Adjuvants and Autumn residual herbicides

Residual herbicides have remained an important part of autumn weed control programmes for growers, particularly when it comes to grassweeds such as blackgrass and ryegrass. However, even the most effective active ingredients rely on getting to the right places in order to perform well, if at all. 

Autumn weather has become increasingly unpredictable, so it is more important than ever that growers achieve consistent herbicide performance. Dry seedbeds can reduce herbicide movement into the upper soil layer where weeds germinate, while excessive rainfall can cause runoff, reducing efficacy. These changing and rapidly changing conditions mean growers need to do all they can to ensure herbicides meet their target.  

Unlike contact herbicides, residual products create a protective layer within the soil. As weed seeds germinate, emerging shoots or roots absorb the active ingredient. If this is going to happen effectively, herbicides need to be distributed evenly across the soil surface and remain there. Uneven coverage, spray drift or poor retention on soil will all reduce effective weed control, particularly if environmental conditions are challenging or inconsistent. 

Application quality has therefore become just as important as product choice. Factors such as nozzle selection, water volume, forward speed and weather conditions all influence how effectively a residual herbicide can perform. 

Adjuvants are designed to improve the physical performance of spray applications, helping maximise the effectiveness of any products they accompany. Rather than altering the herbicide, they improve how the spray behaves during application and once it reaches its intended target. 

When used with residual herbicides, suitable adjuvants can help improve spray coverage across the soil surface, increase adsorption to soil particles and reduce spray drift. Together, these effects help create a more consistent herbicide layer, supporting reliable weed control across a range of field conditions. Grassweed control is often determined by marginal gains. Even relatively small improvements in efficacy can translate into meaningful reductions in weed populations, helping protect crop yield and the longevity of valuable herbicide. 

Trial work has consistently shown that using an appropriate adjuvant within autumn residual programmes makes significant improvements. Across 18 blackgrass trials conducted between 2020 and 2026, the addition of Adhere increased control by an average of 4%, with positive responses recorded in 90% of trials. Further UK trials have also shown improvements in ryegrass control when used alongside both pre- and peri-emergence herbicide programmes. While 4% may appear modest, when multiplied across thousands of weeds per hectare, these incremental improvements can have a measurable impact on weed seed return and ROI.  

There is no single solution to grassweed management. Success comes from combining herbicide programmes and high-quality application techniques into an integrated strategy. As autumn drilling conditions continue to be changeable and challenging, ensuring every application performs to its full potential is increasingly important for growers. Selecting the right adjuvant alongside an appropriate residual herbicide programme is one simple step that can help maximise herbicide performance and give autumn crops the strongest possible start. Get in touch with your agronomise or the IntraCrop team for advice.