Notes from OSU slug chat with Rory McDonnell
A deeper conversation about bread dough as an attractant to keep slugs off of plants.
If you’ve been on social media recently, a new method for controlling slugs has been proposed by OSU. After having read the proposed control methods, I had a few questions about how it works and its effectiveness, so I attended the “Slug Chat” with their specialist on zoom. The link for the recorded chat is here.
First, here is the verbiage from their Facebook page to catch you up to speed: Research from OSU found the most successful attractant for slugs is bread dough. Rory McDonnell, associate professor and Extension gastropod specialist collaborated with scientists from other states on a study that published in a special 2021 issue of “Insects” that focuses on slugs and snails. “We gave them a choice of food and they consistently went for the bread dough,” Mc Donnell said. “They really, really like it. They went bonkers for it. Bread dough outperformed everything.” In one instance, over 18,000 snails were trapped in 48 hours.
How can you apply this research at home? You can make a bread dough using the researcher’s recipe and hand-pick the slugs from the dough or turn it into a slug slurry to attract the slugs who then drown in the liquid.
Let’s make slug slurry!
A bread dough slug trap
You will need:
1 cup flour
2 cups water + more as needed
1 packet yeast
Small container (recycle a yogurt or cottage cheese container, for example)
Mix together the flour, water and packet of yeast. Add more water as needed to make a slurry. (There isn’t an exact measurement because the water will evaporate and fresher yeast may cause the dough to rise in the container. You need it to be in a liquid form to trap the slugs with this method.)
Pour the slurry into a small container.
Dig a shallow hole in the area where slugs may be living in the garden.
Place the container of slurry in the hole, with the edge of the container at or just above ground level. Fill in the dirt around the container.
Check the container every morning and remove slugs. Refresh slurry as needed. Notes: The dough works best when it is moist. Stir daily and add water as needed.
If you prefer to make the dough and not the slurry, reduce the water by half and plop your dough blob in the garden. Be ready to handpick the slugs out daily and keep the dough moist.
Keep dogs away from bread dough in the garden.
My first question regarding this method: does this method actually kill slugs?
The answer: bread dough is an attractant only, and it is up to the gardener to dispatch the slugs. A “slurry” will cause them to drown - though my experience with beer shows that often they do not drown - they drink the beer and move on.
I wasn’t able to get a clearer answer on exactly how bread dough is used to control slugs. I get that bread “dough” or “slurry” is an attractant. But in practice, how exactly does this work? Once the slug is attracted to the dough, does it stay there for the gardener to kill in the morning? I would think not, as slugs tend to hide in dark places during the day. Does this mean that a trap must be made with the dough, that mimics a dark place for slugs to hide so that they’ll stay there? Or is the thinking that the gardener goes out at night to kill the slugs on the bread dough?
And for the slurry - is it actually any more effective at getting slugs to drown than beer? Perhaps I’ll need to set up another experiment to find out.
Second question: would this method actually attract more slugs to the garden?
The answer: bread dough has only a 1 meter draw distance. This is important in particular for gardeners like me, who are growing on a larger scale. Traps are ineffective beyond one meter. A trap will need to be maintained and placed every 3 feet or so. In my mind this is impractical to do on a larger scale, but, it may help in smaller situations where you’re trying to get sensitive seedlings established or perhaps June-bearing strawberries ripening.
Earlier in the season, I chanced some cauliflower and lettuce seedlings and placed them out during a warm spell. They were growing swimmingly until the weather turned super rainy for about a week. Then the slugs came out and devoured quite a few of them. This might have been a situation where I could have used the dough method with some success.
Other notes I wrote down:
Bread dough is poisonous to dogs, cats, and presumably wildlife.
A note on baits: their effectiveness is quite poor. When they work well (and they often don’t) you can only expect up to 60% efficacy - often lower. This explains to me why some folks often have success with baits - they must have lower slug populations than I do.
Side note: there is a whole page on baits and their effectiveness. Did you know:
-Some species of slugs are resistant to baits.
-If slug populations are high, baits are unlikely to reduce levels to avoid damage on plants.
-Baits can lose their effectiveness in as little as half a day.
-Baits are best applied between 50-70 degrees (soil temp 63 degrees), light rain (not heavy rain), very little wind, applied September/October or Feb-May.
-Nightcrawlers will pull the baits underground where slugs don’t reach them.
-Slugs can recover from bait poisoning, and will avoid baits in the future.
-Heavy rains will dilute the bait, reducing efficacy.
Slugs are implicated in the spread of e-coli on greens, among other pathogens.
Essential oils are another area of research being conducted. Evidently thyme and spearmint oil are toxic to slugs. They’re still working out how this would work as a pesticide, and what concentration the formulation would need to be in order to avoid phytotoxic effects. However, one useful way that this method has been employed is by mixing OTC essential oils with Vaseline, and spreading a layer around table legs to keep slugs from crawling up onto a table of seedlings.
Nematodes are being studied as well. This is currently not allowed in the US, as they still don’t know what the effects would be toward other insects.
Copper: has worked in some situations. It has been most effective in citrus groves in California, by wrapping the trees with copper tape. Often does not work in our climate, especially once the copper oxidizes.
OSU maintains a slug portal with more information. But I do note that some of the info on the website conflicts with what I learned in the slug talk.
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