Weed Management Handbook

430 Pages·2002·14.82 MB·English

by  Robert E. L. Naylor

Weed Management Handbook
Ninth Edition
Edited by
Robert E.L. Naylor
Trelareg Consultants
Finzean, Banchory, Scotland
Published for the British Crop Protection Council
by Blackwell Science
Bl ac kwelI
Science
0 2002 by British Crop Protection Enterprises Ninth edition published 2002 by Blackwell
Science Ltd
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Contents
Introduction V
1 What is a Weed? 1
Robert E.L. Naylor and Peter J. Lutman
2 Weed Competition 16
R.J. Froud- Williams
3 What is the Weed Seed Bank? 39
Andrea C. Grundy and Naomi E. Jones
4 Weed Population Dynamics 63
Robert E.L. Naylor
5 Weeds and Biodiversity 75
E.J.P. Marshall
6 Herbicide Discovery 93
Leonard G. Copping
7 Herbicide Legislation and Regulation 114
D.J. Flynn
8 Herbicides: Modes of Action and Metabolism 134
John P.H. Reade and A.H. Cobb
9 Herbicide Formulation and Delivery 171
Duncan Webb
10 Methodology of Application 199
T.H. Robinson
11 Herbicide-Resistant Weeds 225
Stephen R. Moss
12 Herbicide-Tolerant Crops 253
Ralph C. Kirkwood
13 Non-chemical Weed Management 280
W.B ond
iii
iv Cont ents
14 Integrated Weed Management 302
Robert E.L. Naylor and Caroline Drummond
15 Developing Decision-Support Systems to Improve Weed Management 3 11
James Clarke
16 Optimising Herbicide Performance 323
Per Kudsk
17 Biological Control of Weeds 345
M.P. Greaves
18 Weed Management Strategies for Winter Cereals 354
James Clarke
19 Weed Control in other Arable and Field Vegetable Crops 359
C.M. Knotf
20 Management of Aquatic Weeds 399
Jonathan R. Newman
21 Where is Weed Management Going? 41 5
Robert E.L. Naylor
Index 419
Introduction
The first edition of the Weed Control Handbook appeared in 1958 and the eighth
edition in 1990. Weed control has changed since the last edition. New ideas,
information and understanding have been incorporated into weed management
systems. More importantly, new weed management challenges are presenting
themselves and need to be addressed.
In previous editions the subject has been divided into two areas and the
Handbook was issued in two volumes: Principles and Practice. For this edition it
has been decided to merge the two areas into one volume. This more effectively
demonstrates the linkage of knowledge and information with weed management
practice. As we have learnt more, so we have evolved our weed management
systems to be both more effective and at the same time less harmful to the
environment.
The change in title from Weed Control Handbook to Weed Management
Handbook is a deliberate one. The emphasis in cropping systems is now much
less on production. Agricultural policy at EU, UK and regional scales now pays
far more attention to producing food in a sustainable and ethical manner.
Agenda 2000, the main agricultural policy instrument of the EU, makes the
environment more central to agricultural policy. The policy states '. . . The inte-
gration of environmental goals into the CAP and the development of the role
farmers can and should play in terms of management of natural resources and
landscape conservation are increasingly important objectives for the CAP . . .'.
Clearly, the objectives of arable cropping are influenced by this and indeed the
role of farmers is changing to one of countryside managers. The former UK
Ministry of Agriculture, Fisheries and Food (MAFF; now the Department for
Environment, Food and Rural Affairs, DEFRA) has evaluated the effects of the
revised agreement on Agenda 2000 made at the Berlin Heads of Government
meeting in March 1999. MAFF estimated that the UK arable sector would lose
El80 million. Relative to other countries in the EU, the package was estimated
to make wheat more profitable in the UK, but protein crops and oil crops less
profitable.
Clearly, this influences which crops are grown and also signals that the cen-
tral feature of cropping systems will be to drive down costs of production.
Growers can achieve this through the use of both biotechnology and non-bio-
technology. On the non-biotechnology front, the focus is to achieve greater
efficiency of utilisation of resources. Knowledge and information technology
have a role in providing better decision making while engineering solutions
can achieve greater efficiency through, for example, more accurate and loca-
lised placement of fertilisers and agrochemicals. On the biotechnology front,
the attractiveness of many of the new cultivars (conventional or genetically
V
vi Introduction
modified) that are becoming available is that they lead to easier and cheaper
crop protection.
At the same time, the regulation of activity on farms is increasing. The
requirement of society is that growers achieve production in an environmentally
benign way. Thus, crop production is a challenging activity. Increasingly, the
decisions made in managing crops have an important financial consequence but
the options are constrained. This is particularly so in the field of crop protection,
where a high proportion of compounds will cease to be registered and will
therefore not be available for use.
This book comprises a series of chapters written by experts in their field, in a
sequence that reflects a progression from the biology of weeds, through the
underpinning science and technology relating to herbicides, to principles of weed
management techniques and finally a set of ‘case studies’, describing the main
options available. There is more emphasis than in previous Handbooks on
techniques to reduce the application of herbicides through the incorporation of
mechanical and biological methods of weed management into what can be
termed ‘integrated weed management’.
Weed scientists and technologists interact greatly with each other and all
have a clear focus on the question of how we limit weed populations in
crop fields (and elsewhere). The authors in this book have illustrated the
links between the various disciplines and subject areas that contribute to
‘weed management’. Inevitably, this means that there is a degree of overlap
and cross-reference between the chapters. As editor, I have not tried to limit
this overlap because the links are important; weed management decisions
must be based on as complete a knowledge and information set as possible
if the decisions are to be sound and effective. Occasionally readers will
notice differences of interpretation between authors. Again, I have not tried
to impose a uniform view, as the open discussion of such issues is healthy
for the subject because it exposes our ignorance and identifies where we
need further research or development.
Weed management does not stand still and it is not the same as it was ten years
ago. Nor will it be the same in ten years’ time when new weed problems will have
arisen in response to changes in cropping systems. Different management systems
will be developed to deal with these. The new management systems will have to
conform to the demand of society for solutions which are at least environmen-
tally benign or, better, lead to enhancement of the countryside for all to enjoy. At
the same time the new solutions have to be cost-effective in a tighter financial
climate.
I thank all the contributors for the time and effort they have devoted to writing
their chapters. Without them, there would be no Handbook! I also thank BCPC
for their foresight in producing a new edition and their trust in asking me to edit
it. The weed science community is small but active and I am sure an updated
version will be needed in another ten years to take account of the new knowledge
about weeds and the fresh technology that can be brought to bear on managing
Introduction vii
weeds. The poet Gerald Manley Hopkins said ‘Long live the weeds.. .’ (Invers-
naid). We need to add ‘long live the weed scientists’!
Bob Naylor
Editor
Aberdeenshire
Weed Management Handbook, Ninth Edition
Edited by Robert E.L. Naylor
Copyright © 2002 by British Crop Protection Enterprises
Chapter 1
What is a Weed?
Robert E.L. Naylor
Trelareg Consultants, Finzean, Banchory, Scotland AB31 6NE
Peter J. Lutman
IACR Rothamsted, Harpenden, Herts AL5 2JQ
Synopsis
What is a weed? Why is it a weed? What features of its biology make it a weed?
This chapter is concerned with answering these questions, and with the way in
which knowledge of weed biology helps to devise weed management strategies.
Definitions
There have been numerous definitions of weeds. Older ones include ‘a plant not
valued for its use or beauty’ and ‘a plant whose virtues have yet to be discovered’.
However, most modern definitions convey an opinion that the plants are con-
sidered undesirable in some way. This is reflected in the German term unkraut
and the French malherbe. A great variety of reasons can account for a plant being
unwanted but most encompass a view that the plant is a nuisance and in some
way hinders or interferes with human activity. This leads to the understanding
that crops may at some time also be weeds. For example, the grass plants growing
in the domestic garden lawn are acceptable and encouraged, but when they
spread to the adjacent flowerbed they are considered weeds. Similarly, crop seeds
which are shed in the field can grow in subsequent crops in following years and
contaminate them. The definition of weeds adopted by the European Weed
Science Society is ‘any plant or vegetation, excluding fungi, interfering with the
objectives or requirements of people’. Similarly the Weed Science Society of
America has adopted the definition ‘a plant growing where it is not desired’.
Reasons for classifying a plant as a weed
The definitions above emphasise that there is nothing special about the biology of
weed plants but they merely have to interfere with the activity of humans. We
generally think of weeds as being a nuisance because they interfere with
agricultural activities, but Table 1.1 summarises some of the other reasons for
1
2 Reasonsfor classifying a plant as a weed
Table 1.1 Reasons for calling a plant a weed
Justification Mechanism Examples
Reduce crop yield Interference with access to Avenaf atua, Galium aparine
plant growth resources of in cereals, Poa annua in
light, water and nutrients grassland
Reduce crop quality Admixture of contaminating Sinapis arvensis in oilseed
seeds in arable crops rape
Contamination of vegetable Solanum nigrum berries in
crops peas
Delay harvesting Conservation of moisture Matricaria spp. in oilseed
may delay ripening and rape
increase crop moisture level
when harvested
Interfere with Climbing plants make Fallopia convolvulus
harvesting combine operation more
difficult
Vigorous late-growing weeds Chenopodium album
can interfere with
harvesting potatoes and
sugar beet
Interfere with animal Plants with spines or thorns Cirsium arvense
feeding inhibit animal foraging
Cause poisoning Senecio jacobaea,
Digitalis purpurea,
Laburnum anagyroides,
Rhododendron ponticum
Taint animal products Impart undesirable flavour, Allium ursinum,
e.g. to milk Ranunculus spp.
Act as plant parasites Cuscuta spp.
Reduce crop health Act as alternate or alternative Cruciferous plants harbour
hosts for crop pests and clubroot; many grasses
diseases harbour ergot of cereals
Increased vegetation at base Weeds in oilseed rape can
of crop increases moisture increase levels of Botrytis
level and levels of disease
Reduce animal (and Act as intermediate hosts or a Grass
human) health vehicle for ingestion of
pests and parasites
Photosensitisation Hypericum perforatum
Teratogens Pteridium aquilinum
Are a safety hazard Reduced vision on roadsides Tall plants
Fire risk under electricity Any plants, but especially
lines scrub
Contd.
What is a Weed? 3
Table 1.1 Contd.
Justification Mechanism Examples
Reduce wool quality Hooked seeds reduce value of Bidens spp.
fleeces
Prevent water flow Plant mass blocks ditches and Elodea canadensis
irrigation channels
Exhibit allelopathy Release of substances toxic to Little evidence this occurs in
crop plants the field in northern
European agriculture but it
may be relevant in tropical
conditions
Impact on crop Vegetation prevents
establishment establishment of young
trees
considering plants to be weeds and therefore for managing their occurrence. The
examples given are from northern Europe, and are considered in more detail
below.
Reduction of crop yield is the major reason for attempts to reduce weed
populations in arable crops, but effects on crop quality are almost as important
for horticultural crops. The first attempts at controlling weeds used manual
labour and hand-pulling or hand-hoeing. A major advance was the mechanisa-
tion of the process, permitting a greater area to be covered in a day. The tech-
nology required the development of a machine to sow the crop in rows so that the
weeds in the spaces between the rows could be easily removed by an implement
drawn behind a power source (animal or mechanical). This was the main method
of weed management from the early 19th century up to the middle of the 20th
century in developed countries and is still practised successfully today, around the
world.
A major revolution was the development of herbicides in Britain, the USA and
Switzerland. The ability to reduce weed populations growing in crops has been an
important component of the increased food production by western agriculture.
The recorded increases in crop yields in the UK over the 50 years since 1940, of 1
tonne every ten years (Fig. 1. l), contain contributions from a number of sources,
including improved varieties of higher potential yield, improved crop nutrition
and improvements in all aspects of crop health, including weeds. In trials,
unweeded control plots provide a comparison with plots on which the weed
population has been severely reduced (Fig. 1.2). Clearly the impact of weeds on
crop yield can be considerable, or more accurately, some weed species have a
large impact on crop production. This leads to consideration of the relative
impact of different weed species which then allows the prioritisation of weed
management options. The most important weed species which have the largest