First of all, what exactly is a slug anyway? It is a Mollusk. It is, basically, a snail without a shell to call its own.
Next question- why do we care about slugs? Because the little rascals feed on our hosta leaves with their file- like tongues which they use to gouge out plant tissue. They do not kill hostas, they just make them look bad.
Not a hosta lover on the face of the earth has not concerned themselves with controlling slugs at one point or another. Having tried virtually every slug control method known to man over the last fifteen years or so, I can say with certainty that most work- at least a little bit.
You can go out after dark and hand pick them and dump them in soapy water. Trust me, they will breed faster than you can pick. You can set out beer traps for them. Not fun cleaning out the traps which should be done daily.
You can try diatomaceous earth spread around each hosta. That works well until it rains. Finally,you can resort to chemical warfare, which is what I have done.
I use a product called Deadline which is a very hard little turquoise pellet which contains yeast (to attract the slugs) and Metaldehyde which causes them to stop feeding and kills them. Deadline contains 4% Metaldehyde.
It is considered toxic but I have found that the pellets seem to be ignored by everything but the slugs- even by my black Lab who generally will eat everything that won’t eat him first. It is applied by simply broadcasting in the beds when the hostas are first beginning to emerge in the spring.
The pellets are hard enough to resist rain and watering for a few weeks. It is important that the first application of Deadline be timely because it is hard to control slugs with anything short of a nuclear bomb once they have begun to breed.
In my garden, I lay down the first treatment when the hosta pips are up but not yet unfurled. That usually means late April or very early May here in the Midwest.
Under optimal conditions, a single slug may produce as many as 800 offspring in a single season. Yes, that’s right; I said single slug since each individual has both male and female reproductive organs. I put down another application of Deadline in late June and the two applications per year control the slugs very nicely for me.
You notice, I said controls them, not eliminates them. Deadline is sold in 10 lb. and 50 lb. bags and is generally sold at agricultural co-ops like Farm Service. I know that the Co-op Conserv carries it and has locations both north and south in the Chicago metro area.
There are other products which use iron phosphate to control slugs. It appears that those products are effective. My problem is that they cost so much by the pound that I find them unrealistic for me with my one and one half acre property. The brand names of the iron phosphate products are Sluggo and Escar-go.
The timing of garden clean up can help keep slug populations down. Slugs overwinter in garden debris but most that survive our winters here in Northern Illinois do so in the form of eggs. Cleaning up the garden in late winter or early spring will expose some of the egg clusters to the elements.
Keep the damage which slugs do to our plants in perspective; they deface them but they do not kill them. Usually by the time you see lots of damage to your plant’s leaves, it is too late to effectively treat them. Well… there is always next year.