Slugs on the ground, slugs on the ground; you can’t see your beets cause you got slugs on the ground!

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Introduction

Slugs and snails introduced to North America from other continents, most notably Asia and Europe, have overpowered the indigenous – and relatively harmless – varieties. Snails carry a shell made of calcium on their backs into which they can withdraw at will. This spiral shell is added to as the snail grows and this process of gradually making the shell larger is the cause of the spiral shape. By the way, their shells are one of the examples of the Fibonacci mathematical series appearing in nature.

Slugs also have a shell of sorts, but it consists of a small plate inside of their bodies and is not visible. Both travel by means of wavelike contractions along a single foot that is kept lubricated with a slime produced by a specialized gland near the front of the foot. Most of the time, this slime is relatively thin, but when threatened the slime becomes thick and foul-tasting. (Another reason not to answer suspicious help-wanted ads in college towns.)

Generally speaking, when I use the word “slug”, snails are included by inference since, from the perspective of a gardener, they pretty much occupy the same biological niche. They eat pretty much the same foods. They succumb to pretty much the same poisons. They share, to a large extent, the same natural enemies and so on.

Damage

Where the destruction is incomplete, snails and slugs leave smooth-edged irregularly shaped cuts and holes in leaves. Typically, however, destruction is complete back to the nearest tough stem and may proceed over the course of sequential feedings until the leaf, or even the whole plant, is gone. Damage typically starts at the lower portion of a plant and works its way rapidly upward.

Identification & Biology

Description

Slugs can vary from the very short to over 10” and from nearly a pure black through various shades of gray and yellow. There is even a white variety. The most common form found in a garden are gray and about one inch in length. They cannot bite you and they are not poisonous to touch. They cannot dial a phone, so they can’t call their attorney. They are safe to do battle with. Slugs are hermaphroditic, that is, each slug has male and female sex organs. However, they are not self-fertile. They must meet up with another slug to exchange sperm.

Development

Slugs start life as clear eggs about 1/4” in size laid in clutches of up to around 150. As they mature, the eggs get cloudy in appearance.

Physical Evidence of Presence

There are two physical evidences of their presence; slime trails and actual damage. Slime trails will appear in the morning as fragile pathways that look for all the world like a an incredibly thin piece of crystal across your garden soil connecting the place where the slug entered your garden to what ever plant it ravished. Slugs will follow existing trails to find food and mates.

Virtues

No form of life will occupy an area unless circumstances are suitable. That is, if it is to prosper, there must be food, a source of water, sites for mating and reproduction and either an absence of, or shelter from, natural predators. Therefore, if you have slugs or snails in your garden, these conditions are present and the molluscs are serving some purpose. Snails and slugs eat fungi and garden waste (especially such as have been colonized by fungi or molds), lichens and leaves. So, three out of four of the items on its menu actually favor the gardener by returning nutrients to the soil at no loss to the gardener.

It is in the fourth diet choice, leaves, that 100% of the damage to a garden from slugs occurs. I know from experience that a rampaging herd of ravenous slugs can clear a stand of bell peppers in a single night. If they get as far as the growing tip, the plant is as good as dead.

Management

No matter which management choice you make, be sure to weigh it against possible adverse effects on desirable insects, earthworms and so on. A heavy hand, with ANY of the possible responses to a slug infestation will have an adverse effect on some other species. For instance, the same sorts of shelter that slugs prefer can also shelter their natural enemies. So cleaning out ALL the possible slug habitats will also send ALL the predators that utilized those spaces running.

Observe. Think. Act. Observe again, think again. Act again only if warranted. Keep the Pareto principle of 80/20 in mind, too. Twenty percent of your action will likely account for eighty percent of your results and in the garden an 80% solution is often more desirable than a 100% fix. Eighty percent solutions leave enough prey to keep predators nearby.

Garden Hygiene

The only thing in a garden should be the garden itself. Okay … maybe a fountain, too. And a place to sit. And a bird feeder and maybe a nesting box. Or two. But get rid of weeds, planks, non-essential stones and dense ground covers such as ivy in the garden and nearby. These all provide shelter for slugs and they will travel from shelter to food while you sleep. Good garden hygiene is effective in preventing or mitigating so many problems (weeds, diseases, fungal infestations, pests) that it is an essential element of any good garden. I’m not saying that your garden can’t have gracefully flowing lines … only that it should be clean; that is, cleared of anything which does not actually add to its value.

Cultivation Practices

Keep low-hanging leaves and fruit off the ground, preferably several inches up. If you find slugs (or earwigs) inside tomatoes, it is generally because the tomato was growing within reach of the ground, usually in direct contact with it. Pull the tomato and, depending on your ‘yuck’ quotient, either cut off the affected part and eat the tomato or give the whole thing a toss into an active compost pile. Ditto for other damaged plant parts such as beans or lettuce that has been munched on. To avoid certain types of fungal infections it is generally best to prune tomatoes about a foot above the ground and to apply a light mulch about one inch thick beneath them to prevent splashing. This formula is also a deterrent to slugs.

This light mulch is only sufficient to prevent splashing. To conserve moisture in the soil, apply mulch 3-4” thick. Depending on the type of mulch, you may need to top it off as the season progresses.

Fall tilling. If you live where the ground freezes over the winter, there are several reasons to turn the ground once more after the soil turns cold (but before it freezes) and about half of them have to do with exposing the eggs of pests to the coming harsh weather. Any earthworms that are exposed will be able to dig back to warmer depths, but eggs don’t move on their own. Below ground they might freeze, but they wouldn’t dry out. Above ground, they also dry out. The adults typically only lay eggs above a certain temperature (according to individual species), so most of the destroyed eggs will not be replaced. The adults will find their refuge again and start laying new eggs once the soil has warmed. By then, the predators will also be present.

Whether to rototill, plow or dig by hand is a matter of personal choice and much debate. What is certain is that if the soil is allowed to remain completely undisturbed, it will harbor more slugs than if the top few inches are disturbed in the late fall. This, however, must be weighed against the harm caused by destruction of the soil profile. One option is to apply a product such as Sluggo or Escargo in the final month before a hard frost. This will kill the adults and prevent the eggs from being laid.

Elimination of Refuge

Having accomplished the essential steps of hygiene, you will no doubt find that there are areas in and near the garden that offer refuge to slugs and snails but which cannot, like the underside of a plank fence or a water meter, be removed. These areas will require special attention, usually in the form of a trap, barrier or mechanical removal, although introduction of a predator is not ruled out. At least consider the possibility of letting chickens or ducks take care of these areas for you. Some cities will permit you to have a flock of hens so long as you do not keep a rooster. Since the eggs laid won’t be fertile, you can replace the hens as they age with mail-order chicks. Detroit does NOT allow ‘farm animals’ of any sort even though there are so many vacant lots in some areas that a good sized family farm could easily be established. I really don’t see how Rottweiler’s are an improvement over chickens or ducks … especially given the reputation of ducks as being effective burglar alarms.

Alternatively you could paint these areas with Bordeaux mixture in latex paint or place a trap (described below) nearby.

Handpicking

When slugs are ‘in season’, heading out into the garden armed with a flashlight, chopsticks, rubber / plastic gloves or tweezers to pick them and a bucket with a bit of ammonia water in it (be as humane as possible, make the solution fairly strong … perhaps 25% ammonia … so that death is at least quick) to serve as ‘the bucket of doom’ can be time well spent for the gardener. On a good night, it is relatively easy to harvest several hundred of them and feel virtuous about avoiding the use of any pesticides. When you get done, add enough water to fill the bucket and thin out the ammonia. Then pour the contents of the bucket on top of your compost pile and feel good about not wasting a bit of nitrogen. That’s two ‘wins’ for you; none for the slugs. Ammonia and decaying slug bodies are both good sources of nitrogen.

Traps

Traps for slugs generally take the form of refuge, except that the slugs are invited guests. Pieces of carpet of perhaps 18” square, or planks of 12” width and at least as much length work well. So do cabbage leaves laid on the ground or citrus and melon rinds placed upside down. The slugs will congregate beneath these in order to conserve moisture during the day. This makes it easy to destroy hundreds of them at a time. Just visit the traps in mid-afternoon and dispatch them by crushing, spraying with ~5 – 25% ammonia solution, or dropping them in a bucket of sudsy water. Don’t forget to add them to your compost pile no matter how they meet their doom.

Barriers

Copper foil

Copper foil may work because of a galvanic response shorting out the slugs electrical system or simply because the slug recognizes poison when he encounters it. In either case, the slug will leave it almost immediately. If you are going to use foil, make certain that the pathway is completely blocked and that the barrier is buried about 4” below the surface to deter burrowing slugs. The area protected must first be cleared of its existing slug population, or you will have simply trapped them inside with your plants. That’s a big ‘win’ for them, a big ‘fail’ for you.

Bordeaux mixture ( Latex paint)

Bordeaux mixture is a combination of copper sulfate and lime. (Follow the link for mixing and use directions. Commercial preparations sit on the shelf too long. Make your own.) It was developed for use against fungus in the vineyards of Bordeaux, France although it is quite likely that the Romans were using a similar mixture previously. Treat Bordeaux mixture as if it were poison. It is. Bordeaux mixture can reportedly be mixed with latex paint to retain its effectiveness for up to two years. I’ve not seen any ratios given, although it might make sense to just substitute the paint for the water in the linked formula. The copper sulfate would turn the paint blue, so be prepared for that color and let it serve as a reminder to you that the blue surface is, in fact, poisonous.

Abrasives

Builders sand, coarse sandpaper and shingles (applied like copper foil), ashes, diatomaceous earth, volcanic rock, coke clinkers and the like are all said to be effective. However, there are nearly as many reports of failure with them as successes. Nearly all of them fail as soon as they become wet and the diatomaceous earth is far more likely to kill helpful insects (it enters the joints between their body parts and cuts them up on the inside) than it is to have a noticeable effect on slugs and snails. Slugs and snails are quite capable of crawling over the edge of a razor unscathed, so you can decide for yourself how much of a barrier a piece of coarse sandpaper might be.

Caustics

Wood washes are said to work well so long as they remain dry (there’s that water problem again) but the exact mechanism of control is not well known. Dry wood ashes would consume enormous amounts of the slime slugs make and, as it was wet with the slime, would also have a caustic effect on the exposed skin of the foot. Having once stood in my underwear in a railroad yard to get caustic soda rinsed off me (caustic soda perspiration = a very bad thing), I can appreciate how a slug, unable to promptly rinse off, would be cautious about crossing a line of wood ashes. If you choose to use ashes, you’ll need a band at least 3” wide and 1” thick completely around the area to be protected. Since rain or an overhead watering will undo its worth, you’ll need to keep applying it and this will tend to render the soil where the band is located inhospitable to future plant life.

Natural Enemies

Poultry

Pretty much any fowl that will dig an inch or so deep into the soil will dispatch any slugs or snails they find. The key is to attract them to your garden while protecting your seedlings from destruction. Ducks and chickens can be moved around the yard in what is called a “Chicken Ark” … basically a homemade wheelbarrow with a coop at one end and a floor-less enclosed area at the other. You can let them peck and scratch in an area for a while, then move them somewhere else while that patch of lawn or garden heals. Lather. Rinse. Repeat.

Beetles (black beetles, devils coach horse)

I’ve never seen a devils coach horse in my garden and if I did, I’m sure that I would be afraid of it on the first encounter. It’s HUGE. However, it is a member of a larger family of beetles known as the ‘rove’ beetles for their habit of roving about. They are to be encouraged in your garden. Perhaps the topic of how to encourage beneficial insects would be fit grist for a future article.

I have, in South-east Michigan (USA), seen black beetles from time to time. Considering that my own personal garden is only 240 square feet, I’m not surprised that such sightings are rare but, instead, I am delighted that they are present at all. The only thing I’ve done to encourage them is not to apply poison to my garden for the past 20 years except for narrowly defined purposes. In the past ten years, I’ve applied only caffeine and bT. I’ve learned to prevent most fungal infections with compost tea. It’s not perfect, but it’s not poison. And, while also nourishing my plants, it can’t kill any of my insect helpers.

It wasn’t until I saw a photograph of two earwigs hanging on to a slug five times their size for all they were worth that I realized that they had a position in the food chain that didn’t include eating my tomatoes. I may never see such a battle in my own garden, but I sleep a little better knowing that it probably goes on without me to referee.

Decollate snail

This guy is used in some counties in California in order to protect the citrus crops from snails. Decollate snails are carnivorous and cannibalistic, munching on small snails only. Since they don’t bother with larger adults, some will always escape their attentions … which is the proper situation for maintaining a predator population.

Slugs also are food for wildlife, including raccoons, possums, garter snakes, toads, turtles, frogs, lizards, lightning bug larvae, and birds. While none of these will totally eliminate slugs and some, such as raccoons and possums may cause more damage than they prevent, to the extent that these are present, the slug population can be reduced without need for poisons of any sort. Sometimes birds will peck at tomatoes in an attempt to get a drink. You can virtually eliminate this by having a saucer of fresh water nearby. One simple way to do this is to simply let the end of either a drip or weep irrigation system drip into an inverted pail lid at the end of its run. Just let the last few inches overhang the lid by a few inches, allowing it room to drip. Birds are especially attracted to moving water, but a steady drip is all they insist on.

Baits / Poisons

Slightly moistened dried dog food works well as a bait and is non-poisonous if Fifi or Fido decides to eat some. Just scoop it up with a pooper-scooper or shovel and toss into the compost pile in the morning. (Note: in the city, always cover fresh additions to a compost pile with a little hay or sawdust. The police will respond to complaints and, if they find fresh stuff on top, will write a FAT ticket for rat harborage. After you have already lost a days work to go downtown, you can try to explain how compost piles work to the judge. But, be prepared to give the best speech of your life … in Detroit the first ticket is $10. The second is $250. The third is $500 and the fourth time is considered a bonus round. If you lose this time, the county supplies free meals, laundry and lodging for a month or more. They will also supply you with a room mate covered in tattoos.

I am including the following chemical preparations for the sake of completeness only. Their inclusion on this list does not imply any sort of endorsement. Indeed, if you have any ambitions of growing your own food according to organic standards and methods, they are forbidden. I have marked the non-organic compounds with maroon lettering.

I’ll try to give a brief explanation of why they are ‘verboten’, but this article is not the place for a dissertation on the subject. Just take my word that any productive garden requires a wide array of biota at, above and below the soil line and anything that kills indiscriminately is to be avoided like the black plague. It may be necessary, under certain circumstances, to use these chemicals. Typically, this is in the first year for both garden and gardener. By the second year, both the gardener and the garden should be in a much improved state no longer needing these drastic measures to obtain satisfactory results. Keep in mind that every garden and every gardener has an ‘off’ year from time to time. That’s why we preserve the excess during the good years.

Metaldehyde

http://pmep.cce.cornell.edu/profiles/extoxnet/haloxyfop-methylparathion/metaldehyde-ext.html

Metaldehyde was originally sold in a highly concentrated form as a sold fuel in Europe. Its use as a pesticide was the result of a chance observation that slugs fled areas near where the tablets accidentally fell. For use against slugs, it is reformulated to either a 2% or a 4% concentration. In the reformulated state, it is bound with grains and molasses. As the grain begins to ferment naturally, the slugs are drawn to eat it and the metaldehyde that is bound to it. The 4% formula is far more lethal to the slugs, but it is also far more lethal to dogs, cats, wildlife and small children. Take care, also, to avoid contaminating ponds or waterways with it. To avoid accidental ingestion, keep pets and small children away from treated areas and also avoid getting the product on plants, especially leaf surfaces.

Metaldehyde is normally sold in a pelleted form. Do not concentrate the pellets: scatter them. When concentrated in an area, they are much more attractive to small animals as food … who are also far more likely to be able to take up enough to obtain a fatal dose.

Metaldehyde is not especially effective against slugs so it is also frequently combined with some form of carbaryl (if you see the letters ‘carb’ in it, steer clear). The carbaryl is included to give the metaldehyde a better chance of killing not only slugs, but also other insects in the ground, such as ground beetles. The problem with that is that the ground beetles are ALSO working to control the slugs … and other pests, as well. They are WANTED in the garden. Any preparation containing carbaryl will also kill your earthworms. Earthworms are so valuable to a gardener that the loss of any by an act of the gardener is not to be tolerated.

Mesurol (or Draza)

http://www.entomology.umn.edu/cues/mnla/mesurol.pdf

Mesurol is intended for use only in greenhouses where a nearly sterile environment must be maintained because an ecologically balanced environment cannot. It has a high kill rate on slugs and snails and long-lasting residual power. It is also one of the class of chemicals known as ‘carbamates’ and is therefore lethal to the earthworms. It is labeled against use on food plants … so keep it out of your garden!

Iron Phosphate (Sluggo, Ferramol, Ferro or Escar-go)

Iron phosphate is actually useful as a fertilizer if applied sparingly. Gradually it will break down into iron (good for plants, good for you) and phosphorous. The phosphorous will form phosphoric acid, which, in moderation, helps maintain the pH of the soil in a desirable range. It is sold, pelleted with a grain base, as poison for slugs and snails under various brand names, Sluggo and Escar-go being among the better known. DO NOT USE any product containing EDDS or EDTA (Sluggo, for instance). These added ingredients are more deadly than the iron phosphate, do not occur in nature and are not acceptable for organic purposes.

Fresh coffee grounds

A few years ago, while researching my own slug problem, I stumbled across some research from the University of Hawaii about some sort of frog that was giving them grief in the sugarcane fields. Lacking sufficient natural enemies, the little lads were, so to speak, raising Cain in the cane fields. Most poisons were out of bounds because sugar cane is a food crop. Trapping was a waste of time … things were a mess. Then someone applied a carefully metered scientifically scientific bit of caffeine to the skin of some of the frogs. Almost instantly the frogs died.

I didn’t have any problems that looked like a frog, but I did have one that had direct contact with the environment through its skin. Like the frog, its central nervous system was unaccustomed to that early morning jolt most of us look forward to. So, lacking time to set up a carefully metered experiment with control groups and GPS coordinates and all that fancy scientific stuff, but desperately needing to effect a dramatic reduction in the slug population of my garden, I went to a nearby store and bought a can of the cheapest coffee I could find. It is actually important that you buy the cheapest … try the cheapest offering at a warehouse club. These are the “Robusto” beans and they have a significantly higher caffeine content than the better flavored, but more expensive, beans. Then, that afternoon I spread the contents of the can rather liberally over about 1/3 of my garden. In the morning, the protected portion of the garden had no new signs of damage whereas the rest of it looked even more raggedy than the day before. So, off to the store I went for several more cans … enough to apply it liberally over the entire garden at once. That ended my slug problems for that year … and the next. The residual effects seem to last long enough to wipe out at least the next 2-3 hatchings of slugs, dramatically eliminating the number of breeding-age adults. Last year I saw signs that they were returning in significant numbers again, so I’ll apply the coffee again this year. If you intend to copy this, note that the grounds have to be FRESH. Used grounds do not contain enough caffeine to be effective, nor does brewed coffee. Based on the UoH study, even fresh grounds walk the fine line between a slug having a sleepless night and slipping off into eternal sleep. (Note: if you have used grounds, put them in the garden, too. The slugs won’t care, but the plants and earthworms will appreciate your generosity. And the garden will smell good, too.) I do not think that the slugs have to actually eat the fresh grounds and, since it would be a totally unfamiliar food, I don’t see why they would. I am of the opinion that the caffeine is able to pass through the slime and derma and therefore I spread it so thickly that they MUST encounter it on the way toward their targeted food source.

You can also make Quack Grass pellets by mixing together 1 oz of corn meal, ¾ oz powdered milk, an oz of cornstarch and 16 oz of beer. Add to this 8 oz of dried and finely chopped quack grass including stems and roots (make certain, by baking, that it is totally dry / totally dead). This should leave you with a thick paste. If it does not, add additional rounds of the dried ingredients until you DO get a thick, barely stirrable, paste. Run this paste through a meat grinder to form pellets and allow them to air dry. Sprinkle the pellets generously around seedlings and other plants that slugs target. In some tests this has been shown to effect near total control of adult slugs within 30 minutes and to remain effective for about a week. Presumably, weather had reduced the effectiveness and a new slug population had hatched from eggs. My source did not cite the original test results, so no link for this.

Repellents

Rosemary leaves, sprinkled about, are said to work as a repellant, as are finely chopped quack grass leaves. Do exercise caution, however, not to include living quack grass roots in your garden or you will be fighting them for a very, very, long time.

Trap Crops

One of the great values of a trap crop is that you can lure a pest to a specific location where harm to the garden is minimized while hazard to the pest is maximized. Predators follow prey. So it stands to reason that if you concentrate prey in a location you will also concentrate the corresponding predator. This is one of the corollaries of the organic concept of controlling damage but not eliminating its causative agent. Once the pest is gone, the prey moves on, too. The the pest will always return ahead of the predator. However, if some of the prey remain, some of the predators will also remain and, should prey become abundant again, it is a simpler matter for the predator population to increase from an existing population base than it is to start from nothing. For slugs and snails, a small stand of tall grass will serve as a trap crop. It provides both a place to hide from predators and also a place to hide from the drying effects of the sun.

Lures

Lures are similar to trap crops in that they draw the slugs and snails to a location where they will cause you no damage. Traps for slugs and snails work by luring the wee-beasties with scent. The problem with these is that putting the traps in your garden will send out an invitation to every slug within 100 yards of the trap. The ones from your own garden that fall for your tricks will be replaced … and more … with other slugs in the vicinity. This is not good. The answer to this is to set the lure some distance outside your garden. It is sufficient to pour stale beer or spread a handful of corn meal over the fence into your neighbors lawn or in the alley some distance away. The idea, of course, is to get the slugs already in your garden to give it up for a greener pasture.

Relax

Slugs and snails have been around since before mankind began to practice agriculture. They are likely to be here long after you and I have left this scene. So, go ahead and fight the good fight … but steel yourself, victory is not measured by completely banishing slugs and snails. That would leave their biological niche unoccupied and a healthy garden is one that is fairly teeming with all sorts of life. No; victory is proclaimed the day you step into your garden, coffee cup in hand, and the damage is hard to find and in all your garden the slime trails are both few and far between.

– Bill