About six years ago, I was given the opportunity to sit in on a “master class” webinar for Master Gardeners with the topic title “Frontiers in Slug and Snail Management.” It was presented by Oregon State University’s Extension Service and led by Dr. Roy McDonald who is doing all sorts of research on slugs and snails at OSU’s Department of Crop and Soil Science. It was pretty interesting and people from all over the United States took part in the webinar.
We started out by learning the parts of the body of these two gastropods, important when you are trying to identify them. And the only reason this is important is that some slugs and snails are more troublesome and invasive than others. They are pests in agriculture and horticulture, in urban, suburban, and natural areas. But they are especially annoying pests in home gardens. They can be vectors for human pathogens (which are fancy words that mean they can spread diseases to humans). They also can be aesthetic problems to fruit and vegetable growers who count on a lovely product to sell to the public.
Native slugs aren’t generally the problem that European snails and slugs have been. And that makes sense as our native banana slugs eat mostly native plants. European brown garden snails (the ones we see in Tillamook) do the most damage in nurseries and lay their eggs about two inches under the soil surface. Amber snails are also problems in Pacific Northwest nurseries. The gray field slug is the most damaging species in the United States because they attack ornamental plants, fruits and vegetables. They can be identified by the milky-white colored mucus they secrete.
Dr. McDonald reviewed the chemical molluskicides like metaldehyde (Deadline), iron phosphate (Sluggo), and chelated iron (Slug Kill) and discussed their effectiveness in the home garden. Of course, I knew metaldehyde was the most effective, but it is also very toxic to pets. So, if you have pets, the best product to use is the iron phosphate.
Handpicking and traps are alternative methods to using chemicals. Last summer, I purchased 3 traps from TheOregonSlugTrap.com. They come with a hinged lid and stakes on the bottom to secure them to the ground. Available in 5 colors, they were reasonably prices at $4. I tried mine with (cheap) beer and they did pull in the slugs. The only drawback is having to clean dead, slimy slugs out of the traps regularly. But that is the case with any slug trap.
The most important thing in any of these methods is the attractant that is used to draw the slugs to the traps or to the chemicals. Interestingly enough, the scientists are finding new and novel attractants that have been very effective when used as bait. We were all surprised to learn the most effective is fresh cucumber! By chopping up fresh cucumber, apparently the slugs will flock to your traps. Forget about using beer… cukes are the way to go to draw those snails and slugs in and I will be doing that this spring. Since
large-scale nurseries and farms can’t really be cutting up hundreds of cucumbers every day, scientists are working on a chemically-created substitute for using real cucumbers as bait.
The ultimate goal of the scientists is to find effective chemical controls that will work on a wide range of slugs and snails. But showing some success in European studies is the use of nematodes as a biological control.
Nematodes are considered to be natural enemies of slugs and snails as well as other destructive insects. Simply, they are a form of roundworm in the phylum Nematoda. Some are problematic in their own right, but beneficial nematodes can aid as an alternative in insect control. In this case, the variety used in Europe is one that is lethal to a variety of slugs and snails and has been found to protect European crops. It is not currently available in the US, but when it is, our climate in the Pacific Northwest should be optimal for their survival. I have a feeling it will be expensive to use, but then again, what would we pay to be rid of slugs and snails in our gardens? I wager the answer is, “a lot.”
Another biological control finding success in the United Kingdom the predacious ground beetle. In fact, in the UK, studies have shown that when the beetle population increases, slugs and snail populations decrease. The key here is to find which beetle species will feed on the invasive slugs and snails abundant in the United States.
The bottom line is that there is no quick fix and we must start thinking outside the box… or dare I say, “outside the shell?” Integrated Pest Management will be the key. We must learn to use a variety of methods and find the ones that suit us the best.
If I have piqued your interest in slug and snail management, this webinar is now available on YouTube for anyone to watch. Just go to YouTube and type in “Frontiers in Slug and Snail Management” in the search engine and you can take this master class, too.
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