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Effect of grazing management on creeping thistle & other injurious weeds & integration of grazing with weed control - BD1437

The results of recent monitoring suggest that injurious weeds are a widespread and increasing problem in grasslands within the Countryside Stewardship (CS) and Environmentally Sensitive Area (ESA) schemes. Creeping thistle is considered to be the most difficult species to control; ragwort and spear thistle are also problematical. Mechanical topping is often ineffective. Overall herbicide applications are not permitted and spot treatment is only practical for small or patchy infestations. Height-selective herbicide application (‘weed-wiping’) can be effective, but often gives incomplete control. Even after apparently effective control, by whatever means, weeds often re-invade in subsequent years.

Grazing management is known to have an important effect on the incidence of injurious weeds. Current advice is to: (a) avoid severe grazing in late winter and early spring since this may reduce competition from grasses and create gaps for colonisation; (b) maintain a dense sward by grazing to recommended sward heights during periods of vigorous herbage growth in late spring, and when young weed shoots might be eaten or damaged. Whilst practical experience suggests that this strategy can be effective, there is a lack of quantitative evidence on the effects of timing and severity of grazing. Further, it is not known how these effects interact with permissible weed control measures.

Main objective
The aim of this project is to develop and test Integrated Weed Management Systems (IWMS) for the control of creeping thistle and other injurious weeds which are practical, effective and ecologically sustainable in the long term.

Policy relevance
The control of designated noxious weed species is required under the Weeds Act of 1959. Practical, cost-effective and ecologically sustainable weed control measures are essential to the achievement of the key policy objectives of the CS and ESA schemes, together with the wider objectives of the UK Biodiversity Action Plan.

Intended use of results
The results of this project will underpin the revision and refinement of current guidelines for the control of injurious weeds in grasslands managed under the CS and ESA schemes. This study will provide important insights into the ecological processes controlling the invasion and spread of injurious weeds in grasslands. It will also provide an opportunity to examine the agronomic and ecological implications of weed control measures. This information will be of use to practitioners, scientific advisors and policy makers.
The overall aim of the project is to develop and test Integrated Weed Management Systems (IWMS) for the control of creeping thistle and other injurious weeds which will provide: (a) Long-term control of weeds through rapid reduction of population densities to acceptable levels, followed by maintenance of populations at these low densities; (b) Prevention of (re-)invasion and/or spread of low-density populations such that they create future problems. These systems will be practical, effective and ecologically sustainable in the longer term.

The specific objectives are:
1. To determine the effects of severity and timing of grazing on the growth and spread of weed species, particularly creeping thistle. Effects in following years and cumulative effects, will also be considered;
2. To determine the efficacy of weed control practices, including weed-wiping and cutting, and their interaction with grazing management;
3. To consider, by means of limited monitoring, any adverse impacts of weed control strategies on non-target flora and invertebrates;
4. To recommend weed control strategies suitable for use within agri-environment schemes, particularly Countryside Stewardship and the Environmentally Sensitive Areas.
Project Documents
Time-Scale and Cost
From: 2000

To: 2003

Cost: £330,000
Contractor / Funded Organisations
Institute of Grassland and Environment Research (IGER), Natural Environment Research Council
Agricultural Land              
Environmental Protection              
Fields of Study
Environmental Stewardship