Whether or not the entire tree needs to be removed is something that cannot be answered by the evidence of one picture. I can tell you that its presence means that it is killing the limb OR that there is already considerable deadwood in that limb. If the rest of the tree looks as bad as that limb does...put it out of its misery.

Lilacs are notoriously prone to problems. If this one is a commanding presence in your yard, you should seek the expertise of an ISA (International Society of Arboriculture) certified arborist for an evaluation.

that fungus is decomposing dead wood ...

i doubt it killed it..

cut it as close to the ground as possible .. and see what it does the rest of the year ...

lilac are rejuvenated thru .. get this.. rejuvenation pruning ... a trunk that big.. should have probably been pruned out 10 to 15 years ago ...

odds are.. nothing kills a lilac .. i have seen hundred year old trees in front of centennial farms ..

just remove that part.. and odds are.. it will go gangbusters ...

ken

Thanks- it is a pretty big tree and that is the only limb effected. I will cut it out and keep my fingers crossed.