Is this something I need to address?
Hi - These symptoms on your river birch are indicative of an aphid infestation. Check the back of the yellowing leaves, which is where the aphids would be feeding. Spiny Witch Hazel Gall Aphid (Hamamelistes spinosus) is a common but not serious spring pest on river birch trees. It then moves to witch hazel to complete its life cycle. You can learn more about it on this page from our website: https://extension.umd.edu/hgic/topics/shade-tree-galls#spiny
There are natural predators of aphids (ladybird beetles, lacewings) that tend to show up when aphid populations increase and they help to manage pest populations naturally. Please see our website about aphids and biological control as well as other management recommendations, https://extension.umd.edu/hgic/aphids-trees-and-shrubs
On the willow oak, we do not see symptoms of a pest or disease issue. Since it is newly planted, it is going to need time to establish a good healthy root system to support the canopy growth. So one of the most important things to do in the first 1-2 years after planting is to pay close attention to the soil moisture and water when the soil feels dry to the touch. You should check the soil at least once each week. Probe the soil with a screwdriver or hand trowel to check if it feels dry to the touch. If it does, water right at the base of the trunk area and deeply. Refer to our website for guidelines on watering new trees, https://extension.umd.edu/hgic/topics/watering-trees-and-shrubs.
Also, make sure the mulch (if you have mulch down) is not too deep. It should be no more than about 3" deep and avoid placing it directly against the trunk. A correctly planted tree should have a visible root flare right at the soil line. https://extension.umd.edu/hgic/topics/mulch