River Birch Tree disease/insects
My River Birch tree was planted in spring of 2017. It seems to be thriving but then I have recently noticed that on many branches the leaves are being "eaten". I am attaching photos. RiverBirch1 shows a branch with many leaf "skeletons" RiverBirch2 shows a couple of leaves with dark spots and holes RiverBirch3 shows the top of the tree where most every branch is starting to have skeleton leaves
Your birch tree is still establishing its root system. The three photos show some sawfly (larvae that resemble caterpillars) damage. This pest is long gone and no control is necessary. The middle photo shows some sawfly damage and some leaf spots which is not concerning. The tree should put out new growth next season.
Birches in general have a very shallow root system and require a moist soil. It is not uncommon for them to drop leaves throughout the season. Make sure mulch is no thicker than several inches and keep away from the base of the trunk. Keep the tree well watered during dry periods.
See our publication for more information on birch http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG58_IPM_Birch.pdf