Partner und Internationale Organisationen
(Englisch)
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Long Ashton Research Station, Bristol (UK) MicroBio, Cambridge (UK); Experimental Station, Harpenden (UK); Research Station for Applied Research for Arable Farming and Field Production of Vegetables, Lelystad (NL); University of Santiago, Santiago de Compostela (E); Forschungsinstitut für biologischen Landbau, Frick (CH9; FarmForest Research, Montpellier (F)
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Abstract
(Englisch)
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Slugs cause damage to a large number of crops, including many vegetables. At present, slugs are mostly controlled with bait pellets which contain either metaldehyde or a carbamate. These products cannot be used in organic agriculture, are relatively toxic or have negative effects on the environment. This project therefore aims at finding alternative methods of slug control. We investigate the optimal conditions for application of a recently discovered nematode biocontrol agent, search for better nematode strains and study cultural methods for reduction of slug populations or slug damage.
In Switzerland, the grey field slug (Deroceras reticulatum), garden slugs (Arion hortensis agg.) and the Spanish slug (Arion lusitanicus) are particularly pestiferous. In this project, we discovered that not only A. distinctus, but also A. hortensis are frequent in Switzerland. The two species look very similar. Also, we found that they have similar feeding capacities and react similarly to a range of molluscicides. Thus, it is not necessary for practitioners to attempt to distinguish the two species.
The commercialized strain of the nematode Phasmarhabditis hermaphrodita (product BioSlug / NemaSlug), is known to act differently on slugs of different species and body size. We therefore determined its size-specific effectivity against the three most important pest slug species of Switzerland. The field slug Deroceras reticulatum was susceptible to the nematodes at all ages. The Spanish slug Arion lusitanicus was highly susceptible shortly after hatching, but its susceptibility decreased gradually with increasing body weight. Garden slugs, Arion distinctus and A. hortensis, were not very susceptible to nematode infection. Several application strategies for the nematodes were tested in the field (standard and early application, splitting of dosages). In all cases, effectivity of the treatment (measured as inhibition of slug damage) was insufficient, probably because of the prevalence of the slug species A. lusitanicus, which is not very susceptible to the nematodes.
In order to find more effective strains of slug parasitic nematodes, almost 1600 slugs were collected in different regions of Switzerland and screened for natural nematode infections in 1998 and 1999. 67 nematode strains were found and sent to Long Ashton for identification and further testing. Some strains belong to the species P. hermaphrodita, and some strains belong to another species, provisorically called 'nematode A'. Nematode A is also slug-parasitic and seems to withstand higher temperatures than P. hermaphrodita.
A slug repellent mulch material and a repellent organic fertilizer were tested in the laboratory and in mini-plot field trials. Both materials showed some effectivity in the laboratory, but their effect was not sufficiently persistent to result in significant protection of crops in the field. A pinecone extract said to be repellent for slugs did not reduce slug damage in the field.
A new slug pellet containing iron(III)phosphate gave promising results in mini-plot trials in 1999 and 2000, as well as in some on-farm trials carried out in 2000.
In an attempt to control immigration of Spanish slugs into horticultural crops, several types of slug fences were investigated. Under severe slug pressure, none gave sufficient protection. Bran barriers gave promising results in preliminary trials in 1999, but proved insuccessful in a mini-plot trial and several on-farm trials carried out in 2000.
In the vicinity of wildflower strips, Spanish slugs were more frequent and slug damage was greater than further inside the field. By contrast, numbers of field slugs and of garden slugs were not elevated near wildflower strips.
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