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Life history variation in weed populations: implications for weed management and adaptation in agri-ecosystems - IF01103

Globally and in the UK, weeds cause greater yield losses than any other crop pest and vast sums are spent on weed control annually, often with a significant cost to the environment. In the last 30-40 years, agricultural weed control has been dominated by herbicides. More recently, however, environmental concerns, regulatory pressures and evolved weed resistance are limiting herbicide options for weed control, leading to calls for a more integrated and environmentally-benign weed management. An improved understanding of weed biology, ecology and adaptation in agroecosystems is a basic requirement for integrated weed management.

In a herbicide-limited future, weed management will need to integrate judicious use of remaining herbicide options with advances in physical weed control and a greater emphasis on cultural weed management. Chemical and physical weed control methods are predominantly technology-led and focus on removing weeds from the crop sometimes resulting in negative environmental, ecosystem and human health impacts. Cultural weed management, on the other hand, is biologically-driven and attempts to limit weed impacts by reducing weed establishment in crops, maximising crop competition and reducing weed fecundity by, for example, promoting precocious weed germination, varying crop sowing times, increasing crop competitiveness and minimsing seed return to the seed bank. Cultural management is driven by ecological principles and can only be reliably achieved if we can understand, predict and manipulate the timing of key life history events.

Weed evolution over the course of hundreds of years of crop cultivation has ensured that the timing of these key weed life history stages and transitions coincides with or avoids pivotal crop management practices (crop establishment, weed control, crop harvest) to maximise population growth rates and weed persistence. The key life history stages and processes that dictate the fitness of crop weeds are dormancy and germination, vegetative growth rates, the timing and duration of flowering and reproductive allocation. This project will begin to unravel the inter-relationshships between these processes and importantly, the degree of intra- and inter-population variability in the timing of life history stages and transitions. By conducting some experiments in thermogradient tunnels, the project will also provide insight into interactions between temperature and weed life histories and, in doing so, provide some indication of the likely impact of climate change on the ecology and management of major UK weed species.

Experiments will be conducted with multiple populations of two key UK weed species to assess the extent of life history variation in important weed traits. Populations of these two species will be collected from across their range in the UK and will be sown in modular trays which will be placed in the field at HRI and in thermogradient tunnels. Emergence patterns for these populations will be observed and individual plants, representing the range of emergence times, will be transplanted into a crop (field) or into pots (thermogradient tunnels). Destructive and non-destructive measurements of growth rates, flowering time and duration and seed production will be made on individual plants and correlations between different life history traits will be explored with appropriate statistical analyses. Experiments will also explore the impacts of genotypic and maternal environment effects on life history characteristics. These experiments will address the following questions:

• How much life history variation is there within and between UK weed populations?
• Is life history variation likely to prevent the development of generic integrated weed management recommendations?
• What are the relationships between life history stages and processes i.e. germination and flowering time?
• Does life history variation suggest that weed species will rapidly adapt to changing weed management and a changing climate?
• How could weed population dynamics models be modified to account for within- and between- population variability?

The weed biology data and understanding generated by this project will be used in follow-on projects which combine modelling and agronomic field trials to develop and evaluate novel, culturally based weed management systems. Ultimately, the current project will help to support the development of practices that will:

(i) increase the potential for cultural and integrated weed management to reduce weed impacts in crops by reducing weed establishment, competitiveness and seed production,
(ii) reduce selection for weedy traits that circumvent or compromise weed management and,
(iii) help to predict future weed problems in the face of changing cropping and weed management practices and a changing climate.
7. (b) Objectives

Motivation for the present study
In the last 30-40 years, agricultural weed control in the UK has become dominated by herbicides. Now however, regulatory changes at EU and national levels, driven by environmental and health concerns relating to the use of pesticides, are resulting in the withdrawal of many herbicide registrations. At the same time, there are escalating levels of evolved herbicide resistance in some key weeds. Together, these pressures mean that the long-term sustainability and desirability of herbicide-dominated weed management is questionable. The combined threat of loss of herbicide registrations and increasing resistance were assessed in a recent Defra-funded modelling project (IF0192). This study concluded that the loss of herbicide availability and efficacy could be compensated by a greater focus on integrated weed management. A more integrated systems-based approach to weed management requires a greater degree of understanding of the biology and ecology of individual weed species, as well as an appreciation of the role of weeds as providers of ecosystem services and biodiversity within agroecosystems. A biologically-informed weed management will also need to understand and predict the impacts of climate change on weed-crop interactions, weed adaptation and the invasion of new weed species to the UK.

This project aims to make detailed observations on the biology and ecology of two key UK weed species. Field trials will be designed and data collected and analysed with a view to providing novel insights into how weed biology can be better understood and manipulated to improve the efficacy of cultural weed management in a herbicide-limited future. It is anticipated that this work will lead to future projects in collaboration with levy boards and industry partners (possibly via Technology Strategy Board funding) to develop modelling approaches in combination with agronomic trials to deliver improved cultural weed management.

Objective 1: To quantify within- and between-population variability in key life history traits that determine the fitness of weed populations growing in agricultural crops.

Objective 2: To determine the relationships between weed emergence time and the timing of other key life history events such as flowering, seed production and seed dispersal.

Objective 3: To explore the relative importance of genotypic and maternal environment influences on life history traits and variation.

Objective 4: To quantify variation in life history and fitness of populations of weeds along a temperature gradient to assess likely impacts of climate warming on UK weeds.

Time-Scale and Cost
From: 2010

To: 2013

Cost: £499,203
Contractor / Funded Organisations
Warwick - HRI
Climate Change              
Integrated Farming Systems              
Sustainable Farming and Food Science              
Sustainable Farming Systems              
Weed Control