Spotlight on Grass Weeds in Wheat and Barley: Expert Tips to Maximise Control

06 March 2025, UK: For growers of cereal crops in the UK, controlling grass weeds like blackgrass, ryegrass and wild oats can be a constant battle. Previously confined to specific areas of the country, they have relentlessly spread in recent years, creating additional workload and frustration as well as yield losses. Syngenta’s Field Technical Manager Georgie Young discusses some of the biggest grass weed management challenges facing growers and shares some expert tips to maximise control. 

Blackgrass is most commonly found in cultivated land in South-East England, though it has spread North and West across the UK. Ryegrass, too, is present on noticeably more farms, having spread from areas like Yorkshire and Essex. For growers of wheat and barley crops, the threat is very real. Grass weeds can cause massive yield losses as they compete with crops for water, nutrients, light, and space. They also produce so much seed that even a small population can get out of control very rapidly. Only 12 blackgrass plants/m² can cause a 5% yield loss, and with wild oats its ability to produce tillers means only 5 plants/m² can reduce yield by 5%. Grass weeds can also generate issues with harvest. 

When you’ve got lots of green grass weed stalks within a crop, it can lodge the crop and then combining becomes difficult and time-consuming. That means you lose yield and quality further, not just through competition but through the lodging impact as well.

Says Georgie. 

The biggest weed management challenges growers face 

The biggest grass weed management challenges facing growers are increasing problems of herbicide resistance coupled with trying to balance the need for long-term weed management and having to respond to seasonal conditions. There is evidence of blackgrass resistance on virtually all UK farms, and surveys in 2019 and 2021 suggested resistance in rye grass is increasing, particularly where production is mixed. 

Cultivation is another weed management strategy in the grower’s toolbox, but it’s seasonally dependent, and in the moment decisions can impact on overall weed control. 

Growers need to think about their cultivation strategy across the whole rotation. Sometimes, it’s about making quick decisions now to get crops into the ground which can be problematic in terms of the overall rotational weed control, but growers are in a challenging situation when drilling a crop or not has such a big influence on profitability. 

Adds Georgie. 

To maximise control of grass weeds, Georgie recommends an integrated strategy:

• Clean machinery down before moving onto another field to stop the spread of weeds. 
• Wait until there’s a flush of weeds before the crop is planted, then use glyphosate to get rid of them and reduce the population you’re planting in to. 
• Drill fields with known issues when you know you can apply a pre-emergence herbicide within 48 hours of drilling. Avoid wet and/or windy conditions. 
• Apply a post-emergence herbicide three weeks after the pre-emergence application to extend residual protection against weeds coming through in the main autumn germination period.
• When conditions warm up in the spring and plants start to grow, a well-timed and correctly applied contact herbicide application at the right rate will prevent weeds from competing further with the crop and damaging yield. 

Looking to the future 

Minimising seed return is key to effective weed management and Syngenta is looking at promising techniques for the future: 

There are techniques we are looking into which are becoming increasingly popular. For example, we’re sponsoring a PhD student who is looking at techniques such as cutting the heads off weeds before the crop then comes into ear, to see if you can reduce the amount of seed that’s returned by the weed.

Says Georgie. Growers in the here and now can minimise seed return by spraying off patches of weeds with glyphosate. Though this will depend on whether they feel this is financially viable. 

Depending on the wheat price, farmers may be more or less willing to do that, and sometimes it’s a tough decision to take the hit in a year where the wheat price is really good and spray off some of the crop, to benefit the weed burden for coming seasons. 

Adds Georgie. 

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