Curling leaves on new weeping cherry tree

Hi,

Planted a new white weeping cherry tree about 5/6 weeks ago.

Up until a few days ago, looked quite vibrant, loads of cherrys on branches.

Now noticed all cherrys gone (which I guess could be birds) but more so the leaves are still green, but curled & brittle.

Has the recent very dry & then days of severe rain perhaps caused this? On closer inspection there are some leaves with holes in, but that's in minority. I've read that on an immature tree this could be caused by over watering? Soil still looks moist so will avoid watering next few days. Just wondering whether this is the start of a disease?

I have been watering a couple of days a week since planting 5 weeks ago. No leaves have turned brown yet

 

Cherry blackfly? Look on the curled up leaves on the underside.

 

No sign of cherry blackfly under any leaves. Just curled, very dry/ brittle leaves. Not sure whether it needs more water or less?!