Oregon State University says that at concentrations as small as 2500 ppm (.25%) thyme and spearmint oils achieve 100% mortality on contact with slugs/snails. Using this calculator, I figure that at 1/3 of a fluid oz (USA) per gallon, or 2 tsp per gallon!! The OSU slug specialist interviewed thinks there will be residual repellent activity and that the oils should be readily approved for commercial use. I have seen slug killer/repellents on the market with these ingredients, but not with standardized concentrations...that seems potentially important for ecological impacts. Can one just spray this stuff around at 2 tsp/gallon without worrying about soil biology, bykill, bystanders?
The permaculture part of this is to plant these as barrier plants in your polycultures. I have already planted a lot of thyme, it grows best on hugels and in raised beds unfortunately, native soil has proven too wet for it. A creeping/groundcover variety that carpets, like it did at my college in MA, seems best if a culinary one exists. I'll try it on swales around trees vulnerable to slugs (so far, elderberry & serviceberry--lost all the latter's blooms last year). I'm reluctant to plant anything in the mint family. But I wonder whether barriers of thyme, with nearby cairns for snakes, could be two key passive controls for slugs.
In the long term, I've read that oak tree leaf mulch repels slugs. Ironic, considering the only oaks I've seen in WA/OR are growing in parking lots. I'm told it's too slow-growing to have much commercial interest, the only kind that really matters alot, anymore, so it's been routed in favor of more profitable trees. I wonder if that partially explains the plagues of slugs sweeping the PNW, hmm
EDIT: I had meant to add that at a certain scale, distilling one's own essential oils would be necessary for cost reasons. So raising thyme (and spearmint if you can contain it) would confer the double benefit of barrier/polyculture planting and a for-profit crop. At 1/3 of an essential oil bottle, 2 tsp would get you a gallon of slug killer for $3.30 USD. Depending on myriad factors, you might end up distilling.
Then I wonder about those economics. I keep trying to get into distilling essential oils but have, three times, hit a wall trying to find a reasonably-priced solid home setup. It could recover more of its own costs if it had multiple functions, like distilling spirits I suppose. But there is so much chicanery in that market, I never get to pulling the trigger. I'm gonna look on permies for discussions of it. :)
Ha great! When i started my vegetable patch there were a lot of slugs and snails, eating a lot of my lettuce and young plants. Since i dug a pond which attracted frogs and salamanders there are less. As well i've noticed an uptick in the occurence of glowworms (lampiridae) which eat snails, surprisingly. I had no idea thyme plants repel slugs. Good news , i have made hedgerows around my beds, unaware even of the fact they repel slugs. All the flowers to attract insects and then birds might also have had a positive impact in mysterious ways, creating an equilibrium less supportive of a huge slug population.
I've got a little set to distill herbs, but it only really does give oil when i cook lavender. Rosemary and sage give this wonderful smelling hydrosol, which is a lot milder. When distilling herbs came about in the middle ages they got rid of the oils floating on top, it was regarded as way to strong. The watery substances were used, which contained the oils that were soluble in water. Makes sense since we are water mostly. I haven't had enough thyme to find out if my distiller will provide me with thyme oil or only with hydrosol, but i'm on schedule to have enough next year to try a batch. People have big distillers on you tube, a lot of money for not that much oil it seams to me. I understand you're hesitant to invest.
Thyme is anti microbial, my book mentions staphylococcus aureus,e coli, streptococcusfaecium, pseudomanas aeruginosa,bacillis subtilis, salmonella typhimurium, clostridium botulinum and antifungal Aspergilus ssp, cryptococcus neoformans. That book is focussed on what's in humans, a phytotherapybook, so i don't have accurate information on soils. If you spray it lightly, it won't penetrate that deep into the soil immediately, and how long does it take to evaporate, oils can be volatile, spray in the evening maybe.
I've learned to save lettuce seeds, and keep replanting, but on a big scale farm that's not do-able.
The university link i could not see, because i'm in Europe, a digital wall didn't take a government shutdown apparently,so if my answer is not appropriate, insufficient scientific or anecdotal i apologize but blame the internet.
Creating edible biodiversity and embracing everlasting abundance.
Thanks Sebastian. I'll try that first. Macerate, steep and strain. I'd ultimately like something that could be dispensed with a pump sprayer in a fine mist (and possibly, at higher volumes, with a backpack sprayer), so keeping solids out is key.
Putting it through a mist nozzle would indeed only cause trouble…
I am not sure how effective straining would be as I assume the oils will hold on to the plant matter.
Unless a watering can works too, I am not sure how to avoid distillation …
Crows and ravens are excellent snail/slug eaters. Even in gardens that are in neighborhoods. That requires keeping cats and dogs out of the garden. And they know you, they remember who you are, and they teach their young who you are (there are studies that show this is the case), so be nice to them, don't shoo them away, don't yell at them, always speak in a nice tone, and they will pass the word along to all of their snail/slug eating pals. If they show up while I'm working, I take a break and let them have what they want.
I make it easy for the ravens/crows, and alerted them to the presence of snails and slugs by going out in the morning, collecting snails in a large yogurt container, then putting that container first not far from where I found them, then on the driveway, away from the garden, but close enough so they get the connection. I find the shells dropped at the bases of the posts they sit on to eat them. Even my neighbor, whose fence is 1/4 mile away from mine has found dozens of snail shells at the base of some of his 4-foot wooden fence posts, he's pretty sure they came from my garden, but maybe from his place, too.
Some years are worse than others, so it's not always the case that slugs and snails will ruin everything.
Copper is another plant protector that snails and slugs can't cross over because they get a shock. Pennies have enough copper on them, and if you glue pennies onto a strip of something flexible that can withstand the sun, like an old, wide electrical cord, or flat polyester rope, you can tie lengths of them around the bases of fruit trees, and lay them flat on the soil around the base of a bushy plant, making sure the pennies touch each other so there's no gaps between them.
They also don't want to cross over lines of coffee grounds, but those disappear with the rain, so they could be used until the copper strips are available.
Don't fall for the My-Place-Is-Special, It-Won't-Happen-Here Syndrome.
Hugo, what phytotherapy book are you talking about? And the pond you dug, does it have any running water to refresh it, or is it just a large stagnant body of water? I have a 5' deep hole in clay I made during some folly thinking "root cellar", but it is already well on its way to ponding. And close enough to my gardens!
and GAH, I HATE RESTRICTIONS ON INFORMATION. Hugo, you might try a VPN. I will post the text of this important article below my post. KNOWLEDGE IS FREEDOM, KNOWLEDGE MAKES WISDOM, KNOWLEDGE MUST FREE. The nematode info in the article is also interesting but of less immediate use to us, who must wait for the Products of Industry.
Sebastian, true, ease of dispersal suggests oils are necessary on any large scale. But before the investment I can try the watering can. Should do it for a few months to see what else, if anything, gets disturbed.
And Cristo, THANK YOU! That is wonderful and useful info. We have plenty of ravens and crows waiting for handouts. My only concern is that attracting their attention may lead to other, tastier things than snails (e.g. my crops) being denuded. I think here and in Oregon, slug plagues are an assumed feature of the future, hence the recent hiring of that slug expert prof and the research.
I use pieces of perforated copper foil I got from a scrapyard to make barriers. After 1975, pennies only have 2.5% copper so I'm glad to hear so little works! I've seen slugs reaching over the barriers trying to grab low branches to pull themselves up by herculean muscular effort. So the width of barriers should take the size of your slugs and low-hanging branches into account. I've also used, with varying levels of success:
-coffee grounds (yes the rain is a problem)
-epsom salts (added benefit of getting magnesium in your soil, but rain washes out)
-diatomaceous earth (also a rain problem)
-ashes (blah blah rain)
-biochar (this in theory should be very effective but trials are ongoing)
Researcher identifies new weapons against slugs By MATEUSZ PERKOWSKI Capital Press Dec 11, 2018
New weapons are being discovered in the battle against slugs.
Essential oils from thyme and spearmint are proving lethal to crop-damaging slugs without the toxicity to humans, animals or the environment that chemical solutions can present.
An added advantage of these oils is the rapid mortality they cause in slugs, whereas one of the most common chemical molluscicides used by Oregon farmers, iron phosphate, simply causes them to stop feeding, said Rory McDonnell, Oregon State University’s slug specialist.
“The oils were essentially just as effective as metaldehyde,” another common molluscicide, McDonnell said during the Oregon Seed League’s annual meeting, held in Salem, Ore., on Dec. 10-11.
Thyme and spearmint oils achieved 100 percent mortality at a concentration of just 0.25 percent, most likely through direct contact with slugs — though it’s possible their volatile emissions could also serve as repellents for the pest, McDonnell said.
Because they’re natural compounds, these oils would be exempt from the U.S. Environmental Protection Agency’s registration and residue tolerance regulations for conventional pesticides, he said.
Before they could be commercialized as biological pesticides, data would need to be submitted to the Oregon Department of Agriculture proving they’re not toxic to humans or non-target organisms, though this should not be a big obstacle, McDonnell said.
“I’ll eat my hat if it’s toxic,” he said.
McDonnell was hired by OSU in 2016 after Oregon farmers told the university’s leaders that more research was needed to fight slugs, which have become increasingly destructive in recent years.
Another positive development from McDonnell’s research is the discovery of a nematode that’s naturally parasitic to grey field slugs — phasmarhabditis hermaphrodita — on OSU’s campus in Corvallis, Ore.
The location if the discovery was ironic given that McDonnell had traveled thousands of miles around the state searching for the species, which is native to Europe and used in slug control there.
“The darn thing was a stone’s throw from my office,” he said.
Since then, McDonnell has discovered two other nematode species in Oregon that show promise as biological control agents.
In the United Kingdom, the phasmarhabditis hermaphrodita nematode is sold as a commercial biopesticide that’s been shown to reduce slug damage in winter wheat by 85 percent, he said.
The nematode finds a hole in the back of a slug’s head, then vomits up a bacterial soup that’s toxic to the gastropod. As the slug’s body decomposes, the nematode’s offspring feed on its corpse.
The BASF chemical company also markets the nematode in Europe, producing it in enormous vats through a secret process, McDonnell said.
Before the nematode can be commercialized in the U.S., BASF or another pesticide manufacturer would need to demonstrate to USDA that it’s not harmful to other species, such as the native banana slug.
“I think that would be a major stumbling block,” he said.
Fredy, I've never had any problems with the crows or ravens going after fruit. The bluejays, the robins, yes. But I plant some sacrificial blackberry vines for them, and that keeps them busy. There is usually a bluejay nest near my garden, and they squawk as they fly to steal berries for their babies, but several plants for them keeps them off the plants I want. In a smaller garden, just use sheer curtains. Bluejays will eat insects, too, so they aren't all bad.
Sheer curtains can be tied over the fruit trees or berry bushes, tied down with a rope through the curtain rod pocket, for the 4 or so weeks of fruit ripening/picking keeps the other bird maurauders away, yet still allows light through the curtains. Curtains last longer than agricultural fabric, and can be bunched up into long bundles to make insulation rolls around plants or greenhouses or seed starting trays when they start falling apart.
Don't fall for the My-Place-Is-Special, It-Won't-Happen-Here Syndrome.
Hmm I must have peppermint then as the slugs EAT IT! A quick google search comes up with 100g of fresh spearmint being needed for 0.20g of oil. so that's 2.5kg for a teaspoon, 11 pounds of fresh spearmint for that gallon of slug killer, (at 2tsp a gallon) I certainly think that's something that would only be worth buying rather than trying to distill oneself.
Fredy information must be free, i like how you think, it should be, it's the fast way forward for humanity!
If the slugs have a 100% mortality rate at 0,25% thyme oil by direct contact that's not a win really is it? So you have to find them first, might as well snip them in two or collect them in a bucket and remove them elsewhere. I've heard they're mostly nocturnal and for every one you see 4 or 5 have dug themselves in the ground or found a place under a rock, it's just the very hungry ones we catch at dawn and the fall of night.
If i make lavender oil, i get maybe 25 ml oil or 50 but i got litres and litres of hydrosol, which could be in theory just as lethal to the slugs. I'll have to try to make some and do my own experiment this spring when i see them coming.
This is not a permaculture method but interesting never the less. Could be done with solar panel and transformer though. Someone else i know had a copper strip tacked on the wood of raised bed, that helped she said.
And for commercial growers it could keep them out of polytunnels, still have to deal with the ones that have dug themselves in the year before inside the poly tunnel.
People have these running ducks as well that eat snails.
They're buggers these slugs, i really hope these huge ones do not return this year that migrated north, they massacred my plants a few years back.
My pond is receiving roof water, i've got an ibc tote that catches a thousand litres and the flow over goes straight into the pond through a pipe , in summer i got the IBC tote to keep the pond at a high level, i scoop water out for the garden as well. The phytotherapy book is called Groot Handboek Geneeskrachtige Planten by dr Geert Verhelst, it's a Belgian, so unless you know dutch of no use.
Creating edible biodiversity and embracing everlasting abundance.
Skandi, it's all in the name: peppermint makes things more tasty, spearmint kills them like a spear in the gut! ;) Definitely going to start with essential oil application before going to distilling. I'm always looking to justify distilling gear.
Cristo, I didn't know that about sheer curtains! Will be helpful for keeping birds out of the autumn olive when it fruits, which is supposedly the only thing you need to do to prevent its becoming opportunistic. Sheer curtains are also more likely to be available secondhand than ag fabric.
Hugo, I'm not thinking of direct application, but of spraying all cultivated areas with a very fine mist (hence the importance of a solid-free liquid). In 10 minutes near sundown, when all the slugs are whetting their knives, you can pass by the beds and put some napalm salad dressing on there for them. Everyone dies or is repelled, very little effort for you. If the repellent effect were very strong, you could even plumb a tank of thyme repellent into your drip watering system...but i'm getting ahead of myself.
That is a great video. I've thought of electrical repellent systems and that lays it all out so neatly. Will add that to the armamentarium, but only with rechargeable 9v batteries or solar panels + transformers if I can find them cheap enough. Unfortunately that system may keep snakes out as well, and so far they are my most effective control.
"Maria Thun makes a let-it-rot slug spray: When moon is in Cancer, collect 50-60 slugs and leave to rot in water. Next month, when moon is again in Cancer, strain liquid and spray on soil, prepare a new spray and repeat next month. Repeat for 3X at intervals of 4 weeks. Hugh Courtney reports using a tea from spruce seeds to discourage slugs. To make the tea, 3 grams of crushed seeds of Picea abies (Norway spruce) were left to ferment in 1 liter of water for two weeks. One cup of the fermented extract was added to 2.5 gallons of water, stirred for 20 minutes and sprayed on the soil and plants with good results. Similarly, Hugh makes a tea from pokeberry (Phytolacca americana) juice. Results are not clear although one Oregon grower reports success using pokeberry juice early in the year to inhibit slug reproduction."
Finally, this biodynamics company says a seaweed preparation repels them, though the purpose of application is to fertilize. I've got seaweed for miles and need to gather it for my asparagus beds anyway.
No matter how many women are assigned to the project, a pregnancy takes nine months. Much longer than this tiny ad: