My educated guess is it is succumbing to a wilt disease - verticillium, fusarium or other type. Infection is almost always through the roots. Wilts are vascular diseases that infect the vascular system in the stems and disrupt the flow of water (and nutrients). Often you will find only certain branches or individual stems affected initially, rather than the entire plant. But the whole shrub may go all at once too.

One of my early lilacs (Syringa x hyacintha(?) 'Asisseppi'(sp?) gets it about every other year. It loses a main branch or two, and then compartmentalizes the disease so it can do no further damage. Syringa x hyacintha 'Lemoine' totally succumb years ago. My Syringa vulgaris 'Krashavitsa Moscvy' has it now, and jury is still out.

There is really nothing you can do about it to directly attack the disease. Do reduce any known stresses for the plant and try to keep it vigorous so it can combat the disease on its own. This is a disease that can be spread by pruning infected branches and then cuting healthy ones, and most wilt diseases have many different host species in several genera.

Rick

Rick

Thanks, I suspected it was probably something that was disrupting the flow of water. Hopefully at least part of it will be saved.

Pauline