Early season weed and disease control advice for growers in the west

1) Assess weed control needs carefully

Not surprisingly there are various different scenarios for weed control in wheat you could be facing this spring. There are some crops that had a decent residual herbicide programme and currently look clean, others that were drilled late and have fewer weeds more because of drilling date, while there are also crops drilled early and had no residual chemistry in the autumn and it will be contact herbicides all the way now.

There’s still a place for applying a residual herbicide during March, where what’s emerged is still small and / or you’re expecting more grassweeds to emerge. Our range of metribuzin-containing products, Alternator® Met, Octavian® Met or Cadou® Met, fill this need, up to GS25 of the crop, with the metribuzin also giving a small amount of contact activity to back up the residual activity from flufenacet and diflufenican.

Where out and out contact activity is required with grassweeds having two or more leaves, then you’re more down the route of a mesosulfuron-containing product, such as Atlantis® Star where you can apply 15g/ha of mesosulfuron from 1 February. Where brome is a target, Pacifica® Plus is a useful alternative choice at the 0.5kg rate from 1 March.

You may also need to add a specific contact herbicide to help with emerged broadleaf weeds but check labels carefully. If you are mixing two sulfonylurea herbicides, it needs to be on the label of at least one of the products, and there may be some following crop restrictions.

And then there will be some in the middle with both emerged and emerging weeds where a mixture of contact and residual might be the best option.

2) Rust watch for T0 sprays in wheat

T0 sprays – around GS30 – in wheat are usually trying to control yellow rust, but off the back of last year’s epidemic, you probably need to consider brown rust as well.

The extent and earliness of brown rust is usually determined by winter temperatures, and while it hasn’t been as warm as last winter, March temperatures will also have an influence, plus the level of inoculum carryover from last year, so keep monitoring crops.

Don’t assume the actives you use for yellow rust will have the same level of efficacy for brown rust – generally and it is a bit of a broad brush statement, azole fungicides work better on yellow rust and strobilurins on brown rust. SDHIs are more variable depending on which one you’re using, although you’re unlikely to use one at T0.

Strobilurins are restricted to a maximum of two applications in wheat crops, so make sure you take that into consideration. It also has to be partnered with another product with an alternative mode of action that has a similar level of efficacy on that pathogen – that applies to rust as well as Septoria, albeit it is almost certainly the latter which is the reason it is on the label.

The other thing to remember is dose gives you the efficacy. A product might have good efficacy on paper, but it won’t give the efficacy you’re expecting if you use too lower a dose.

3) Saving for an expensive spray at T2 in winter barley is false economy

I’m hearing conversations suggesting some agronomists and growers might be thinking about cutting spend at T1 in winter barley to apply an expensive product at T2. I think that would be a mistake as yield in winter barley comes from grains per square metre, and that’s all about tiller retention.

Early season sprays in winter barley have a more direct correlation with yield than some might perceive. Timing is important – T1 in winter barley is earlier than in wheat at GS30/31. This is when any disease infections can cause tillers to abort and is typically around the last week of March or first week of April.

If you’re also thinking about applying a T0, that should be two to three weeks earlier in mid-March but is less important unless you have significant infections that are already causing the plant to abort tillers.

Our options for T1 sprays are Ascra® Xpro® or Siltra® Xpro®, which both give proven broad spectrum disease control.

4) Follow best practice glyphosate applications

With the finding of three glyphosate resistant populations of Italian ryegrass, it’s important to follow best practice to get the best from Roundup® and minimise the risk of further resistance development.

That means a good glyphosate formulation – Roundup® branded – at the right dose for the right species. Controlling some cover crops species might require 1440g a.s/ha, for example, while tillering grassweeds should be a minimum of 1080g a.s/ha.

Growing conditions are important. Spraying weeds (not) growing in wet anaerobic soils or grassweeds going through stem extension are not conducive to glyphosate working well.

If there are any survivors from glyphosate applications, take these out with cultivation or another alternative method rather than re-applying glyphosate. And if you think you have a questionable result on a plant, don’t let the plant shed seed.

4) Monitor for light leaf spot in oilseed rape

Light leaf spot will keep cycling in oilseed rape crops unless it is treated, and it’s important to prevent it from reaching the pods where it can be extremely yield damaging.

Two actives are really good against it in March – prothioconazole and tebuconazole. One gives growth regulatory effects, the other doesn’t, so if you want to shorten the crop, then you’ll need a good dose of tebuconazole. Prothioconazole won’t have those effects.

5) Consider Velum® Prime as a nematicide

It’s not as good a nematicide as Nemathorin, but there are places where Velum® Prime might fit, either used alone where there are low potato cyst nematode populations or in combination with either half or full rate Nemathorin.

If you are thinking of using it, it can be applied in one of two ways to suit your system – either in-furrow or as an overall spray which is then incorporated. There’s no difference in efficacy between the two methods.

-----

Alternator® Met, Cadou®Met and Octavian® Met contain diflufenican, flufenacet and metribuzin. Ascra® Xpro® contains bixafen, fluopyram and prothioconazole. Atlantis® Star contains iodosulfuron-methyl-sodium, mesosulfuron-methyl and thiencarbazone-methyl. Nemathorin contains fosthiazate. Pacifica® Plus contains amidosulfuron, iodosulfuron-methyl-sodium and mesosulfuron-methyl. Roundup® contains glyphosate. Siltra® Xpro® contains bixafen and prothioconazole. Velum® Prime contains fluopyram.

Alternator, Ascra, Atlantis, Aviator, Cadou, Octavian, Pacifica, Roundup, Siltra, Velum and Xpro are registered Trademarks of Bayer. All other brand names used are Trademarks of other manufacturers in which proprietary rights may exist. 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 2025