I was told that Banana slugs will not harm plants.
Some people do not like using coffee & tea grounds, but they stopped the slugs eating my basil over night.

I don't put much faith in copper. Search youtube with the keywords "slug copper" and you'll see what I mean.

Diatomaceous earth doesn't work once it gets wet.

How long did you use the traps for? Where were they located? Bowls or pie plates of sugar water, a yeast/bran mixture or beer are very effective. You need to have a lot of them because slugs don't travel very far, and also check underneath the bowls regularly for extra slugs.

You don't have to go outside at night to handpick. You'll find slugs taking shelter under your beer/sugar water traps in the morning, and attached to boards, upturned pots or anything else you leave laying flat on your garden soil. I think they're actually easier to find that way than at night when they're actively feeding on plants. A combination of the drowning and handpicking from boards (or whatever) that you lay out is cheap and effective.

Unbrewed coffee grounds are supposed to work. Used grounds won't -- it's the caffeine content that helps deter slugs.

Also, beans aren't going to grow happily if you've got happy pea seedlings. Peas like cool weather, max 85 degrees. Beans aren't happy in temperatures under 75 or so. Plants grown in suboptimal conditions are always going to have trouble dealing with normal pest pressures. I think your beans' real problem is this, not the slugs (which are probably leopard slugs, not banana slugs?) If they're happy with their growing conditions, they can outgrow all but the heaviest pest pressures.

The copper looks nice, anyway. More ornamental than pie plates and boards.

Here is a link that might be useful: slug on copper on youtube.

I've got really good slug control. It's called "quack, quack, quack". Unfortunately, it also eats the baby green bean plants.

copper's working for me, so far anyway, in another location.

the beer traps were small dishes inset so the edges were level with the soil. left out for a week+. perhaps i should try a different beer or add some yeast.

the beans are (mostly) scarlet runners. they're said to produce in cool climates, but they're planted mostly for appearances. if we get some beans, great. the others are favas.

i'd love to have ducks. no room for a proper pond... and: dogs.

"Unbrewed coffee grounds are supposed to work. Used grounds won't -- it's the caffeine content that helps deter slugs. "
This was interesting enough that I researched the claim. While it seems to be true, there is also a warning that the caffeine may damage foliage:
http://news.bbc.co.uk/2/hi/science/nature/2067214.stm

well, the morning came and there was no new damage.

but apparently my failure with the beer traps was due to not putting fresh beer in them regularly...

Here is a link to an abstract of an article that says, as mentioned above, that caffeine kills or repels slugs. Pest Control: Caffeine as a repellent for slugs and snails.

I wonder if I take the leftover coffee in my pot, put it in a spray bottle and periodically spray my plants, it will kill the snails.

I've done enough hand-picking that all the big ones are gone, but now I'm left with tiny slugs the size of a grain of rice (yet they can still do plenty of damage!).

Anyone tried the coffee solution?

I don't know if they would work in your region, but I found that the use of carnivorous snails ("decollete"?) was a very effective way of managing our snail population.

They will, however, gorge on dog and cat food and become grotesquely huge -- the size of a man's finger, or more -- really revolting. But they do keep the destructive snail population at bay.

I let loose a bunch of 'em 15 years ago, and no more snails. Ever.

(But BLEHHHHHCCCHHHHHHHHHH!)

Decollate snails are only legal in certain California counties (San joaquin and parts of S. California, I think? I just know I can't have them in Sacramento.)

Iron phosphate works.

stopped using sluggo (iron phosphate) due to issues covered in this article (link).

its more work, but the copper, de, removal of slug/snail friendly habitat directly adjacent rows/beds, etc, is working out. also planting some cover/bait crops now so when the cool foggy months hit and the slugs return in force, as they will, there's something else for them to munch on.

whoops, here's that link

Here is a link that might be useful: iron phosphate warning

loribee spray bottle of leftover coffee sounds like a good idea, i 'm going to try it,