Allium fly

I lost all my leeks last year to allium fly. They laid eggs, which grew into grubs which tunnelled right into the plants, which then rotted. I was told that this pest is not widespread yet, but am certain of the identification as I studdied the grubs with great care.  I decided to try again this year, and keep a sharp eye out at the times they are active. Up to now, late July, I have kept it under control by pulling off and disposing of any affected leaves at the first sign of damage. I also sprayed with a horticultural soap from The Organic Gardening Catalogue. However, a full scale attack appears to be in progress. Is there anyone out there with any suggestions, please?