The RHS has some great information and photos of Stagonospora curtisii in Narcissus. The site can be reached at:
http://apps.rhs.org.uk/advicesearch/profile.aspx?PID=735
Worth reading as the fungus can easily be confused with freeze damage.
I DO pick off the tips of any leaf showing signs and dispose of them in a sealed sandwich type bag. Removal prevents the fruiting bodies from forming and re-infecting the ground and plant in further seasons. I agree with Donna’s advice given her by Sir Frank Harrison.
In the USA, Cleary’s 3336 & A. G. Bayer’s Chipco 26019 are recommended fungicides. I also add 1/2 tsp of Physan 20 or one of its less expensive analogs in lieu of a surfactant or sticker spreader.
Steve