Question
Mr. Hyland,  We have a 14 yr old river birch which has been quite healthy and growing nicely.  I've notice now that some of the leaves have a pink residue on them.  Also that some of the leaves seems to have a yellow-green striping to them.  What could this be?  We live in Minnesota.  We have 2 river birch trees and the other one has it as well.  I would appreciate any info you would have on this problem. I love the trees and want to have them healthy.  Sue

Answer
Sounds like birch leaf miner. The birch leafminer, Fenusa pusilla (Lepeletier), is a small sawfly native of Europe that was first detected in Connecticut in 1923. It has since spread throughout northeastern North America. The larvae of the sawfly make blotch mines in the leaves of most birches

Damage to birch trees is done by the larval stage as it feeds between the upper and lower layers of the leaves. This feeding produces large blotch mines in the leaves. Often, several larvae will completely mine a single leaf. Multiple generations and high populations can cause damage to almost every leaf by mid-summer. The mines turn brown and will cause the tree to look dead with wilted brown leaves. This forces the tree to refoliate and reduces its ability to produce food for growth. This damage may also make the trees more susceptible to bronze birch borer attack. Though the adult birch leafminers are related to wasps, they do not have a sting.

Here is a web link that gives more information with pictures and control measures for this insect.  

http://woodypests.cas.psu.edu/factsheets/InsectFactSheets/html/Birch_Leafminer.h...