Populous tremula 'erecta' - ant problem?

ki_buxt

Purchased and planted this tree in 2017. It has now grown to a height of about 5 metres. Problem: the last three years some of the leaves have suddenly turned black and the ends of som of the branches have wilted. Almost looks burnt. Haven't seen any pests except ants - they are constantly there, running up the trunk. Could the ants be causing the problem, and if so, any advice? Would using ant powder near the trunk of the tree damage the tree at all?

Also wondering if we can prevent the tree from growing much higher. Would we just need to prune it each year to hold growth back? 

Butterfly66

A close up of some of the leaves might help with a diagnosis. Ants don’t usually cause any damage, they may be farming aphids or going after another food source.

ki_buxt

I looked through hundreds of garden pics but unfortunately can't find one from last year. Seem to remember it happened in late June, so I will keep an eye out and post pics if/when it starts again. 

ki_buxt

Finally found this picture from late June 2019.

Borderline

From your descriptions and what Butterfly66 has said sounded right. However, your latest photo looks like leaf miner damage to me. Not an expert with this but don't think they will be a major issue with the tree or ants.

You can prune the tree in for a light shape, but any heavier pruning is not advisable until late summer and to be honest, they want to get tall, and constant pruning every year to keep at a height may spoil the growth and shape. I suspect that as the tree ages, the growth will be faster each year. I would look into possibly moving it to somewhere further away from your house so it can have its full potential.

ki_buxt

Thanks for the help and advice. Much appreciated.