Our California lilac have large parts of dead leaves on them. Is this winter kill or disease. Should we prune them back,pull them out or wait until next spring
Lilacs are very hardy, so it won't be winter kill, likely a disease. Check out Pseudomonas syringae, to which they are susceptible.
Maybe wait before pruning and see if it sprouts new growth within a month or two. This evergreen Ceanothus (California Lilac) is not as hardy as the deciduous Syringae type and it may be frostbitten. The Ceanothus thyrsiflorus 'Victoria' was hit hard at at least one local nursery retailer in Burnaby this past winter and it's one of the hardier Ceanothus varieties. It's not unusual for it to get frostbitten during cold winters on the mainland and Vancouver Island. I'm not sure if it would be considered a true lilac Michael, but it's commonly called a California lilac around here ?
Cut off clearly dead parts, leave any that looks like it may come back later. 'Victoria' may be a re-naming of 'Skylark', which is thought to be from C. thyrsiflorus var. thyrsiflorus x C. velutinus, and not a pure form of C. thyrsiflorus. See p. 98, David Fross, Dieter Wilken, Ceanothus (2006, Timber Press, Portland).
