In its adult form, the Birch Leafminer is a sawfly -- but it is the larvae that really wreak havoc on the Birch leaves. These hungry little Leafminers actually insinuate themselves between the top and bottom of leaves where they munch their way along a serpentine path. As these paths intersect, large portions of the leaves start to turn brown.
|Birch Leafminer Damage
Source: Whitney Cranshaw, Colorado State University, Bugwood.org
You'll typically notice Leafminer activity in the tops of Birch trees -- since the Leafminer mothers choose the tenderest new leaves as the best place for their larvae to survive. Whole sections can turn brown due to Leafminer activity. Though the brown leaves are unsightly, and won't regrow during the same season, Birch Leafminers are not generally tree killers. However, if an infestation repeats itself over several years, the cumulative damage can be too much for the tree to survive.
By the time you are aware of Leafminer activity, it is usually too late to alleviate the damage for the season. As part of an Integrated Pest Management approach, our Almstead arborists recommend early application of controls to prevent the larvae from emerging in the next season.