I've fought pests for years with different things. Slugs like beer. That worked for a while until the neighbors dog learned when to drop by each day.
A trail of salt around the perimeter also worked for a while.
Bacillus (BT) helps also when mixed with dish washing soap if you spray the underside and around the base of plants.
My favorite is the cheapest tobacco and gin steeped together and let set in the hot sun for a few days. Dilute 10:1 with water and spray the entire area.
This works on many pests and good insects too, unfortunately. Don't be tempted to smell this stuff unless you want to empty your stomach. It is very foul.
Dichotomous earth is supposed to work. I haven't tried it though.
Niall, I think the key is to work the soil around the plants to kill as many as possible, then trade off different methods because they will get immune to them over several weeks.
Just my way of staying off pesticides because they work on people too.
Good Luck!