Q.My lilac tree hasn’t flowered and the leaves have curled and gone brown, but it has buds on. I’ve taken the curled leaves off.
Could you please suggest how to save my lilac tree? I’ve looked for pests but there is no sign – just leaves curled up & brown.

Certified GKH Gardening Expert
If the area has been overly wet, or have been manually watered too frequently then this could be a severe fungal infection. It can be difficult to pin, exactly, what it is without seeing it but this is most common.
Fixing it will require a fungicide, and some soil preparation.
This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
I would also treat the soil around with about 1/2 a cup of DOLOMITIC LIME and a full tablespoon WETTABLE SULFUR.
This, cast evenly around the soil near the roots, will help clear out the infection in the soil, as well as condition the roots from the treatment.
This article will offer more information on the care of Lilac: https://www.gardeningknowhow.com/ornamental/shrubs/lilac/lilac-care-growing-and-planting-lilac-bush-plants.htm
This article will offer information on getting one to flower, should these treatments not correct the flowering portion of the issue: https://www.gardeningknowhow.com/ornamental/shrubs/lilac/lilac-bush-not-blooming.htm