The scapes have corky lesions. Use rotenone or Sevin.
Mites cause the leaves to turn yellow and have a dusty appearance.
Heavy infestations form fine webbing. Applications of rotenone control the pest. Slugs leave a slime trail which looks like part of the leaf was varnished. Use baits containing Mesurol or metaldehyde. Japanese beetle can be controlled with sprays of methoxychlor, Sevin, or rotenone.