Report from the Sub-comittee on the environment and health

Prevention of weed
problems and use of
mechanical control
methods
Cover of vegetation all
year round
9 Environmental and health
assessment of alternative or new
methods of weed control and
control of pests
9.1 Introduction
In <strong>the</strong> following, an assessment is made of <strong>the</strong> environmental and health
consequences of non-chemical methods of preventing and controlling
pests in agriculture. The assessment is based on <strong>the</strong> work of <strong>the</strong> <strong>Sub</strong>committee
on Agriculture. It is followed by a discussion of:
• possible improvements at sites for washing and filling sprayers
• <strong>the</strong> interaction between pesticides and <strong>the</strong> production of toxins
• mineralisation in <strong>the</strong> soil with increased soil treatment in connection
with no use of pesticides
• changes in energy consumption and emission of greenhouse gases in
connection with no use of pesticides
• new pesticides.
9.2 Weed control
To achieve adequate control of weeds in <strong>the</strong> event of a total or partial
phase-out of pesticides, it would be necessary to combine prevention and
control through cultural practices and non-chemical, alternative methods.
That means that <strong>the</strong> crop rotation would have to be adjusted towards less
winter cereal, leading to a more diversified crop rotation and greater
biodiversity than in a crop rotation including monoculture of cereals. In
addition, <strong>the</strong> autumn sowing would have to be done later and it might be
necessary to sow some crops with a wider row spacing to enable
mechanical weeding. If <strong>the</strong> mechanical weeding were very effective, <strong>the</strong>
amount of weeds would not differ much <strong>from</strong> <strong>the</strong> amount in fields treated
with pesticides, so <strong>the</strong>re would be no environmental benefit for <strong>the</strong> wild
flora. In crops such as rape, mechanical methods are already competitive,
compared with chemical methods. Mechanical weed control has a
considerable negative impact on <strong>the</strong> soil’s mesofauna and macrofauna,
particularly springtails and earthworms, and harrowing can damage <strong>the</strong>
crop. On <strong>the</strong> o<strong>the</strong>r hand, increased mechanical control of weeds in
farming would be generally environmentally beneficial because it does
not involve any risk of pollution of groundwater or of spreading of
pesticides to adjacent areas. Placing fertiliser at <strong>the</strong> individual plant is
deemed to be ano<strong>the</strong>r good way of improving <strong>the</strong> crop’s ability to
compete with weeds. All else being equal, this could reduce fertiliser
consumption and thus reduce <strong>the</strong> loss to <strong>the</strong> surroundings.
According to Action Plan II, “Organic Farming in Development”, it is
possible to keep <strong>the</strong> soil covered with vegetation all year round (Danish
Directorate for Development 1999). In organic farming, extensive use is
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