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Birch leafminer (Fenusa pusilla) larvae feed on the leaves of various birch tree varieties. The larvae are small and white, and have a flat appearance. The adult birch leafminer is a black sawfly, less than a quarter-inch long.

Pest of the Month: Birch Leafminer


What does it look like?


Birch leafminer (Fenusa pusilla) larvae feed on the leaves of various birch tree varieties. The larvae are small and white, and have a flat appearance. The adult birch leafminer is a black sawfly, less than a quarter-inch long.


In winter, the larvae live in the soil encased in a protective cocoon. The adults emerge in late spring to summer, usually May or June, and lay their eggs on leaves near the tips of branches.


 


Host material and range


Birch leafminers attack a variety of birch trees, including Asian white birch, European white birch, gray birch and paper birch. The pest is found all throughout Europe and North America.


The newly hatched larvae feed in between the layers of the leaves, leaving damaged areas called “blotch mines.” These blotch mines turn the leaves brown, and as they overlap the leaves wilt and die.


 


Current threat


The leafminer can actually attack birch trees to the point of defoliation, killing the leaves from the top of the tree down. This defoliation, when suffered over recurring years, can lead to the loss of the infested trees.


In addition, massive defoliation opens up the infested tree to further attack and damage from other pests and disease threats.


 


Prevention and treatment tips


There are a few possible options for prevention and treatment of birch leafminer infestation.


Tree injections of imidacloprid have been found effective in both treating and fending off leafminer attacks. The insecticide should be applied as soon as infestation is detected, or in late spring or early summer as a preventative treatment.


Additionally, an azadirachtin formulation can be applied to treat and prevent infestation. Azadirachtin is a natural extract of the neem tree seed, and is an anti-feedant and growth disruptor that has been found effective against a variety of defoliating insects including leafminers.


Infested leaves can also be removed and destroyed by hand.


 


What can you do?


Inspect birch leaves for any signs of blotch mines. Before turning brown, the mines will first look light green or white, and you may be able to see the larvae within the leaves.


Infested leaves can be removed, and an insecticide application should be applied to control and treat the infestation.


 


Jesse Lee is with Epic Creative, Wis. Article provided by Mauget, a leader in micro-injection and micro-infusion tree care. Contact Mauget or visit www.Mauget.com to learn more about birch leafminer, steps taken to prevent and control them, and proper treatment application and use.

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