Luke Bullock's June Agronomy Update: Tackling Grass Weeds Before They Take Control
As June arrives, grass weeds become one of the most visible and frustrating challenges in arable crops. Standing proudly above the canopy with seedheads waving in the wind, they are impossible to ignore and serve as a stark reminder of the ongoing battle growers face each season.
For many, grass weeds are a greater concern than drilling misses or backward crop patches. Their ability to compete with crops, reduce yields, and replenish the seedbank means they require a long-term, strategic approach rather than a quick fix.
Rotation Remains Key
One of the most effective tools in the fight against grass weeds is crop rotation. Introducing crops that are established and harvested at different times can help disrupt weed lifecycles and reduce population pressure.
Grass weeds tend to thrive in cereal-dominated rotations, where crop and weed growth patterns often align. By incorporating break crops, growers can create opportunities to target weeds at different stages of development and reduce their ability to establish and spread.
Different crops also provide access to different herbicide options. For example, propyzamide can be used effectively in oilseed rape but is unavailable in cereal crops. Having the opportunity to use alternative active ingredients at various points in the rotation broadens the range of control measures available and helps reduce reliance on a single chemistry.
Limited Chemical Options
Despite the benefits of rotational diversity, the reality is that economically viable break crops remain limited for many businesses. When all production costs are considered, maintaining profitable alternatives to cereals can be challenging.
Chemical control options within cereal crops are also increasingly restricted. Many growers are already utilising available break crops and associated herbicide programmes, while post-emergence control in cereals often delivers inconsistent results depending on weed species, resistance levels and growing conditions.
As a result, it is becoming increasingly important to assess whether herbicide investments are delivering an acceptable return and contributing to long-term grass weed management objectives.
Sterile Strips: A Practical Defence
Sterile strips offer a highly effective method of preventing grass weed ingress from field margins and headlands.
Applying glyphosate to a narrow strip of crop, typically less than one metre wide where the crop meets the headland, can significantly reduce the movement of species such as brome and ryegrass into the field. This can be achieved using a quad bike or utility vehicle fitted with a small spraying setup.
While chemical usage is minimal, the process does require time and commitment. However, where grass weed pressure is high, particularly around field boundaries, the benefits can outweigh the additional labour requirement.
Ideally, sterile strips should be established before grass weeds spread from headlands into the crop, making prevention far more effective than cure.
The Value of Hand Rogueing
Hand rogueing remains an effective option, particularly where infestations are small and localised. Removing individual plants before seed return can prevent future problems and help protect the effectiveness of existing control measures.
While practical for smaller populations, the approach becomes increasingly difficult and labour-intensive as infestations grow. Nevertheless, it remains a valuable tool within an integrated grass weed management strategy.
Knowing When to Draw the Line
In some situations, the most effective solution may be the most difficult one to make.
Where grass weed populations are exceptionally high, allowing plants to set seed can have significant long-term consequences for field productivity. In these cases, terminating heavily infested areas with glyphosate may be justified to prevent further seed return and reduce future pressure.
Although sacrificing part of a crop is never an easy decision, protecting the long-term viability of the field can sometimes outweigh the short-term loss.
Taking the Long View
There is no single solution to grass weed control. Success comes from combining multiple strategies over several seasons, including rotational planning, cultural controls, targeted herbicide use, sterile strips, hand rogueing and, where necessary, crop sacrifice.
As grass weeds continue to challenge arable production, those who focus on reducing seed return and managing populations for the future will be best placed to win the June grass weeds war.