Report from the Sub-comittee on the environment and health

Effect on seed production
The wild flora in hedgerows
and small biotopes
Effect on <strong>the</strong> flora through
spray drift
slowly, it would be necessary to establish permanent spray-free and
fertiliser-free edge zones.
It has been shown that sub-lethal doses of herbicides lead to a reduction
in plants’ seed production. The reduction is related to <strong>the</strong> dose, and this
is probably directly related to a smaller biomass production (Rasmussen
1993; Andersson 1994). For example, a sub-lethal dose (1/2 <strong>the</strong> normal
dose) of isoproturon resulted in a 50 per cent reduction in seed
production in common pennycress (Hald 1993). In a Danish study it was
shown that seed production in unsprayed field plots was 6-14 times
higher than <strong>the</strong> seed production in sprayed plots (Kjellsson, Rasmussen
1995). At <strong>the</strong> same time, spraying with herbicides (dichlorprop + 2,4-
D/MCPA in normal dosage) resulted in a smaller proportion of <strong>the</strong>
surviving plants being able to propagate. It has been shown that some
herbicides (tribenuron-methyl and, to a lesser extent, MCPA) can result
in a smaller seed size in some species, such as black bindweed,
goosegrass and common pennycress (Andersson 1994). With this
knowledge and different scenarios for herbicide use (0 and 100%), it
would be possible to model and estimate <strong>the</strong> effects on <strong>the</strong> seed pool in
farmland and <strong>the</strong> consequences in <strong>the</strong> form of changes in <strong>the</strong> frequency
and composition of <strong>the</strong> vegetation (Kjellsson, Rasmussen 1995; Madsen
et al. 1996, 1997, 1999).
Herbicides are normally not used in hedgerows and small biotopes, so
any impact on <strong>the</strong>se areas is due to unintended effects <strong>from</strong> agricultural
use of herbicides, e.g. through spray drift (see section 4.1.6.2). During a
5-year period, <strong>the</strong> flora in Danish field hedges showed a slight tendency
to contain more species along unsprayed edges of fields than along
sprayed ones (Hald et al. 1994). A 50% standard trial treatment with <strong>the</strong>
herbicide fluroxypyr of a fallow field on sandy soil in <strong>the</strong> Ne<strong>the</strong>rlands
reduced <strong>the</strong> content of species (Kleijn, Snoeijing 1997). Effects on
survival at lower dosages (5 and 10 %) were only found for a few species
in some years. In ano<strong>the</strong>r Dutch study, de Snoo (1997) found, in a threeyear
trial, increased species diversity in unsprayed field edges in sugar
beet, potatoes and winter wheat, primarily as a consequence of an
increase in <strong>the</strong> number of dicotyledonous plants.
There exists a set of standardised values <strong>from</strong> Germany for spray drift.
The values are based on 16 field trials in <strong>the</strong> period <strong>from</strong> 1989 to 1992,
where, on <strong>the</strong> basis of a 95% percentile, a so-called “realistic worst case”
was established (Ganzelmeier et al. 1995). On <strong>the</strong> basis of <strong>the</strong>se values
and known effect thresholds (PC Plant Protection), a qualitative analysis
can be carried out of <strong>the</strong> effects on plant growth. The method used by
Ganzelmeier is not necessarily ecologically relevant. The deposition was
measured during spraying with a single spray plume, and <strong>the</strong> spray
product was collected on flat targets laid on <strong>the</strong> ground. Such data are
relevant for estimating <strong>the</strong> effect on plants that have not yet germinated
and for “flat” areas like ponds and lakes. However, plants that have
germinated and are established “catch” more of <strong>the</strong> spray product. Both
Davis et al. (1993) and Bui et al. (1998) found that different “targets” had
different “catch efficiencies”. “Targets” that rise above <strong>the</strong> ground and
have a complex structure catch more spray product than objects lying flat
on <strong>the</strong> ground. Finally, Nordby and Skuterud (1975) found that <strong>the</strong> dose
of spray product needed to trigger a given effect is smaller for plants in
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