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Description

There are two species of elm leafminers in Grande Prairie:

  • Fenusa elm leafminers (Fenusa ulmi) damage elm leaves during June and July.  Their feeding damage crosses leaf veins, leaving large portions of the leaf brown and papery thin.  Larvae are 4-5mm long and adults are small, black, stingless wasps.  As yet, these leafminers have only been found on Siberian elm in Grande Prairie.
  • Agromyzid elm leafminers (Agromyza aristata) are active in May, almost as soon as the leaves emerge.  They cause substantially less damage than Feunsa leafminers, since they create serpentine galleries, which don't generally join together but wind their way through the leaf.  They are also smaller larvae than Fenusa, only 2-3mm long.  Adults are small flies.  These leafminers are found on both species of elm in Grande Prairie.
Agromyzid Elm Leafminer
The characteristic serpentine gallery made by an
Agromyzid elm leafminer

 Fenusa Leafminer

 Fenusa elm leafminers produce large, sac-like mines
and can cause widespread defoliation of Siberian elm
trees. 

Plants Affected

Symptoms

Watch for mining activity within elm leaves beginning in May.  Agromyzid leafminers rarely cause severe damage, as their mines are so small.  Fenusa leafminers can cause severe damage to trees in high populations, as their mines destroy large portions of leaf surface.

Controls

Cultural or Non-chemical Controls:

  • Agromyzid elm leafminers cause so little damage that no controls are necessary.
  • If only a few leaves are affected by Fenusa leafminers, they may be picked off and destroyed.  

Chemical Controls:

  • A chemical application may be warranted in May (targeting the emerging adults) if the entire tree is heavily infested.

For more information on chemicals available for control of these pests, call Agriculture Canada's Pesticides Directorate in Ottawa (toll-free) at 1-800-267-6315. Chemical pesticides may be toxic to humans, animals, birds, fish, and beneficial insects. Follow all label instructions and precautions listed by the manufacturer.

Last updated: 12/15/2014 7:46:13 AM