Of course you should use mulch, everywhere you can. Mulch does numerous things. It keeps soil pathogens from splashing up onto your plants in a heavy rain. It greatly reduces evaporation. It helps stop cut worms and it will become compost among other things. And slugs like to crawl around on dirt not wood chips or what ever your mulch may be. You have slugs get the organic remedy. It is called SluggoPlus
Iron Phosphate Slug Bait - How Dangerous is it in the Garden?
by Bill Meyer
A few years ago a new type of slug bait began appearing on the market. Instead of the tried and true metaldehyde baits that had been in use for quite some time, this new bait used iron phosphate. This new product has made significant inroads into the market, riding on claims of being "natural" and safe to use around pets and wildlife. A quick check of the EPA's info on iron phosphate seems on the surface to back up these claims of safety, but is that the whole story?
Much of the claims about the safety of this product are based on the fact that iron phosphate occurs widely in nature. It is also used in vitamin supplements. It is a safe compound that is not easily digested so does not easily release iron into the system if ingested. The EPA seems to just give these products a pass without insisting on further testing because of this, but I began to wonder what would happen if a dog or even a child might ingest a large amount of this product. Like the metaldehyde baits, it is in a bait form that is attractive to pets and maybe even to small children.
Like metaldehyde baits, these iron phosphate baits are mostly a food-based pellet that smells strongly like cereal to attract the slugs from a distance. Unlike the metaldehyde baits, the iron phosphate baits do not appear to contain Bitrex to prevent unintentional ingestion by pets and children. Bitrex is an extremely bitter-tasting substance that most mammals will not eat. The EPA recently mandated that metaldehyde bait products sold in the U.S. increase their Bitrex amount tenfold to reduce the risk of accidental poisonings. Iron Phosphate baits like the popular Sluggo do not list Bitrex as an ingredient, and are not required or presumed to have it.
The marketing campaign by the companies that sell iron phosphate slug baits is full of statements like "doesn't harm pets and wildlife" and "no danger to dogs, cats, and birds" and "not harmful to beneficial animals, such as earthworms and frogs". These exact statements are found in a brochure directly from Neudorff, the manufacturer of these baits. Retailers seize on these claims and sell the product with enthusiastic claims like "safe and non-toxic" and "safe around children and pets". They also target the organic-lifestyle crowd with claims of being "all-natural" and "completely organic". The label on the product lists only iron phosphate as the active ingredient, and "inert ingredients". The dubious organization NCAP (Northwest Coalition for Alternatives to Pesticides) says the following "According to a phone call to NCAP from the company that manufactures iron phosphate slug bait, there is only one “inert” (unidentified) ingredient in these baits, wheat gluten.
My first thoughts on seeing the marketing for this product were to wonder if it was indeed as safe as its proponents were claiming. A quick look at data from the EPA was oddly inconclusive, as they say "no testing required" in several key areas because of iron phosphate's common presence in the environment and low solubility. Essentially iron phosphate will pass through the digestive system largely if not completely unchanged, making it pretty harmless in truth. A bait made up of iron phosphate and (if NCAP can be believed) wheat gluten would in fact be as safe as it is advertised to be. It would also not kill slugs or snails, and would rot much quicker than it seems to do.
The first signs that it is not all that safe have begun to appear. Dog poisonings are being reported and two recent studies concluded that normal usage kills earthworms. The Ohio State study says the EPA reports "5 domestic animal deaths, 8 major domestic animal incidents and 106 moderate and minor domestic animal incidents from the use of iron phosphate slug and snail baits" as of 2008. Since iron phosphate itself is a pretty harmless substance, something just wasn't adding up. When I found the Ohio State study I found out what it was that was missing from not only the advertising but from the label itself.
Iron phosphate is non-toxic to both humans and dogs, as well as other pets and wildlife. Studies also show that it is equally non-toxic to slugs and snails, because it does not release its load of poisonous elemental iron very easily. If this is the case, why do other studies show that it is a very effective product that rivals the metaldehyde baits? How can these baits made of nothing but iron phosphate and wheat gluten be as effective as they are shown to be when other studies show that snails can live indefinitely on a diet of iron phosphate?
Enter a man-made chemical called EDTA, a chelating agent that causes the iron phosphate to release its elemental iron easily in the digestive systems of not only slugs and snails but of pretty much anything that eats it. EDTA or the similar EDDS are the
only reason these baits are effective, yet interestingly the label only reads Active Ingredient: Iron Phosphate - 1%, Inert Ingredients - 99%. No mention is made of the presence of another chemical that can turn harmless iron phosphate into a deadly poison. Apparently EDTA was slipped through the cracks in our regulatory system as an "inert" ingredient, and inert ingredients do not have to be listed on the label. Since iron phosphate is harmless, and EDTA is the ingredient that makes it effective, not to mention dangerous, something is really wrong here.
Missing from most of the literature about iron phosphate slug baits is their mode of action - the "how" of what they do. Some trying to write about them even say that the mode of action is not well understood. Once you know that EDTA is present in the bait, the mode of action becomes clear pretty quickly - iron poisoning. In Australia, these baits are labeled as containing EDTA. An article about them contains the following mode of action description:
"Iron chelates can be incorporated into bait, which is palatable to the mollusc and it appears that at an appropriate location in the mollusc's gut the iron is released as Fe3+, and is toxic causing death if the concentration is sufficiently high. A number of chelates are efficacious, particularly those belonging to the group of compounds referred to as complexones, but to date the iron EDTA complex formed by the reaction of ferric EDTA with hydroxide ions is the most effective on the basis of the total iron concentration. A number of iron complexones have been shown to be effective."
A review of these products by the Swiss organic certification organization (FiBL) discovered the EDTA content and stated that these products were likely no safer than the metaldehyde baits, that EDTA itself was significantly more poisonous than metaldehyde, and even said they weren't even sure that it wasn't the EDTA alone that was killing slugs and snails. When I started posting the link to that study and warning people about these baits, the report was quickly removed from the website that hosted it. It is referenced in the Ohio State study, though. A graphic comparing the toxicity of EDTA and metaldehyde was also taken down.
The actual effect on slugs and snails does seem to be iron poisoning from what I can find. The referenced pet poisonings also seem to be the result of iron poisoning, from iron freed up from the iron phosphate by EDTA.
