It is summer, sort of. Keep in mind many willows are northern trees that can have only a few months of growth followed by 6 months or more of dormancy. Your tree probably leafed out in March, had leaves for 6 months now, and the oldest leaves are falling. Probably pretty typical. check for aphids, if you don't find aphids on the small twigs, then you probably just have a willow that thinks frost is next month. My pussy willow is already naked, this gives more light for the plants that still know it is summer.

It is much too early for even willows to be losing leaves in preparation for winter dormancy. It is much more likely that it is suffering from one of many fungal issues that can plague the genus. Check out "willow blight", a kind of catch-all term for an assortment of these issues, most of which are rather treatable. And with willows, there is always the option of coppicing or hard pruning, which can remove the infected tissue.

Willows are simply a genus that is prone to a whole host of disease and insect problems, not to mention having weak wood and an extremely aggressive root system.

Considering that Willow Blight occurs more in the middle of the season and affects the young leaves (not the oldest ones as pictured), it almost surely isn't that. Also, Willow Blight leaves the twigs blackened and there is no evidence of that nor does the OP say anything about discoloration of the wood.

Cutting a branch might show signs of a pathogen, but I still maintain that a cross section of the wood would reveal nothing.
Willows are indeed short lived, weak wooded trees. They are subject to a host of insect, fungal, bacterial and viral problems. They are usually grown for a few years and replaced, coppiced, hard pruned or whatever you call it. You can make new trees by rooting a branch in the spring. Easily done, then you can cut the old one down and start over.

Your tree looks too young to need replacing. Enjoy it for why you planted it, accept that usually some of the leaves will fall early. I doubt it harms the tree, and treating phantom diseases will not help.

based on your lawn.. i see drought

i am 6 weeks into a drought..

ALL OF MY TREES ARE SHEDDING LEAVES.... or have really ugly leaves....

unlike gal.. we do not live in the PNW ....

only someone with a ridiculous amount of money to waste.. starts spraying trees with 'cures' ... weeks before the leaves fall off ... all cure are topical.. so whats the point.. eh????

all that said... one of the most horrible yard trees in the world for a backyard ...... i sold my last house.. and moved 65 miles to get away from them ...

gorgeous park or golf course trees.. where someone else is responsible for them...

kill it and plant some heritage trees.. and you will be making a better life for yourself..

and for a nickle.. i will tell you how i really feel about them ...

REDRUM!!!!
ken

Good morning, thank you for all of the replies I have received regarding this. I do believe the willow went to leaf early this year so we will just keep it watered and see how it does next year which was kind of my thoughts on this.

In regards to ken's comment on the willow tree being a horrible back yard tree I do believe everyone is entitled to their own opinion and their own taste. Thankfully I do love the willow tree which is exactly why I planted it. Growing up when I would visit my grandparents they had this, and still do have it by the way after 40 or more years, giant willow tree in their back yard that was so beautiful.

So you may have your own trees of your choice in your yard while I have mine and I will respect your opinion on the matter.