Mastering Slug Control: Strategies for Gardeners in the PNW

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In this episode of The Evergreen Thumb, host Erin Hoover welcomes Diana Wisen, a WSU Extension Master Gardener, for an in-depth discussion on slugs and snails in the Pacific Northwest. They explore the ideal environmental conditions that make the region a haven for these pests, their biology and ecological roles, and the challenges posed by invasive species. Diana explains the feeding habits, rapid reproduction, and various plant preferences of slugs, as well as effective slug control methods, including mechanical removal, biological and cultural controls, barriers, and creative solutions such as using beer traps. She emphasizes the importance of early intervention, ongoing management, and developing a level of tolerance, since eradication is impossible. The episode ends with reflections on the resilience of slugs and snails, and the life lesson that sometimes, success comes from moving slowly and steadily.

• Slugs & Snails article by Diana Wisen
• OSU Article on Managing Slugs & Snails
• The Secret World of Slugs and Snails: Life in the Very Slow Lane by David Gordon
• OSU Article How to Control Slugs in Your Garden
• Integrated Pest Management Resources
• Skagit County Master Gardeners
• Facebook: WSU Skagit County Extension Master Gardeners

Erin Hoover (00:00)

Welcome to episode 70 of The Evergreen Thumb. My guest today is Diana Wisen. She is a WSU Extension Master Gardener in Skagit County. Diana is actually one of the very first people that I met when I started training as a Master Gardener. We’ve been acquainted for more than 10 years now.

Diana, thanks for joining me today. It’s great to see you.

Diana Wisen (00:23)

It’s a pleasure to be here.

The Slug and Snail Environment in the Pacific Northwest

Erin Hoover (00:26)

Today we’re going to talk about slugs and snails. And I know they are the pest gardeners just love to complain about. So, what makes the Pacific Northwest such an ideal environment for slugs and snails?

Diana Wisen (00:37)

We have everything that slugs and snails need to survive, lots of lush greenery, and lots of moisture. We have cool temperatures, cloudy days, and very frequently, our ground up here in the Pacific Northwest does not freeze in the winter.

It seems like slugs are particularly numerous this year. They could come out and start feeding at 40 degrees, and we’ve had very little weather below 40 degrees. So they’re very happy.

Erin Hoover (01:03)

I bet. Are there really more of them than you think, or are we just seeing them earlier than we’re used to?

Diana Wisen (01:09)

We saw them all winter, which is pretty unusual. I don’t know, it’s hard to say whether there’s more or not, but people are more aware of them as well. And we are seeing more snails than people who’ve lived here a long time ever remember, not yet this year. But I think our drier summers make it easier for snails to live, whereas slugs need more moisture.

Understanding Slugs: Biology and Ecology

Erin Hoover (01:33)

I remember when I lived in Anacortes, the snails were actually more prolific than the slugs.

So, slugs and snails, we think of them as slimy critters. They’re not insects. What are they? What class of animal do they belong to?

Diana Wisen (01:40)

Slugs are a member of the invertebrate family. They don’t have a skeleton, and they’re part of the phylum called Mollusca, which includes clams, squid, and octopus, all those kinds of things. And within that phylum, they are a gastropod, which means stomach foot. Of course, that perfectly describes what a snail looks like. And that’s basically what it is. They are basically a big, long intestinal stomach that crawls with a foot that’s a very muscular organ that enables them to crawl up walls, crawl across ceilings, all kinds of places. And they’re born to eat, that’s what they do.

Erin Hoover (02:31)

So most gardeners think of them just as pests, but do they actually have an ecological role?

Diana Wisen (02:38)

Yes, our native slugs really are; you rarely see them very much. They’re certainly not much of a problem. And they eat rotting debris. So that’s a really good ecological service that slugs and snails eat. We would be buried in leaf debris if it weren’t for them.

But it’s the invasive slugs that eat more than just rotting debris. They eat your lettuce and your potatoes and your dahlias, and that’s when it becomes a problem, when they compete with us for the same food.

Erin Hoover (03:12)

So how can we tell the difference between a native and a non-native slug? I know banana slugs are kind of the most obvious.

Diana Wisen (03:22)

In the home garden, you don’t see many native slugs. And if you do, they’re very small, and they’re not very noticeable. The native slug we all love is the banana slug. And those are frequently out on the Olympic Peninsula; you see them.

Around here, you would see them in woodland areas. You would rarely ever see a banana slug in your home garden. What you do see is the Chocolate Arion, the Limax Maximus, the leopard slug, the Gray Field Slug, those kinds of slugs. Those are the kind of ones that come into your garden, into your cultivated garden.

Native slugs are not much of a pest, really, in terms of the home gardener. They can be annoying, but they’re not going to eat the food that you’re trying to grow for your family.

Erin Hoover (04:09)

But slugs do eat a lot. You said they live to eat.

Diana Wisen (04:12)

Yes, slugs can eat four times their weight every day. Imagine if you and I ate four times our weight every day, day after day after day, but slugs eat a lot. That’s all they do is eat. So, they can compete.

I mean, I remember there were Puyallup strawberry farmers that got wiped out because slugs came in and nibbled on all the fruit. Slugs don’t stop in one place and just eat. They eat as they travel.

So, they can cause a lot of damage in that spot. They’ll just eat one bite, and they move on and can contaminate a lot of food that way.

Feeding Habits and Plant Preferences

Erin Hoover (04:51)

So what type of plants tend to be their favorites?

Diana Wisen (04:54)

Oh my goodness. I would think things like lettuce and your greens are really popular. They can burrow in as a tiny slug into a newly growing potato and live inside that potato, the potatoes whole life. And you open up the potato, and there’s this full-size slug. Art Antonelli once showed us a picture of a slug that he cooked a potato, he opened it up, and there was the slug inside. So they love potatoes.

They love dahlias and delphiniums. I think anyone who grows flowers in the Northwest knows they eat a lot of things like that. I’ve seen them way up in apple trees. They eat practically everything. There is a list of things that when I give this talk as a program. I bring a list of things that slugs don’t eat, but it’s things like artemisia and lavender and things like that. Though you can see slugs on those plants, but they may not eat them.

Erin Hoover (06:00)

You mentioned that the slugs move as they eat. So why does it seem like plants sometimes disappear overnight?

Diana Wisen (06:07)

Because there are several slugs. Banana slugs, you’re only going to see one. But these common slugs that we see, the garden slugs, there are a lot of them, and they hide underneath the plant, and they come out, and they eat all night long. So if your dahlia is just starting to come up out of the ground or your new lettuce is just starting to come up out of the ground, they can eat all of that in one night. And there are lots of slugs, not just one.

They lay 50 eggs at a time, and those eggs hatch within a few weeks, and they set out to eat. There are other things that eat food, too, or eat plants. The cutworms eat some of the things, and so if something is totally disappearing over a week, it might be something other than a slug, like a cutworm or both. Both cutworms and slugs love rhubarb. So it’s pretty hard to tell which is which.

Slugs kind of shred things as they go, whereas a cutworm will stay in one place and just eat, eat, eat.

Erin Hoover (07:11)

So, how do slugs actually feed? I understand they have lots of teeth.

Diana Wisen (07:17)

Slugs have what’s called a radula, which is a set of 27,000 teeth. And they shred things as they go along. How they find their food is really interesting. We make fun of the slime, but the slime is really one of the reasons that slugs are so successful. They have those little tentacles, and they can’t see other than light and dark with the tentacles.

But the tentacles also have a really strong sense of smell, and their slime is like their messenger. They tell each other that they can smell, there’s good food ahead, or there’s possible bait ahead of us, or there’s danger ahead of us. So the slime is how they can sense there are good things to eat or other good things or a warning system.

The slime also protects slugs because you can see slugs going across the driveway, or gravel, or things like that. They will produce extra sturdy mucus that will protect the slug. I had a picture of a slug climbing over a razor blade. So things like egg shells, diatomaceous earth, those things really don’t prevent slugs from eating your plants if they can smell good food ahead.

And slugs hide during the day, and on dry days, they will hide. They can go down as much as two feet to protect themselves. But during the day, they’re underneath boards, bricks deep down in the soil. Then it gets cool at night, and out they come. It’s been reported that only about 5 % of the slugs around are on the soil at any one time. So even if you do a clean sweep of your garden one night, they’re gonna be more the next day and the next day and the next day. So it’s an ongoing process. You’re never going to eliminate all your slugs and snails. You just try to get them into a manageable amount.

Erin Hoover (09:19)

Right. So how far can a slug travel in search of food?

Diana Wisen (09:24)

I guess they have reference of slugs going 40 feet in a night or more up over a wall and back down. It’s life in the very, very slow lane, but it’s very successful. You don’t have to move fast to find food if you’re a slug.

Erin Hoover (09:40)

Slug Reproduction and Lifecycle

How do slugs reproduce? What does their life cycle look like?

Diana Wisen (09:45)

This is quite fascinating to people who have no idea. Slugs have a very active reproductive life. Slugs are hermaphroditic. It means they have both male and female organs.

They can reproduce several times in a lifetime. Some slugs only live a year. They can live up to six years. The average non-native slug probably lives two to three years. And they can mate and lay eggs several times a year. Both the male and the female can lay eggs because they both have both kinds of organs. They can lay anywhere from 50 eggs; sometimes, there are as many as 500 eggs in a season. Imagine if you and I had 500 babies in a year.

So they are, slugs are very successful because they have discovered how to survive, and having lots of eggs is one of the ways. And eggs are laid in damp soil, often an inch down, but sometimes just under a brick or a board. The eggs look like tiny little pearls. Sometimes they’re clear, sometimes they’re kind of creamy, and sometimes they’re the color of skim milk about the size of a pinhead.

Some of them hatch within a couple of weeks, three weeks, and some of them overwinter. If you have a plant like a chrysanthemum plant out in your patio that you didn’t ever really put in the ground, if you pull it out of the container right now, I bet you’ll see little tiny clear pearls on the side of the container. Those are slug eggs.

Slugs rate zero as a parent. They lay the eggs, and they go away. That’s the end of that. But the slug is able to grow and hatch and take care of itself right away.

Handling and Managing Slugs

Erin Hoover (11:37)

Are there precautions that gardeners should take when handling slugs?

Diana Wisen (11:40)

Yes, most people don’t want to handle slugs, so that’s pretty good in the first place. But after a while, sometimes you get used to touching them. And then I realized one shouldn’t because slugs can carry parasites. They can carry bacteria, such as Salmonella. So you should not touch slugs with your bare hands. Always wear gloves.

If you do touch slugs and you get the slime on your hands, the slime is an amazing thing. It actually absorbs moisture. So if you would try and wash your hands, you get more slime. You’re increasing it. So you rub your hands with a dry paper towel or dirt or something like that to get the slime off your hands. And then you can wash them and wash them really carefully to disinfect them.

Can we talk about slug management?

Erin Hoover (12:29)

Yeah.

Effective Slug Control Methods

Diana Wisen (12:31)

Okay, yeah, that’s what people want to learn: how do I get rid of them? And you’re never gonna get rid of all of them. We don’t need to eradicate. They have their space and their place in the web of life. But one of the first steps would be simply to think about their lifestyle. When are they the most vulnerable? Like most anything, it’s when they’re very young, when they’re very tiny. So the first thing you do is try to smash those slug eggs, and that’s considered a mechanical way, you’re smashing them.

Or maybe birds can eat them. Birds eating them would be a biological control. Something eats the pest. However, not many things like slugs.

Snakes, toads, frogs, and some birds will eat slug eggs and tiny slugs. People say, ” Oh, birds eat them”. Well, birds do not like big slugs. None of us would. They would gag on the mucus. Someone always in the audience always says, well, geese and ducks will eat slugs. And yes, that’s true.

But the poultry solution is not for everyone. If you ever had a duck or a goose in your yard… I’ll take the slugs over the mess that geese and ducks could cause in a yard. biological means that some predator eats the slug. Cultural means that you keep the area drier, because slugs need moisture, so keep things dry. Remove things that they can hide under, like, bricks. Plant things that slugs don’t eat, you know, there are things they don’t eat. So those are considered cultural ways.

Mechanical ways are very effective, and that’s like taking out a pair of scissors or a knife and slicing them in half. That’s a dead slug.

Beer Traps and Other Creative Solutions

Going out at night with a flashlight when they’re out and just going through your garden and getting rid of every slug you can find. Some people like to cut them in half, and some people throw them into a bucket of soapy water. Those are mechanical.

Barriers like putting a copper strip around your raised bed so their antennae hit the copper, touch the copper strip, and they get a little shock, and so they avoid it, and they back off. So that’s considered a mechanical barrier.

Keeping your pots up off the ground so they can’t get to them. They could smell that greenery up there. So they’re going to try to get to your pots. They can climb long distances. Just because you have a big livestock tank with your container garden doesn’t mean that the slugs can’t get up and get into your vegetables. So the copper strip is very effective, and it will last for several years, even when it turns green.

Or you can take two-liter bottles and cover your plants. Make sure for ventilation to kind of protect them.

Ways to protect plants: coffee grounds, diatomaceous earth, egg shells, and gravel don’t work very well. A really wide barrier of dry ground, like six feet all around your garden of dry ground can help prevent slugs. And then if you have a meadow or a large area, keep it mowed pretty low. That prevents more slugs from hiding there. It’s to create conditions that slugs don’t want.

The chemical methods are what people tend to turn to when all else fails. There are a lot of slug products out there right now. In the old days, we used to use Cory’s metaldehyde, and that is no longer available because it was poisonous to livestock, children, and birds and things like that. It’s not available anymore.

The iron phosphate products are very common now. They are safe to use. I remember once in the Northwest Flower Garden Show, a woman stood there and ate it all day long. I really don’t recommend that. But it’s iron phosphate, and it is safe to use around children and pets. The most common one is Sluggo, which is becoming almost a generic term for all of them. There are many brands out there, but it’s iron phosphate. And the way it works is the slug is attracted to it and eats it, and it affects the slug’s gut, and the slug stops eating and goes away to die.

But the problem with that is you do not see the dead bodies. And we like to see the dead bodies. But what happens, you will see in a few days, there’s no damage or a lot less damage. So that’s a really good thing. And there are other products out there. But as far as I know, the metaldehyde products are no longer available.

Don’t put the iron phosphate right up against your plant, because it has a lure, a scent that lures them in. And if they get to your plant, they might eat your plant before they eat the iron phosphate. And you sprinkle it very sparsely. A teaspoon will do a whole square yard. In the old days, we used to have these little slug-bait volcanoes all around our plant. But that’s not how you use this type of product. And it will last through the rain, but it does have to be reapplied after two or three weeks.

Erin Hoover (18:00)

Okay, what about beer traps?

Diana Wisen (18:03)

Well, people wonder if beer traps are a chemical approach, and no, they are not. You fill your cottage cheese carton with holes on the side or about halfway up with beer, and you set it in the ground so the hole is level, and the beer that slugs smell the beer, you need to put a lid on it too. The slugs smell the beer, the yeasty smell of the beer, and they come in, and they drink their fill and they drown.

They are not poisoned. Oh and with other slug baits, the iron phosphate, the slugs are not poisoned. They just stop eating. And if you don’t eat, you die. So don’t worry about that. But for the beer traps, they do work because they attract slugs. So you don’t have to go and hunt slugs down.

You provide the party and they come to you and they drown. It’s their own fault. And then the dead bodies attract other slugs. So more come. it does work. It’s very effective. You can’t use old flat beer. You can use beer that’s been sealed in its container for a long time. So you’ve got beer that’s old and you don’t want to serve. That’s okay. It just can’t be flat. And wine doesn’t work either.

Apple vinegar and hard cider, things that are fermenting, will work. It’s important to keep it covered because your dog will slurp down the whole thing and it can make your dog sick. So be careful about that.

And because dead slugs are so much protein, they smell really bad. Dead slugs smell really bad. So if you do one of these soapy water things or a beer trap, you need to empty it out and bury that mixture every couple of days. Otherwise, it really is very smelly. I don’t put it in my compost bin. Some places they tell you to do that, but I don’t do it. I just bury it.

How to Get Started with Slug Control

Erin Hoover (19:57)

So if a gardener gets overwhelmed by the number of slugs in their garden, what’s the first thing you recommend?

Diana Wisen (20:03)

Get started taking care of it. Don’t put it off. It depends on why you’re gardening and what you’re growing. If there are slugs, if you’re growing things and your garden looks okay and you’re happy, you just don’t like slugs, you can learn to live with it. But if you’re trying to feed your family, you need to get out there right away with a slug boat, with a knife, with everything you can do.

Don’t overwater.

Overwatering your garden, which sometimes, here in the Northwest, we water too much. Even though I know we have dry summers, but if your plants are deeply rooted, they can withstand a lot of drought. So don’t overwater because that encourages slugs. But like weeding, any kind of pest, you need to get on it right away. Start early. Don’t wait till you have a problem because there are slugs out there. They’re already feeding. So get started now. Which is true of any garden pest.

You know, you need to keep a handle on it and keep things at a level that’s acceptable to you.

Erin Hoover (21:09)

So what are the key signs that what you’re doing is working?

Diana Wisen (21:13)

You see less damage. That’s basically it. People who have gone out and chopped slugs at night.

You can do that every night of the year, practically, and there will still be slugs. So you’re never gonna get rid of them all. But if you’re trying to protect certain plants, that’s where you focus your attention. Sometimes you’ll put down cardboard and then come back the next morning or the next day and scrape all the slugs off and do that repeatedly. And when you see less slugs, you know you’re making progress, but they lay so many eggs you have to keep at it. It’s not a once-and-done kind of thing and it’s year after year.

Slugs are very successful at surviving. That’s why there are 93,000 species of mollusks.

Patrolling for Slugs: Personal Experiences

Erin Hoover (21:57)

That’s a lot. So you mentioned patrolling for slugs at night. Do you have any stories to share about slug patrols?

Diana Wisen (22:10)

Well, when I teach this class, it’s really fun because I used to own a farm in the San Juan Islands and we raised a lot of our own food as well as 150 dahlias. So my son and I used to go out at night with shovels or and our headlights and flashlights. And each of us would kill at least 100 slugs every night. We would do this for two or three weeks.

And of course, we never made 100 % progress, but we did cut, and these were the big black Chocolate Arions. They’re the ones that in the summer, you don’t see them this time of year, but in the summer they’re quite large and you touch them and they roll up into a ball. They come in black, brown, orange, and they eat a lot.

The Limax Maxima is the leopard slug that you, when you see it, it’s gray with black stripes and you realize, yes, this is the leopard slug. They eat plants too, but they also eat other slugs. So when I find a leopard slug in my compost bin, I leave him there. I figure he’s my friend, or she is my friend.

But some of the gray field slugs, they’re hard to see. They’re not much bigger than your tiny finger fingernail, and they’re under a leaf, and they’re just everywhere. It gets a little discouraging, I think, at times. And you have to learn to accept damage.

Erin Hoover (23:37)

Well, and that’s kind of part of what we teach is integrated past management is a level of acceptance or tolerance and before you manage.

Diana Wisen (23:42)

Yes, exactly.

Final Thoughts on Slugs and Life Lessons

Erin Hoover (23:47)

All right, so do you have any final thoughts about slugs or snails that you’d like to add?

Diana Wisen (23:52)

Well, in reading David Gordon’s book, I think there’s some good thinking about life in the slow lane. Slugs and snails and gastropods have thrived for millions of years, longer than us, because of life in the slow lane. They have adapted to that, and success does not always come to the fastest. Slow and sure, you know, I think in reading about slugs, that’s a positive thing that they can teach us. And I think it’s a good thing to think about. Life can be very successful in a slower lane.

Erin Hoover (24:33)

Well, thank you so much for being here today. This was great information.

Diana Wisen (24:37)

Well, it was fun to share with you, Erin. Thank you.