Technical
Dandelion, brome and annual meadow grass growing in a pavement. The loss of many active ingredients for use on hard surfaces makes the sole reliance on one mode of action more likely
Fleabane (conyza) resistance to glyphosate has been confirmed in Europe. This is a weed which is widespread in the UK, especially in urban areas and along railway lines
Resistance risks
• There are no reported cases of glyphosate resistance in the UK ‐ but the risk is real!
• Development of resistance in Europe is mainly due to repetitive or inappropriate practices:
- Over-reliance on the same herbicide i.e. glyphosate
- Not following label recommendations
- No or limited Integrated Weed Management strategies
• Eradication of resistance once detected is not possible
required for the toughest weeds present at the time of application. This is normally 1800g ai/ha (e.g. 5l/ha of Roundup ProActive) for perennial weeds, which will also control annuals and grass weeds. Further dose reductions should be avoided since they can encourage a shift to tougher weed species and more difficult biotypes.
2. Growth stage. Ensure the treatment is made at the correct weed growth stage. Timing of the application can be critical in particular for perennial weeds and, where glyphosate is used continually, it may be necessary to alter the timing of application each year to prevent a shift to species which are less susceptible at the usual application timing.
In particular, application during the period of rapid stem extension growth (as the flowering stem is growing away from the foliage) in both grasses and broad‐leaved weeds can lead to poor control.
For example, Canadian Fleabane (Conyza canadensis) should be treated at the rosette stage in the spring for maximum effect. It is much less susceptible at stem extension in June/July ahead of flowering in August/September. Similarly, Couch (Elymus repens) is most susceptible when there is plenty of fresh active growth but not when leaves first emerge.
3. Any pesticide or herbicide should not be overused and should be managed sustainably. The use of other active ingredients and non‐chemical methods of weed control should be incorporated into an Integrated Weed Management Programme where appropriate, so there is not sole reliance on one mode of action.
Following the loss of approval for many residual herbicides, especially on hard surfaces, this has become more difficult, but should be considered where possible. e.g residuals, such as flazasulfuron, diflufenican or sulfosulfuron, can all be used in a mixture with glyphosate on plant‐free areas with permeable surfaces, but only sulfosulfuron on hard surfaces.
4. Good spraying practice should always be followed to attain effective weed control:
• Spray equipment must be checked and calibrated regularly to ensure dose rate is accurate
• Choose nozzles/equipment to maximise coverage of the weeds and minimise spray drift
• Apply only under appropriate weather conditions and choose a formulation which performs well under a wide range of conditions, like Roundup ProActive or Roundup ProVantage
Ensure:
‐ weeds are not stressed due to high temperatures, frost, drought or water logging
Good practice is essential, including checking and calibrating spray equipment to ensure dose rate is accurate, and choosing nozzles to maximise coverage of the weeds and minimise spray drift
134 I PC JUNE/JULY 2018
‐ no rain falls during application or within four‐six hours after application
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