For slugs (A) let the girls out there, they will clear your land of bugs (B) get a pump pressure bottle, add 1 tbls of organic soap (guess it can be dawn or something), go out and mist your plants and soil at dusk AND dawn for a few days and they will be gone. (C) Buy cheap beer for the slugs, drop a catfood type can in the soil, fill with beer, it will draw the slugs in and drown. (D) place a copper either wire (anything as long as its atleast 1-2 inches out of the soil) or flashing believe it or not, the claim is that it will conduct energy and shock the little buggers.
As for a Japanese beetle issue, do not place those beetle traps near your garden. Go hang it under your mail box at the end of your drive, then the beetles will go there and not drawn to the plants.
Potato bugs I use Rotenone (sp) its "organic" very posionous tho. What you do with that, is you can mix it in water to keep the dust down, or, use in a duster, Ive used it both ways. It is made from the tuber of a lilly in the rain forrest (I think) and as you put it on your plants, make sure you do this at dusk to be able to work over night. See , once the toxins are met by UVA rays of the sunlight, it nutralizes the chemical that harms instects. This will also work with slugs. So don't bother using it in the day, wash your food and like I say, it kills a lot of bugs, but most of the helpful ones like the bumble bee, honey bee's etc, it will not create issues for them.
Interestingly, rotonone may be coming off the market for the simple reason of government costs of "safety" and a USDA stamp. This has been said for many years, I personally do not know any more then that. It was found helpful when fish ponds needed to be emptied (no idea why) and you use rotonone and by morning the fish would be belly up and clean out was easy. Then with the sunlight, the water was "fine" and they would restock it with fish.
sorry for the over load with info, I almost know what I'm talking about, lol.