50 SC doesn’t require much moisture to be activated, so apply even if conditions are dry.
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Kickstart black-grass control by applying 750g or more of metazachlor (1.5 L Sultan 50 SC) at the pre-emergence timing.
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In situations where broad-leaved weeds such as chickweed, cleavers and hedge mustard are a problem, include BLANCO™ (360 g/l clomazone) at the pre-emergence timing.
THINK WATER – STEWARDSHIP GUIDELINES
Stewardship guidelines apply to SULTAN and LEGION: on drained land avoid applying after 30th September and do not apply after 15th October.
For more information, visit the ADAMA UK website or click on the product links above. Alternatively, visit https://voluntaryinitiative.org.uk/schemes/stewardship/think-water/
Post-emergence OSR options
If pre-emergence herbicide treatments are hampered by poor conditions or if the seedbed was cloddy, SULTAN® 50 SC and LEGION® can also be used as early post-emergence treatments (up to the crop’s four-leaf stage, GS12-14, and before the end of January in the year of harvest).
Beyond the early post-emergence window, a selection of different post-emergence active ingredients and modes of action should be used to reduce the risk of weeds becoming resistant to any individual active ingredient.
In addition to protecting crops from yield robbing weeds, ADAMA’s range of post-emergence herbicides have also been shown to have little or no effect on the most used companion cropping species, buckwheat, which more and more growers are turning to in an effort to reduce the influx of CSFB.
Fight weeds with FALCON and FOX
FALCON® (100 g/l propaquizafop) is incredibly good at controlling volunteer cereals in a wide range of crops including winter oilseed rape and is also useful against annual meadow grass up to three leaves. Reduced rates can be used for volunteer cereals with the dose dependent on the crop species and growth stage, with accurate timing of application critical to efficacy.
FOX® (480 g/l bifenox) is recommended for the post-emergence control of a wide range of broad-leaved weeds in winter oilseed rape as it delivers good control of field pansy, black-bindweed, charlock, red dead nettle and speedwell species.
Using crop competition to control weeds
In addition to using the pre- and post-emergence herbicide options listed above, OSR growers should also focus on maximising the crop’s competitiveness as a means of managing weeds: in fields with a high weed burden, or where volunteer cereals are a known issue, maximising the crop’s competitiveness can be as important as the herbicide strategy itself, not just in the crop’s early growth phases, but throughout the season when other stresses such as drought, waterlogging or winged pests might be a factor.
The starting point for any such strategy is to ensure the crop establishes well so that it can grow away quickly. This can be encouraged through the following agronomic practices:
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Optimise seed rate: sow at an appropriate seed rate to ensure the OSR crop forms a dense canopy which can suppress weed growth by limiting the availability of light and space.
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Timely drilling: drill OSR in conditions that favour rapid germination to give the crop a head start over weeds. This is particularly important when using pre-emergence herbicides as it enables the crop to take advantage of the reduced weed competition.
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Nutrient management: support vigorous crop establishment and enhance its competitive edge by providing adequate nutrients during the early stages of the crop’s development.
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Stay alert for slugs
As well as getting new crops of OSR off to a good start by controlling weeds at the pre- and post-emergence timings, it’s important not to forget about the ever-present threat of slugs, especially as numbers could remain high despite the summer’s drought. ADAMA’s technical manager, David Griffiths, explains more.
Despite the summer’s hot and dry conditions, the potential for slugs to decimate emerging crops is still significant. This is because, although slugs need moisture to remain active, they are exceptionally well adapted to surviving adverse conditions. Therefore, as soon as wetter weather returns, they will start looking for fresh seedlings to feed on with any damage sustained at emergence having the potential for entire plants to be lost.
As a result, the timely and accurate application of good quality slug pellets is critical to ensuring crops remain protected, even after the summer drought.
Growers are therefore urged to regularly monitor for slug activity and to be prepared to protect vulnerable young crops as soon as slugs have been observed. But slug pellets shouldn’t be applied immediately prior to heavy rainfall as this can cause poorer quality products to degrade quickly. Regular slug counts, along with close interrogation of the weather forecast, should therefore be a priority, with spreaders calibrated and ready to be deployed as soon as slugs have been seen and a period of favourable, settled weather prevails.
Size matters
The size, weight, shape and consistency of slug pellets is vital to application accuracy, as is ensuring spreading equipment is properly set up and operated at a sensible forward operating speed of around 12kph.
Only the highest quality pellets will achieve consistent and accurate spread patterns, with ADAMA’s FERRABAIT® (1% elemental iron) and Gusto® IRON (2.94% ferric phosphate) pellets manufactured to strict tolerances to ensure they match their 2.5mm by 2.0mm size specification. This ensures a consistent spread pattern and an optimal number of baiting points of 40-50 pellets per m2 when applied at typical field rates
Both brands of slug pellet also offer improved longevity in wet conditions and are characterised by their bright blue colour which makes them easily visible in seedbeds so that growers can quickly assess when a second application is required. They also provide fast-acting protection against crop damage by suppressing slugs’ appetites as soon as they are ingested and offer class-leading durability and palatability thanks to ADAMA’s ‘Desidro Technology’ manufacturing process which uses a two-stage drying process to ensure an ideal balance between pellet persistence in wet weather and palatability.
The Desidro manufacturing process also gives both products excellent mould-resistance, with independent trials showing that FERRABAIT® and Gusto® IRON pellets retain their shape, colour and palatability and remain mould-free for up to a week longer than other leading brands in wet conditions.
For more information about FERRABAIT® go to https://www.adama.com/uk/en/crop-protection/molluscicides/ferrabait
For more information about Gusto® IRON visit https://www.adama.com/uk/en/our-solutions/molluscicides/gusto-iron