Slugs are an increasing concern for arable farmers, especially in light of the impending ban on metaldehyde pellets. Wendy Short talks to Dr Jenna Ross, who has just completed a report for her Nuffield scholarship on ways of dealing with slugs and how the UK should be improving its biosecurity protocols.

SLUGS have always been one of the arable farmer’s main enemies and the impending spring 2022 ban on metaldehyde pellets is causing concern.

Scientist, Dr Jenna Ross, has studied the pests closely and produced a detailed report for her Nuffield scholarship. She suggests that a UK-wide survey is needed and that border biosecurity protocols should be ramped up, because more than 50 per cent of species are believed to be exotic.

The slug population is constantly evolving and the pest is a prolific breeder, with up to 500 eggs per slug being laid. One of the most common among the exotic species is thought to be the Spanish slug, said Dr Ross.

Dr Ross says: “Little is known about the impact of the Spanish slug and the extent of its distribution, not to mention other species invasions.

“It is imperative that we try and stop slugs from being brought into the country. In the USA, scientists have given border control staff training in slug species identification. Import checks are conducted, including from one state to another.”

Ferric phosphate is a relatively new weapon in the battle against slugs, she pointed out.

She says: “Some manufacturers claim that a wet-processed, durum wheat-based product is superior to a dry version. However, it is widely accepted by all that pellet applicators must be specifically calibrated for individual products.

“There is little evidence of studies being carried out on the potential for ferric phosphate product resistance and if farmers switch from metaldehyde, we have no knowledge of any potential environmental impact.”

Currently, slug monitoring relies on farmers manually trapping and counting slugs, in order to review thresholds. In the future, growers will need to look more closely at integrated pest management strategies, including monitoring, advised Dr Ross. She has been involved in the development of SlugBot, an autonomous slug monitoring and treatment system. Supported by Innovate UK, it brings expertise from robotics, machine learning, phenotyping, malacology and biocontrol.

During her Nuffield studies, Dr Ross looked at conclusions drawn by Dr Hayley Jones of the Royal Horticultural Society.

Dr Ross says: “Her work covered serrated copper tape, grit, pine bark mulch and eggshells, as well as wool pellets, but none of these methods appeared to offer superior control. "Nevertheless, Dr Jones was keen to further investigate copper tape, as it was unknown whether the varnish coating on the commercial product was hindering its efficacy. In California, copper barriers are widely used in plant nurseries.”

Dr Ross pulled together a number of other research findings from around the globe as part of her work.

She says: “Ploughing will control slugs through mechanical damage and by bringing slugs and eggs to the surface for exposure to UV radiation, desiccation and predators. The move towards min-till and no-till may increase numbers, so many advise cultivating the top 25-50mm of the soil. Whatever the cultivation method, clods and cavities should be minimised and any straw should be mixed in.

“A firm seedbed is preferable, and ideally crops should be sown as early as possible to ensure they pass the critical stages safely. When drilling winter cereals into a cloddy seedbed, slug damage could be reduced by drilling at a depth range of 4-5cm.

“Another investigation found that linseed may be less vulnerable and it also dries out the soil. In New Zealand, it was thought that grazing played a key role in crushing slugs. Meanwhile, trials by Natural England indicated that cover crops did not lead to higher slug numbers.”

Another area of worldwide research has focused on the concept that slugs and their by-products have useful properties, she added.

“Unlike snails, slugs have no exterior shell protection so they have evolved to possess exceptional healing abilities. Their mucus has been found to contain anti-viral agents, for example, while the material is already being utilised as an ingredient in beauty products such as face masks. There is thriving market for snails for the food industry and slugs could possibly be viewed as a viable alternative.

“The study of slugs in general appears to be in difficulty; no clear plan is in place and research funding is limited,” concluded Dr Ross. “We need to promote the subject to the next generation and encourage opportunities for knowledge sharing.

“It is possible that we are missing an opportunity. We should perhaps be investigating ways of farming slugs and targeting the animals and their by-products towards the food, pharmaceutical and cosmetic industries.”

Dr Ross is an honorary research fellow at the University of Aberdeen and international business development manager for Crop Health and Protection.

Dr Ross makes the following recommendations for biosecurity protocol in the UK.

  • Identify slug specialists around the country;
  • Develop a central inspection system and a legal framework, to allow commodities to be held for analysis, action and control;
  • Set up a digital imaging system for relevant imported commodities;
  • Encourage collaboration between government departments and government-to-government.