Things Going On

There are a couple of things going on here, not necessarily related. 1. The bumps are galls. These are caused by insects or mites that lay eggs in the leaf and then the leaf-tissues grow around the developing critter, altering the cellular growth of the leaf to protect what’s growing inside. Although this looks creepy, it’s seldom harmful to a tree. Read more about galls here: http://bit.ly/1pJ4ZPe 2. There is also some leaf spot on this foliage, most likely caused by a fungus. Again, this is a cosmetic issue and seldom harmful for the tree. Read more about leaf spot fungi here: http://bit.ly/1oRng0w 3. Finally, it appears that you might have a nutritional problem with this birch, most likely an iron deficiency either because your soil lacks iron or because the soil is alkaline so the tree can’t uptake the iron that is there in the soil. You might want to have a pH test done of the soil around this tree before doing anything like adding iron…if the pH is off no amount of iron will help. You can read more about this issue by going here:
http://www.extension.umn.edu/garden/diagnose/plant/deciduous/birch/leavesyellow.html