About diatomaceous earth and slugs

Someone suggested that I could use diatomaceous earth to get rid of slugs in the garden. Is this a good idea? Any drawbacks I should consider?

First, here is a definition of what diatomaceous earth is, from the National Pesticide Information Center: “Diatomaceous earth is made from the remains of diatoms, which are tiny organisms that lived in rivers, streams, lakes and oceans. Diatom skeletons are made up of silicon dioxide, a combination of silica and oxygen. Silica is very common in nature and it makes up 26% of the earth’s crust. Diatomaceous earth is very abrasive to an insect’s exoskeleton, causing them to dry out and die.”

Slugs are not killed by diatomaceous earth, though it may slow them down. It is mainly used to control insects with hard exoskeletons. According to the book Mason Bee Revolution (Dave Hunter and Jill Lightner, Skipstone Press, 2016), the abrasive dust can damage the bodies of butterflies, spiders, and some bees by causing severe dehydration; it can also kill beneficial hard-shelled bugs. It is considered a relatively low toxicity method of pest control, usually sold as a dust. However, it is not entirely risk-free: wearing a respirator is recommended. Prolonged exposure can cause serious problems like silicosis).

Using submerged saucers of beer will take care of slugs without adverse consequences for non-target species. A potential alternative slug and snail control method that has yet to be researched thoroughly is using wool as a compost or in pelletized form. Excerpt: “Wool may also be included in mulch or mats where it has been shown to reduce predation by slugs and snails, eliminate weed growth, and reduce soil temperature variation.”

Pesticide safety measures, Pests, Slugs, Snails

growing artichokes

I have about 20 healthy artichokes. They did not die back in the winter. I think that there is a lot of bug activity going on in them: earwigs, slugs. Should I cut the plants to the ground and dispose of the possible bugs that have wintered over in them? I hate to do it because the foliage is so lovely.

I have grown artichokes for the last 5 years, so I am going to answer from personal experience.

Do not cut the plants back because they will be sending up their flowers in the next few weeks (depending on the weather, it could be as late as June). Cutting it back now will just delay any flowers for at least 6-8 months, if not kill them outright. While I too have had numerous slugs, earwigs and cutworms, I find that their damage is minimal, and does not hurt the flower show. And for eating I just wash them carefully and then turn a blind eye when I find a few earwigs in the pot after cooking!

Sprinkling some Sluggo (or comparable less toxic slug bait) into the leaf joints will help too.

controlling slug and snail damage on cannas

My canna has a leaf with a set of 9 holes in a straight row, all symmetrical with each hole a bit bigger than the one to its right. Any idea what’s causing this? I must say that we’ve been greatly amused with our yard this summer–it seems like every day there’s some new critter or discovery.

I found the following information in The Gardener’s Guide to Growing Cannas by Ian Cooke (Timber Press, 2001):
“Cannas seem to be particularly attractive to slugs and snails and can be totally devastated by them. Unless you control them, expect young leaves to unfurl with cut patterns like a child’s paper-tearing exercise!” (This is a Britishism for what we think of as papercutting, like paper snowflakes.)

The easiest approach to slug and snail control is to use the newer generation (organic garden-acceptable, but not good to use where runoff will enter lakes and streams) slug baits which are wheat gluten-based pellets with iron phosphate as an active ingredient (such as SlugGo and EscarGo). Be aware, however, that there are reports of dogs eating the bait and developing iron toxicosis.

The safest approach is to use the following non-chemical controls (traps, barriers, natural predators):

Northwest Coalition for Alternatives to Pesticides, click on link to read document.

on the use of iron phosphate based slug baits

Is there any scientific reason to not use the iron phosphate based slug baits (Sluggo etc.) near bodies of water (streams, ponds, lakes)? I did some preliminary (not exhaustive) Google research and did not find anything to suggest they cause increased algae growth. Please let me know what you can find on this subject. Are other
water-borne organisms harmed?

The Material Safety Data Sheet for Sluggo indicates that one should avoid
disposal of this product near bodies of water (see Section 13), though
there is not definitive information in Section 12 on the ecological
impacts of the product on algae and other life forms. Here is a link to the PDF document.

See also Grow Smart from King County Hazardous Waste Management on dealing with slugs in gardens.

It does not list Sluggo, Escar-go, or any of the other iron phosphate
products as water pollution hazards, but the MSDS sheet makes me think
there is a potential problem with dumping large quantities. It seems not
enough information is out there, perhaps because the research has not
been done. Here is the page from the Pesticide Action Network database, where you can see that iron phosphate’s eco-toxicity has not been
established.

Here is what the Environmental Protection Agency has to say about iron
phosphate slug baits:

Ecological Effects Hazard Assessment

“A number of ecological effects toxicology data requirements were waived
based on the known lack of toxicity of iron phosphate to birds, fish and
non-target insects, its low solubility in water, conversion to less
soluble form in the environment (soil), and its use pattern (soil
application). An acute oral toxicity study in Bobwhite quail (NOEL & LD50
greater than 2000 mg/kg) indicated that iron phosphate was practically
nontoxic to avian species. Based on these factors, the data requirements
for the toxicity studies in Mallard duck, rainbow trout, freshwater
invertebrates, and non-target insect/honeybees are waived. It is likely
that there will be exposure to ground-feeding non-target insects and
earthworms. Submitted studies involving ground beetles, rove beetles and
earthworms demonstrated that the product will not affect these organisms
at up to two times the maximum application rate.

Environmental Fate and Ground Water Data

Exposure assessments on this type of product (biochemical pesticide) are
not performed unless human health or ecological effects issues arise in
the toxicity studies for either of these disciplines. Since no endpoints
of concern were identified, there is no requirement for environmental
fate data.

Ecological Exposure and Risk Characterization

Exposure to daphnids and other aquatic invertebrates would not occur
based on current label use directions. Exposure to honeybees is also not
expected to occur, due to the composition and particle size of the
end-use product and its use pattern (soil application). Non-target
insects, such as ground beetles and earthworms, could encounter the
end-use product; however, in tests of rove beetles, ground beetles and
earthworms, no effects were observed at up to twice the maximum
application rate. Thus, the acute risk to aquatic invertebrates,
non-target insects, and earthworms is considered minimal to nonexistent.”

United Nations Environment Programme has information on the impact of Phosphorus on aquatic life, a process called eutrophication. However, the iron phosphate in Sluggo and similar products binds with Phosphorus, which may mitigate the effects in water.

Garden Tip #72

What unites gardeners from all walks of life? A passionate loathing of slugs and snails. Perhaps if we understood these little slimy mollusks better – their lifecycle, their tastes – we\’d learn to appreciate them for the successful creatures they are. Or at least we could learn how to drive them out of our gardens with the latest science has to offer.
The BBC’s Science and Nature web site once had an in-depth article on snails and slugs that made fascinating reading. https://www.bbc.co.uk/nature/animals/features/291feature1.shtml

This interview with malacologist Mary Seddon may be interesting: https://www.bbc.co.uk/programmes/b01ntj9z

Slugs have memory and will return another night to finish off tasty seedlings until they are all gone.
A few plants slugs find distasteful: foxgloves, many species in the daisy family, Lavateras, hollyhocks, azaleas, Euphorbia, hardy Geraniums.

A long list of “Slug Resistant Plants” is given in a Seattle Times article by local writer Valerie Easton.

Garden Tip #42

A trip through the garden at night with a flashlight will reveal a surprising amount of animal and insect activity. Earthworms crawl across the ground looking for decomposing plants to consume while weevils, slugs and cutworms feed on our prized shrubs and perennials. Remember that the new non-toxic iron phosphate slug baits, such as Sluggo, must be reapplied about every two weeks. More slug-coping advice can be found online at www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7427.html

The Secret World of Slugs and Snails

Secret world of slugs cover David George Gordon wrote a delightful booklet (48 pages) in 1994 titled Field Guide to the Slug. After chuckling over the concept, I found there was a lot of information packed in those few pages.

The Secret World of Slugs and Snails greatly expands the earlier work by not only including snails, but also the natural and cultural histories–yes, including cooking suggestions and even shell collecting–of these incredible creatures. For the even more adventurous, there is a short essay on keeping slugs as pets. For example, banana slugs have a good temperament for this (the author has a pair named Chiquita and Dole) but they will overheat in the typical household.

The final chapter is where most gardeners might begin: “Sharing Our Gardens: Coexisting with Slugs and Snails” but unlike in most gardening books, slugs and snails are not portrayed as an indisputable enemy. Yes, there are suggestions on how to both discourage and eliminate them, but the gardener is urged to have a heart and not apply salt as “…salting causes undue pain for the slug.”

Excerpted from the Fall 2011 Arboretum Bulletin.