I have had really good luck using a pump sprayer and a mixture of ammonia and water, mix with a ratio around 1 to 12, or 1 to 8. I has not harmed my plants (I read it actually is suppose to add a small amount of nitrogen). It seems to just melt the slugs away. I like to spray the plants really well and the ground at the base of the plants also to kill the slug eggs.
It would be a good idea to mix up a batch and just try it on a single plant, make sure you have the mixture strong enough to instantly kill any slugs it contacts, but not strong enough to harm the plant. When you feel safe with your mixture then spray all of the plants and the area they are in.
I had lots of snails and slugs in the early spring and I used this mixture first on my hostas to control the pests, then when I saw how well it worked on the hostas I noticed the daylilies were becoming slug food, so I started using it on them. I would go out in the early mornings or late afternoons, or right after a rain, anytime I thought the slugs were active and crawling around on the plants. Then I would spray any snails or slugs and watch them melt away.
After the early spring wet weather was over I had less and less slugs and have not sprayed for them at all for several months now.
