Ursula, slugs often move along old slime trails, so if they start to attack one particular plant, they often come back night after night to it, while others nearby can be completely unharmed.
I'd try to water in the morning. If you water in the afternoon the extra moisture will attract slugs during the night. They can follow that moisture up to your lilies. Also check under your styrofoam boxes during the day as slugs love to hide in damp dark places during the day. They often attach themselves to the underside of things, so simply lifting the box may not be enough. Make sure to really look from all angels.
You can also make a beer trap from a plastic bottle:
http://www.slugoff.co.uk/killi... The slug can't escape such a trap, so it can easily be emptied during the day. Worked very well for me, but the downside is that the smell horrible after a few days and they fill up very quickly. Also one needs to be aware that slugs may appear to be dead, but sometimes they are just drunk...
If you don't have an army of slugs, these small precautions may very well be enough, but there is no doubt that slug bait is the easiest method. I haven't tried baits with spinosad content as in Sluggo Plus as I'm only interested in controlling slugs, however for plain iron phosphate bait I highly recommend using it in a plastic container instead of sprinkling it on the ground as I have found this to work just as good. Sorry, this is in Swedish, but if you follow the link you can get an idea how it can look:
http://www.snigelshopen.se/sni...
Easy to make a similar one yourself! I always place a few containers close to the compost heaps as these otherwise are breeding ground for slugs.The advantage is that the slug pellets will last longer than if put on the ground and if you put a stone on top of the container it will prevent most animals and birds from accidentally eating the pellets. There are some controversy around if some of the additives in iron phosphate based slug bait make it poisonous to other things than snails and slugs, so this is a good precaution in my mind.This is not in reference to the spinosad content in Sluggo Plus, rather there are other additives present to make the iron phosphate work.
