Willow leaves suddenly brown and dropping

This pussy willow was previously 15-20m tall. During the winter we had it pollarded, and this spring and summer it has put on tremendous healthy growth. However, seemingly quite suddenly (literally we didn't notice it last weekend), the colour of the canopy is turning from green to dark green/brown, and leaves are starting to drop. I've included photos of the tree and a close up of the leaves.

Any thoughts on what this might be? Thank you.

 

If you've had a lot of wind and not much rain where you are over the last few weeks, this could be a natural reaction to drought. I've had a couple of trees doing the same in my garden. Provided there's no sign of disease and just browning of leaves, I wouldn't be too concerned as autumn approaches and the leaves fall. You could try extra watering now to keep the roots hydrated but the leaves won't green up or return until next year.

 

Quite often during the summer these get attacked by aphids, they cover the underside's of the leaves, other bugs attack as well.
They start to look tired at this time of the year, especially in dry weather.

I agree with @Plantminded its not going to improve much this year but should be ok again next year.

Got to admit its not one of my favourite trees.

 

Thanks both - this is reassuring!