Hi, I live in Barrie and this lilac tree is in part sun, sandy soil conditions. It was fine for a few years but last year it looked like it was starting to die. Top part of trunk looks dead but bottom looks ok. Lots of what I believe are suckers. Looks like only one branch blooming on whole tree. Does this tree need to go? Disease? Please see pics
Lilac trees (shrubs) require regular pruning to keep them healthy and to promote the growth that will produce flowers; pruning will help to create a good framework that will allow light to encourage blooms on the branches. It is clear that your lilac is in need of some judicious pruning; the dead and crossed branches will need to be removed.
Lilacs grow best in full sun–at least 6 hours/day. They also require well-drained, humus-enriched soil with adequate moisture. The addition of a layer of organic material–compost or shredded leaves applied in the spring and/or the fall–would not only help to hold the moisture in your sandy soil conditions, but would also nourish the soil.
It’s possible that your lilac can be rejuvenated; first remove all the dead branches; if any branches have new growth showing, cut back to the new growth. On the branch with blooms, remove the spent blooms, cut back to new growth so that it’s proportional to the remaining shrub. Lilacs do sucker; allow two or three suckers to grow and cut back the rest; the suckers will grow into new stems. For more information on rejuvenating a lilac, see here.
Once you have pruned your lilac to remove the dead branches, cut back remaining branches to new growth and encouraged a few suckers to grow, your lilac should eventually form a healthy and well-shaped shrub. To maintain the lilac and encourage flowering in subsequent years, you will need to remove the spent flowers and cut back the flowering stem to leaf growth. This must be done after blooming; next season’s flowers will form on the summer growth.
If the available sun for your lilac is being reduced due to the growth of other shrubs or trees blocking the sun, you then should consider removing your lilac. However, judging from your attached picture, it seems that your lilac simply needs attention; if you prune as suggested, your lilac should revive and produce blooms next spring.