Stacking and sequencing: A solution to grass weed management

Stacking and sequencing of selective herbicide products should offer solutions to grass weed management in autumn sown crops where Atlantis (mesosulfuron + iodosulfuron) is starting to struggle, says Ron Stobart of NIAB TAG.

According to recent research, you should be using products delivering a total of three to five active ingredients, either in mixtures or in sequence – and the two approaches aren’t mutually exclusive, he suggests.

The 40-trial research project, now nearing completion, is evaluating a range of products and approaches for blackgrass management in cereals and in oilseed rape. It also includes brome and annual meadowgrass management in cereals. While all of the blackgrass sites have exhibited some form of resistance, the spread of resistance to Atlantis has been apparent over recent seasons.

Early suggestions are that good control can be achieved using a range of chemistry in product mixtures, except where weed populations are high.

In winter wheat, for example, 95% of blackgrass heads at low to moderate levels – that’s about 10-15 plants/sq m, or fewer than 100 heads/sq m – could be adequately controlled without using Atlantis. The most effective programmes often included flufenacet (Crystal/Liberator) along with stacking and sequencing of a range of products.

Where higher blackgrass populations exist, a combination of chemical, rotational and agronomic methods may be needed, he warns. HGCA is funding work in these areas, but the focus of this project is grass weed herbicides.

“We’ve accepted that resistance development is getting worse, and there are no new active ingredients on the horizon, so we must preserve the few we have left. Within the next year, the work will confirm the best actives and approaches for grass weed control for a given range of situations.”

The number of effective active ingredients for grass weed control has been whittled down not just by increasing resistance, but also by registration issues. Isoproturon and trifluralin have already been withdrawn. The Water Framework Directive is prompting greater scrutiny of all actives detected in watercourses, he explains.

Herbicides such as propyzamide (Kerb) and carbetamide (Crawler) are key materials for blackgrass control in oilseed rape and are the only commonly used blackgrass herbicides with no resistance issues. They have been very effective in trials, particularly when used in November and in sequence with other appropriate residual herbicides. However, they commonly occur in watercourses so safeguarding their future is important for the continued production of oilseed rape, stresses Mr Stobart.

As a further approach, he is looking at even older chemistry with blackgrass activity, namely tri-allate (Avadex) and napropamide (Devrinol). These materials can be of use to support other pre-emergence residual materials such as metazachlor (Butisan S) and to develop strategies less dependent on the actives at most risk due to their movement to water.

Where other grass weeds are concerned, for example annual meadowgrass in cereals, that means materials such as flufenacet, prosulfocarb (Defy) and pendimethalin (Stomp). For brome in cereals, it includes tri-allate and flufenacet, although suitable ALS materials can deliver effective brome control in wheat.

“The project is all about effective and sustainable approaches to weed management. I believe the £165,000 spent on it will be saved in no time by highlighting the best herbicide strategies using the full range of materials at our disposal until new modes of action are introduced,” concludes Mr Stobart.

SUMMARY

Project no. 3341: New strategies to maintain autumn grass weed control in cereals and oilseed rape; NIAB TAG, SAC; from August 2007 to August 2011.

HGCA perspective:

• Grassweed control paramount to arable profitability

• Find sustainable and effective herbicide management strategies

• Review role of individual active ingredients in light of herbicide resistance and water pollution risks

• Firm up on best application timings

Project Progress available at www.hgca.com/weeds

Crops perspective:

With few active ingredients to turn to, it’s important to get the best from each and to prolong its usefulness in keeping grass weeds out of cereals and rape. This work should highlight the most reliable herbicides and when to use them to reduce the risk of yield loss and manage resistance development.

Catch up with previous pieces from our Research in Focus series by visiting our dedicated webpage.

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