Annual problem with diseased lilac July to August

What are those white flecks I can see on the leaves?

There are various diseases and viruses that affect lilacs. In our village most of the lilacs have had to be cut down and removed due to a blight which damages the tree. Given the way they sucker they tend to reappear a few years later.

The flecks are in fact rain drops. In past years I have cut off the tops of the branches but this doesn't stop the problem reappearing the next year - the horrible brown patches reappear almost to the same day. I can take more photos, there are leaf falls every day or so. No sign of insect attack. Thanks for your replies.

Could be bacterial or fungal leaf spot, or lilac leaf miner (though with this, you'd see rolled up leaves). The first two can be a sign that the plant isn't healthy - sometimes having too dry or too wet soil conditions can make it more susceptible, or even too much sun or too much wind. Otherwise, I've no idea what it is - might be worth trying a combined fungicide/pesticide spray such as Roseclear 3, and make sure you feed it in the spring with growmore or similar, and again in June, keep it watered in dry spells if necessary, but otherwise, as the plant itself is still growing, I'd just remove any growth that gets attacked in this way. I did once plant a small lilac in a garden which did a similar thing, but to the extent that it grew very stunted - gave up and got rid of it by the third year, when it was still only 2 feet high.

Thanks for your suggestion - strange thing is it flowers in abundance (white) but is in a very sandy soil and does tend to catch the wind over the top of the fence, so maybe not ideal positioning. I shall feed it up next year! Thanks again for your help.