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Cleaner Technology Projects in Denmark 1997
Insekticidreduktion ved bekæmpelse af nålesnudebillen
Miljørapport nr. 365, 1997, Miljøstyrelsen
The pine weevil, Hylobius abietis,
is one of the most influential damaging insects within forestry.
The gnawing of the insect on the root collar of many pine species results in a weakening
of the plants and, at worse, considerable plant death. In an attempt to reduce the number
of insecticides applied against the pine weevil, a number of experiments on Norwegian
spruce, sitka spruce and larch have been carried out in the period of 1991-1993. This
report describes the results of these experiments.
Two types of experiments were carried out:
- An experiment with four non-chemical methods of prevention was carried through: plant
plates, ‘struten’, plant stocking and BE-MA fibres which all were put on
the plants when planting.
- Furthermore, an experiment was established where the liquid quantity of a standard
remedy permethrine was attempted reduced in relation to a normal dose. For this, a precise
dosing spray equipment was used. Six different liquid quantities were applied as
treatment, but in the same concentration of the insecticide.
The experiments with the non-chemical protection methods showed that they did not
consist of a sufficiently durable material as they weathered during l-2 years. This is not
appropriate, as the pine trees require protection against the
pine weevil for at least three years after planting. Moreover, several of the protection
methods were difficult to mount on the applied plants because the equipment was developed
in Sweden where they are applied as container plants. In Denmark, however, larger
bare-rooted spruces (2/2) are used in forestry and thereby also in these experiments.
Furthermore, several of the protection methods damaged the plants and several of the
methods were not designed to be effective enough to protect the plants from the pine
weevil. Finally, it should be mentioned that the costs, as to application of the
non-chemical protection methods, exceeded, by far, the costs of controlling the pine
weevil by means of chemical pesticides.
The results of the experiments with a reduced quantity of insecticide were, on the
other hand, more suggestive as it appeared from the test results that the usual dose of
approx. 25ml spray liquid per plant may be reduced to 10-15ml, i. e. a reduction of
40-50%, without any changes in the extent of weevil attacks on the Norway spruce. The
situation is however; more problematic for the small larch plants where very little
control was independent of quantity of spray liquid. The effect of the synthetic
pyrethroides may be expected up to two years after spraying.
Besides the experiments, an investigation in the form of a literature study with
reference to study the possibility of developing a warning system for pine weevils was
carried out. The investigation showed that the possibility of setting up a warning system
for pine weevils seemed to be present. But it should be stressed that this, among other
things, requires changes of the growing practice and thorough investigation of the
population dynamic of the pine weevil. Furthermore, it should be emphasised that the
establishment of a warning system will be extremely time-consuming for the forestry.
Author/ institution
Paul Christensen, Anita Fjeldsted Pedersen and Arne Kirkeby-Thomsen
Forskningscentret for Skov og Landskab
This report is subsidised by the National Council for Recycling and Cleaner Production
ISSN no. 0105-3094
ISBN no. 87-7810-819-5
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