The Banning Of Metaldehyde Slug Pellets In UK Has Seen A Move To Ferric Phosphate Use, But Is It Safe Around Food, Pets, Children & The Environment?

I’ve written at length about slugs and snail, how slugs can crawl over razor blades and how so few things, such as eggshells, brambles etc deters them. So, with so many things not working what does? And more specifically do the Ferric Phosphate slug pellets we see for sale in garden centres work?

Don’t be fooled into thinking Ferric Phosphate and Iron Phosphate are different. It’s just a different name for the same thing.

Why Is This Important?

Having previously taught FEPA (Food & Environment Protection Act) courses, been a market gardener and now being an “amateur” gardener, safety in the garden and in food production is important to me. After all we eat what we grow. But I see “advice” being given online that is no more than opinion. Often it’s a well meaning person that read an article somewhere and then repeats what they read … or worse still, what they think it meant.

I believe we deserve better than uninformed opinion. I believe we need facts supported by verifiable research, and this is what I have accessed and give below. There are a number of well cited and verifiable research papers listed below.

Yes OR No For Ferric Phosphate Slug Pellets?

If only the question was that easy.

Lumbricus herculeus (left) and Lumbricus terrestris (right); specimens depicted are respectively smaller and larger than average for their respective species.

The thing is perhaps this isn’t quite the right question. The right question is “do they work safely?”

Because there is no doubt that Ferric Phosphate kills slugs and snails. They eat it and, after eating it and crawling away to hide underground, they die. Of course gardener don’t see them die underground so wonder why there aren’t any dead slugs!

The Ferric Phosphate is mixed with bran as this is what the slugs eat. And if that was the only thing to consider I’d recommend it. But to make the mix more effective the manufacturers add EDTA to the mix. EDTA is a problem as I explain below.

Slugs grazing on food crops

EDTA, or Ethylene diamine tetra acetic acid, which is found in most ferric phosphate slug pellets, can be toxic to various animals. Even small amounts can cause severe gastrointestinal issues and red blood cell damage. So it’s important to keep slug pellets away from pets and to use slug control methods that are safer for animals where possible.

The Very Bad Ferric Phosphate News

But there is even worse news. EDTA is also highly toxic to earthworms, and can cause oxidative stress and even death at high concentrations. This means that if slug pellets containing EDTA are used in the garden, it could potentially harm the earthworm population, and worms are important for soil health and the overall ecosystem. So it might be a good idea to avoid using slug pellets containing EDTA and consider alternative, less toxic methods of slug control. Slug pubs work quite as does catching slugs by hand after dark. But the best method is undoubtedly the use of biological control. For example, nematodes.

Research Sources

Ecotoxicological responses of the earthworm Eisenia fetida to EDTA addition under turfgrass growing conditions Duo et al.

Responses of the earthworm Lumbricus terrestris (L.) to iron phosphate and metaldehyde slug pellet formulations. Langan & Shaw, Manchester Metropolitan University

The relative toxicity of metaldehyde and iron phosphate-based molluscicides to earthworms
Edwards et al, Ohio State University

I expect some of those that read these papers point out that some research was not carried out under field conditions, and that high rates of EDTA was used in one case. This is true. But that is also true when many medicines are tested and doesn’t change the facts that EDTA is toxic to earthworms.
As for high dosage rates, it is my experience, from teaching FEPA courses, that those spreading pelleted materials often overdose at significant rates. This is especially true in the case of gardeners who frequently spread pellets at rates far in excess of the recommended doses. It’s hardly surprising when they haven’t been trained and have no reference point on which to base their application rates.

Image Attribution: James S.W., Porco D., Decaëns T., Richard B., Rougerie R., Erséus C.CC BY 4.0, via Wikimedia Commons

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