Hello Marilyn

I don’t recognize that substance. 
Can you attach a close up( within 2 feet or so) picture of  branch with 5 -10 leaves attached? A couple  leaves  two face up, and two face down on a plain piece of paper may show us something as well.

What other trees are near by? Any maples or crabapples? There could be a pest on another tree that is dropping this, and it is carried onto your patio by the breeze.

I will watch for your pictures.



Thank you for the pictures. This appears to be aphid damage. One possible aphid is the Hamamelistes spinosus, a spiny witch-hazel gall aphid. When feeding on the birch, they leave behind sticky honeydew and white cast off skins.The recommendation from Ohio State Extension is

“Frequently, numerous predators will destroy aphid populations on the birch leaves. However, if heavy infestations on birch are consistently occurring on highly visible landscape plants or in nurseries, aphid populations can be reduced using systemic insecticides such as a fall soil drench application of imidacloprid (e.g. Merit or Bayer are example brands), or a spring soil drench application of dinotefuran (e.g. Safari is one brand)”

The whole article about this aphid is here- https://bygl.osu.edu/node/719

If you decide to use chemical treatment, you can reduce the impact to bees and other pollinators by waiting until the birch tree flowers have dropped and/or begun to form seed. Please follow all directions and precautions carefully when using garden chemicals.

To confirm the diagnosis you may submit your pictures to MSU Plant Diagnostic lab ( email them to <personal data hidden>)

Or, you can hire a certified arborist to come out and diagnose the tree and give you a health care plan. Find certified arborists by zip code here – http://www.treesaregood.org