Slugs, Snails and Iron Based Baits: An Increasing Problem and a Low Toxic Specific Action Solution

Abstract

Slugs and snails are growing as a significant problem around the world. The problems extend to damage to vegetation and crops, contamination, quarantine problems, disease carriers such as flukes, and poisonings of both micro and macro non-target species by baits. This paper traces the history of slug and snail controls worldwide, addressing the latest developments in low-toxic, specific, and highly effective molluscicides. The action of the various molluscicides and the importance of natural predators and farming practices are also explored. The paper briefly discusses why the problem is becoming more significant globally with current practices of minimum tillage and high organic matter buildup in the soil. Furthermore, best practice monitoring techniques and bait application are mentioned, with particular emphasis on the Australian-developed bait based on an iron chelate FeEDTA complex in the mid-1990s.

Keywords:

• Slug
• Snail bait
• Molluscicide
• Iron chelate

Introduction

During the last forty years, the major chemical controls used against slugs and snails have been baits based on either metaldehyde or methiocarb as the active ingredients. Metaldehyde, initially used as a firelighter, became known as a slug killer in the 1930s. Methiocarb-based baits were developed in the 1960s. Simple metal salts have been known to be toxic but generally repulsive to mollusks since the 1890s. Recently, the development of a mollusc-specific iron chelate-based bait has proven to give significant control without any appreciable toxicity concerns.

Recent Significant Developments in Bait

Major efforts have been applied to find new methods of controlling slugs in agriculture. Various novel methods and approaches have been explored with some success, including work on nematodes, predators such as beetles, and repellents. Nevertheless, the most popular and effective method of slug control in today's agriculture is still baiting. Over the last 25 years, the use of baits has grown rapidly around the world. Concerns about the toxicity of current baits on beneficial non-target species, mammals, and the environment continue to grow. Despite the quest by companies and researchers for a more acceptable and viable method of tackling the problem, there have been few significant developments. Some work with a group of chelates being evaluated as contact poisons and stomach poisons was undertaken in the late 1980s to early 1990s. It wasn't until major formulation developments of various metal chelates incorporated into a bait that a new generation of molluscicides became a commercialized product and was registered in Australia with an active ingredient Iron EDTA complex under the brand name Multiguard®.

Increase in Slugs as a Major Agricultural Pest

During the last 25 years, there has been significant growth in slugs as a pest. Some of this is likely to be attributed to the wider distribution of the pest through more extensive transportation of produce, etc. The grey field slug (Deroceras reticulatum) is the most widely distributed pest slug species and has readily adapted to environments in many countries. The importance of slugs as pests increased almost simultaneously with the growth in minimal/zero tillage, direct drilling of cereal and other crops. The significant benefits to agricultural systems of minimal tillage and retaining high levels of organic material in the soil have also brought with them challenges in controlling a number of pests. Some of these problems appear to stabilize, but slugs are listed as one of the major pests that benefit from this farming practice.

Slugs in Australia

The problem of slug damage in Australia appears to be growing. It is stated that farmers underestimate losses caused by slugs, as they do most of their damage at night, or even below the surface, often going unidentified or passed off as poor germination or damage caused by cutworms. In Australia, slugs are a problem in the higher rainfall climates stretching from southern Western Australia, South Australia, NSW, Victoria, and Tasmania. Certain crops, such as lettuce, strawberries, and certain vegetables and herbs, are dramatically affected by slug damage. Other crops, such as poppies, wheat, barley, onions, lentils, pyrethrum, pasture, and canola, may be damaged by slugs as seeds or seedlings just after they begin to shoot, requiring protection until they are established.

Monitoring and Application Control Techniques

The initial step in determining the need to apply a bait involves looking for and identifying the likelihood and size of a slug problem before they have a chance to attack, damage, or destroy the plant seeds or shoots. Traps, such as a piece of hardwood or masonite placed on the ground, can be used to assess the slug problem.

Iron Chelate Baits as a Chemical Control

Iron chelate baits are relatively new in commercial applications but are well-established in the home garden market. In comparison with methiocarb and metaldehyde, iron chelate baits are mollusc-specific and have shown superior effectiveness and lower toxicity to non-target species.

Mode of Action

The iron EDTA complex has been found to be the most effective for molluscicide, where the iron is released in the mollusc's gut and is toxic if the concentration is sufficiently high. Unlike other chemical baits that work through paralysis, iron-based baits allow snails to move away from the bait and return to their shelter before dying.

Future Directions in Slug Control

It is predicted that low-toxic, specific iron-based baits will become established for controlling snails and slugs. A better understanding of the ecology of these pests will help to maximize the effect of farming procedures, natural biological control, and chemical control, minimizing crop damage. Future research and development may lead to long-lasting iron-based baits that are effective for extended periods.

References

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