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Bekæmpelse af stor nåletræsnudebille uden pesticider

Summary

Alternative defence methods

The pine weevil, Hylobius abietis is the most serious insect pest problem in reforestation of coniferous forest in Denmark. This project has evaluated alternative, non-pesticide countermeasures.

During 2001-2003 experiments were established in 15 areas. In 13 of these, trees were planted in the spring and 2 in the autumn. In all 17,142 trees of five coniferous species (norway spruce, sitka spruce, larch, douglas fir, scotch pine) were used in the project.

Results show that, by using alternative methods, it is possible to reduce damage pressure to an acceptable level. E.g. treatment of the plant’s collar with a wax cover was as efficient as treating with a pyrethroid. Plastic and paper collars working as barriers showed slightly less effect. However, they gave a reasonable reduction in weevil damage.

Tillage was also effective. Total removal of organic material before planting gave the greatest reduction in weevil damage. However, just establishing a nursery bed of mineral soil around each plant also works well, since the weevil avoids the mineral soils.

Shelter tree establishment did not give clear effect in this experiment. From other experiments, however, this method is known to give good protection to the young plants.

The costs of these alternatives seem to be the limiting factor for success of the methods. The methods have been developed for small cover-rooted plants, but they cannot meet their full financial potential with large bare-rooted plants. I.e. it is too expensive in labour to mount the collars on the plants.

For ”Bugstop” (wax) – the most promising defence method – the application method has been industrialised for small cover-rooted container plants.

Until the other methods are further developed, large bare-rooted plants could be preferred, since they better withstand attacks from the Hylobius abietis.

None of the alternative defence methods worked in all cases; neither did the chemical treatment. For the private forestry, insecticides (pyrethroids) still seem the best choice for financial reasons. For pyrethroid treatment plant size is not critical.

The overall conclusion on efficacy of alternative defence methods is that these methods alone or in combination work as efficiently as conventional insecticide treatment with a pyrethroid.

Damage pressure in relation to cutting strength and distance

In several cases damage pressure by the weevils has been observed to be most severe along the borders of the clear-felled area, close to the rows of slash material. However, a spatial analysis using GIS and GPS has proven that although the distribution of feeding pressure by the weevils was shown to have a clumped distribution, the highest densities could not be shown to be related to stumps or slash rows.

A regional analysis of relationship between areas of clear-cuts, distance and damage pressure on newly planted conifers did not prove any significant results. It indicates however an average migration distance of 2-3,000 meters.

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Version 1.0 September 2006, © Miljøstyrelsen.