Silver Birch

I find that you get this from a lot if not all trees. It's part of nature like bird muck. Enjoy your tree and if able just give the car a quick rinse a little more often. It doesn't need a complete soapy wash to get it off.

Birch trees produce an edible sap. What with that and pollen from the catkins (flowers), anything that blows off it will be sticky. This is true of lots of trees. If you can't park your car anywhere else, I'm afraid you're stuck with it.

It's caused by aphids my (tree expert) husband says. We also have a Silver Birch that sits close to our carport and last year he cut it down and it is now regenerating. They are beautiful trees and host a wide variety of invertebrates and lichens.

It may be an aphid infestation. They eat the leaves and secrete 'honeydew', Especially during hot dry years.
Try either a soap spray (which would be hard on a large tree) or perhaps finding some ladybugs, which will eat the aphids.

Oh well....I'll put up with it, it's much too beautiful to cut down and I was only joking.
I'll just hose it off every day.
Thanks all....

We have one at the end of the drive too, and another in the back garden, nuisances, but very lovely.
The sap rains down , and at the moment the catkins are everywhere underfoot too.We have only just finished picking up all the hundreds of twiggy bits that come off every year.Grrrrr.

I will look into finding some Ladybirds.
I have lots in the front garden, in fact they over-Winter on my blinds in the bedroom and as soon as they think it's the right temperature in Spring, start moving about and I open the window and off the go.

It's not aphids - in spring the sap rises, and drips out of the branches. I have a Jacquemontii birch in my garden, and while weeding beneath it last week, got thoroughly dripped on!
I had it cut back in March last year, and the cut branches poured out sap for weeks.