Integrated control of slug damage in organic vegetable crops- OF 0158

Summary

Slugs are important pests of a wide range of organic vegetable crops, which are high quality products, desired by consumers. Slug problems are especially acute in comparison to conventional vegetable production because use of chemical control measures is prohibited. The purpose of this project is to provide organic vegetable growers with effective integrated pest management techniques for control of slug damage. The project builds on the results of MAFF Project No. OF0137 (September 1996 to March 1999), which demonstrated that biological control using slug-parasitic nematodes (Phasmarhabditis hermaphrodita) can give effective and long-lasting control of slug damage to organic vegetable grown in polytunnels in autumn and early spring.
Project OF0158 has established a number of techniques that are suitable for use by organic growers for integrated control of slug damage. Importantly, ineffective techniques were also identified. The results clearly indicate that no one method of control will give a sufficient reduction in slug damage where problems are severe. Suitable combinations of control measures are necessary. Key points are summarised below:
• Cover crops: where these are grown for short periods only to prevent nutrient leaching, ryegrass should result in less severe slug problems in a following crop, compared to legumes such as red clover or vetch.
• Where a fertility–building leguminous crop is required, lucerne appears to result in slower growth in the slug population than other popular legumes (clovers and vetch) .
• A period without a fertility crop over winter, following an annual vetch crop, reduced slug populations to levels similar to those on plots without cover crop, by the following spring.
• Slug-parasitic nematodes (Phasmarhabditis hermaphrodita), electrical barriers and hand-picking of slugs can all be effective methods of control. They provide additive effects for slug control and, as an integrated package, they can make the difference between a valuable crop and almost complete failure due to slug damage.
• Single applications of nematodes were ineffective in some experiments. Work in a related EU project indicates that the commercial strain of the nematode is now less effective than new strains isolated at Long Ashton Research Station.
• The carabid beetle, Pterostichus melanarius, was not able to prevent contamination of cabbages by slugs at harvest in September, even though crops were grown in the field throughout the beetles’ main period of activity.
• Mechanical control of weeds (hand hoeing) did not reduce slug damage, even when done as frequently as twice per week.
• Importantly, work in OF0158 has identified the possibility of devising systems of integrated control of slugs and weeds, both of which are the major crop protection problems facing growers of organic vegetables and soft fruit. Further work is warranted in order to develop practical systems for protecting crops from slugs whilst benefiting from their feeding activities in killing weeds.