Brome in hyrid barley

Weeds have been a constraint on crop yield since agriculture evolved. Technical advances in herbicides and arable crop management, particularly since the 1940s, have improved the efficiency of weed control. Today, we are aware that major changes in common flora and fauna of the arable ecosystem are occurring, with population size and range contractions. From a statutory regulatory viewpoint, it is necessary to know what risks are posed to users and the environment by the use of pesticides. The observed effects in the environment indicate that risks caused by indirect effects of pesticides also need to be evaluated, to augment the traditional assessment of direct risk using toxicity and exposure. Current draft risk assessments for non-target plants address effects outside the crop. However, the indirect effects within crops must also be addressed, as they may be of greater significance. 

This project examines non-target effects of herbicides on higher plant species within arable and horticultural crops. It is not concerned with off- target effects, such as drift to seminatural habitats, but is particularly concerned with the biodiversity implications of herbicide use within crops.

The overall objectives of this desk study was to review the known effects of herbicides on weed populations and communities within arable crops and to review the subsequent indirect effects on fauna, to identify gaps in knowledge, to prioritise research needs and to examine potential approaches to a) risk assessment for non-target plants in fields and b) practical means of maintaining appropriate weed cover in crops.

Contents

Chapter 2 Ecology of representative weed species

Chapter 3 Updating pn0923 - non-target effects of herbicides

Chapter 4 Changes in above-ground weed abundance

Chapter 5 Non-target weed species in the seedbank

Chapter 6 Current weed control and its impact

Chapter 7 Effects of management other than herbicides on farmland biodiversity

Chapter 8 The impact of herbicides on invertebrates

Chapter 9 Relationships between weeds, herbicides and birds

Chapter 10 Risk assessment for non-target plants within crops

Chapter 11 Practical weed control, biodiversity and risk avoidance

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Connected Content

 Weeds represent a significant and ongoing constraint to horticultural production.  This report 1. reviews the known effects of herbicides on weed populations within horticultural crops and the consequent indirect effects on fauna; 2. summarises the impact of weeds on horticultural crops; 3. Assesses perceived beneficial effects of weeds on the biodiversity of horticulturally based agro-ecosystems