Early season weed and disease control for growers in the Midlands

1) Assess weed size to determine spring herbicide strategy in wheat

Grassweeds like black-grass and Italian ryegrass are mostly only just starting to emerge through previous treatments. Where this is the case in later drilled crops there could still be a place for using a residual herbicide top up, such as one of the metribuzin-containing products. Adding the metribuzin adds a little bit of contact activity to the residual action from flufenacet and diflufenican in these products.

Where grassweeds are more established and have reached two-leaf stage or bigger, the choice switches to a pure contact acting herbicide, usually containing mesosulfuron. Where brome is among the weed targets then you can use Pacifica® Plus at 0.5 Kg/ha, while Atlantis® Star can also be used to apply 0.333 Kg/ha without the brome target restriction.

Keep an eye out for bright sunny days when making mesosulfuron applications – we did some light intensity work with the University of Nottingham looking at brome and Italian ryegrass control. That data suggests that if you apply in higher light intensity (replicating a bright sunny day), even if it is cold – the university work was conducted at 6C – there was an increase in efficacy.

2) Best practice with glyphosate sprays crucial

Recent finding of Italian ryegrass population that is resistant to glyphosate applications highlights how important application technique, good practice and optimum doses are for both maximising efficacy and minimising the risk of resistance development.

Unfortunately, in the midst of busy periods or where the weather goes against us, that’s not always followed as closely as it could be. Last year, we saw some sub-optimal efficacy from glyphosate sprays where it was applied to stressed plants (not) growing in waterlogged, anaerobic soils, or at lower-than-optimum rates when doses didn’t match target species size.

It's also important to avoid spraying grassweeds during stem extension as Roundup® is less effective during that period.

And definitely avoid spraying glyphosate on any survivors from a previous application – use cultivation or another alternative to remove them.

3) Target rusts at T0 in wheat

After last season, where brown rust was the most threatening disease, there’s definitely a need to monitor for it again this spring. While the winter weather hasn’t been quite so mild as last winter, we haven’t had the persistent -5C nights to kill it off. Many Recommended List brown rust resistance scores are not above a 6, and with most cultivation systems based on no- or minimum tillage there’s potential for quite a lot of over-wintered inoculum.

When you look at the disease cycle of brown rust, it’s much quicker than both yellow rust and brown rust. Last year, in the period from T0 to T3, there were seven plus cycles of brown rust infection compared with five for yellow rust and two or three for Septoria.

Given all of that, it will be important to keep monitoring for it, and probably apply a T0, as it represents a really good opportunity to dampen risk for the rest of the season.

Earlier drilled crops will be at more risk from brown rust, while later drilled ones have higher susceptibility to yellow rust. Both can be controlled using a combination of azole and strobilurin, such as Firefly® or tebuconazole plus azoxystrobin.

Having visited our Bayer Field Days site at Walpole recently, there was also Septoria in many varieties, despite an early November drilling date, so this will also need monitoring.

4) Remember T1 is the most important spray in winter barley

Up to 60% of the response to fungicides comes from not T2 but the T1 timing in winter barley – the opposite of what is well-known in winter wheat where protecting the flag leaf is critical.

Barley is sink-limited, meaning its yield potential is determined early in the season. Effectively it’s all about maximising grains per square metre, and achieving that results from maximising viable tillers during March and early April. Any disease infections during this period can cause the plant to abort tillers, reducing yield potential.

With reports of net blotch and brown rust already in crops this spring, a broad-spectrum proven fungicide, such as Ascra® Xpro® or Siltra® Xpro® will help provide that protection. The combination of prothioconazole plus SDHI in both will also give good control of Rhynchosporium and some control of mildew.

5) Monitor for light leaf spot in unprotected oilseed rape crops

Pigeons have become the main threat to the relatively limited area of oilseed rape in the East Midlands, but where that threat has been overcome, keep an eye on light leaf spot, especially where crops haven’t received a fungicide as yet.

It’s not the easiest disease to spot in early stages of infection, so leave some leaves in a plastic bag in a warm place for a few days to help speed up visual symptoms and treat with Proline® or Aviator® Xpro® where appropriate.

6) Tips if you’re drilling Conviso® Smart sugar beet varieties

Earlier sugar beet drilling should be on the cards this season with no one waiting for seed deliveries delayed by neonicotinoid seed treatment.

If you’ve chosen to grow Conviso® Smart herbicide tolerant sugar beet this season then, just as with glyphosate, there are some key stewardship requirements to follow to make sure this is a technology you can use for the long term.

These include not mixing Conviso® Smart and conventional variety seed in the drill, and only sowing whole fields with Conviso® Smart varieties. Ensure drills are completely clear of conventional seed when drilling Conviso® Smart – you can tell which is which by the purple inner to the pellet.

Only plant areas that can be harvested – planting areas where a harvester cannot lift increases the risk of groundkeepers in the following crop – and mark fields either physically in the field or on mapping software accessible to your team so everyone knows which fields are which.

With either system, using a pre-emergence herbicide is worth considering – it gives a bit more flexibility over timing of post-emergence sprays.

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Ascra® Xpro® contains bixafen, fluopyram and prothioconazole. Atlantis® Star contains iodosulfuron-methyl-sodium, mesosulfuron-methyl and thiencarbazone-methyl. Aviator® contains bixafen and prothioconazole. Firefly® contains fluoxastrobin and prothioconazole. Pacifica® Plus contains amidosulfuron, iodosulfuron-methyl-sodium and mesosulfuron-methyl. Proline® contains prothioconazole. Roundup® contains glyphosate. Siltra® Xpro® contains bixafen and prothioconazole.

Ascra, Atlantis, Aviator, Firefly, Pacifica, Proline, Roundup, Siltra, 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