Weed control advice for East Anglian growers heading into winter

Article overview

Current situation (21 October)

There is a divide across East Anglia in how badly affected drilling has been by wet weather through the end of September and October.

In east Norfolk and east Suffolk, after a long period of dry, the rain was almost helpful even though it stopped drilling, in encouraging germination and, where crops are still to be drilled, a flush of grassweeds.

But for the majority of Norfolk, Suffolk and Cambridgeshire there has been a lot of rain, and it’s made making progress with drilling difficult. Growers have been able to drill on sandy lighter soils, but have had to be very choosy on heavier soils.

The western parts of East Anglia, heading towards Bedfordshire, it’s been extremely wet and very few fields have been drilled on the predominantly heavier soils.

I’d estimate that currently less than half of the wheat across the region has been drilled.

Rachel’s agronomy tips for November and into winter

1) Three scenarios to consider for weed control in wheat

Most fields will likely fall into one of the following three scenarios:

Drilling date was as intended, pre-em herbicides applied, and now waiting for a top-up residual for difficult grassweeds
Drilled in October, but no chance to apply pre-em either because of weather or drilling workload, so now looking at a late residual herbicide peri- or post-emergence
Still to be drilled – hoping for November or December – weed control to be decided

Options for top-up residual herbicides will depend to some extent on what was applied as a pre-emergence. If Liberator (flufenacet + diflufenican) + Proclus (aclonifen) was used as a pre-emergence that leaves the opportunity to use a cinmethylin product at early post-emergence.

Alternatively, if cinmethylin or any non-Bayer option was the choice at pre-emergence, then there is an option to follow up with Liberator or one of the metribuzin-containing products (Alternator Met, Octavian Met, Cadou Met), which are formulated with flufenacet and diflufenican.

The metribuzin brings another mode of action, which for grassweeds such as Italian ryegrass is very useful, plus has a little bit of contact activity, so for post-emergence use where some weeds will inevitably germinate as well as the crop, it should give a little more control. It also has a slightly wider window of activity against broadleaf weeds with both diflufenican and metribuzin working together for weeds such as groundsel and bur chervil.

Those products are also the main ones to consider where pre-emergence applications were missed for any reason, and the crop has now emerged. In this case, tank mixing additional residuals, such as pendimethalin, prosulfocarb or tri-allate is worth considering, especially where there are higher populations of grassweeds. Remember, Proclus isn’t an option as it can only be used as a pre-emergence product.

There could also be a case for considering tank mixing Atlantis OD (mesosulfuron + iodosulfuron) with a Liberator or metribuzin product, if there has been a large flush of grassweeds, which residuals alone will struggle to control.

Control is often better from mesosulfuron-containing products from an autumn application when grassweed growth stages are smaller than from a spring application, especially if that is delayed into late March or beyond. But remember this will use up your one and only hit of a grassweed-active sulfonylurea in the crop.

The last scenario is where wheat is being drilled in November or December. Given the weather this autumn, it might not be easy to achieve decent seedbed quality with later drilled crops, which can have an impact on crop safety with residual herbicides.

Where seed has been covered by at least 32mm of soil, drilling depth is relatively even and slots closed, then using a pre-emergence herbicide, such as Liberator + Proclus will make sense as it is a lot easier to control grassweeds in the autumn than leaving them until the spring. But it is more difficult decision if seedbed quality is poor. Delaying spraying until the crop has emerged can be safer for the crop, but there’s a chance you might not get back before the spring, and efficacy might be compromised.

That makes it a difficult decision and one you might not, in hindsight, get right every time. My preference in most situations is to look at the forecast but try to go as soon after drilling as you can to maximise weed control of the ground you can hit.

2) Can you justify an oilseed rape fungicide this autumn?

As ever with oilseed rape now, it’s a mixed picture with some crops failing in the eastern part of the region because of a lack of rain in August and early September. Other crops established very well and quite forward. These ones should justify investment over the season.

In early drilled crops light leaf spot will be higher risk, while the rainfall in the last month will also increase risk from Phoma. However, most oilseed rape varieties have decent resistance to both diseases.

That makes walking fields and monitoring for disease important. The ‘put some leaves in a plastic bag and incubate somewhere warm for a couple of days test’ is helpful to accelerate any symptoms to assess risk.

Where disease is being found, a spray of Proline (prothioconazole) or Aviator (bixafen + prothioconazole) will be justified.

3) When to terminate cover crops?

Looking ahead to later in winter and the highly debated how to terminate over-wintered cover crops, and when to do it, questions will become topical again.

Typically, the most effective way to terminate is through a glyphosate application. Grazing or rolling on a frost can be useful to help get that process started, but will likely need a glyphosate application to finish the job, or you can just use glyphosate.

For timing, I’d work back from your intended spring crop drilling date, and look to apply glyphosate at least four weeks earlier to avoid any unwanted impact on the following cash crop.

One of the main things to consider when applying glyphosate is the species mix in the cover crop. Species with big vegetative systems or root stocks, like stubble turnips or vetches, will require higher doses to translocate through the plant for total kill, than species like black oats which are easier.

Remember to also take into account growth stage when choosing rates and that the plants need to be actively growing to take up and move the glyphosate around the plant.

4) Sprayer maintenance

It should be engrained, but don’t forget to follow the basic best practice advice for sprayer maintenance after the last autumn sprays have been applied. Clean out sprayers properly, use antifreeze as necessary to make sure there are no unwanted surprises in the spring, and get on top of any maintenance required.

In the spring, run some water through to check seals, pressure gauges, etc., are still working – the last thing you need on the first good spray day is finding an issue with the sprayer.

Liberator® contains flufenacet and diflufenican. Proclus® contains aclonifen. Atlantis® OD contains mesosulfuron and iodosulfuron. Alternator Met® contains metribuzin, flufenacet and diflufenican. Octavian Met® contains metribuzin, flufenacet and diflufenican. Cadou Met® contains metribuzin, flufenacet and diflufenican. Proline® contains prothioconazole. Aviator® contains bixafen and prothioconazole. Liberator, Proclus, Atlantis, Alternator met, Octavian Met, Cadou Met, Proline and Aviator are registered trademarks of Bayer. Use plant protection products safely. Always read the label and product information before use. Pay attention to the risk indications and follow the safety precautions on the label. For further information, including contact details, visit www.cropscience.bayer.co.uk or call 0808 1969522. © Bayer CropScience Limited 2024. 