Leaf Miners

Leaf miners are a nuisance that are more aesthetically displeasing to humans than harmful to the trees. The most common trees effected by this pest are:

Siberian Elm

Bur Oak

Hawthorn

Identification

From a distance the tree canopy will appear to be browning out. With a closer look the individual leaves will look clear or almost translucent. When the leaf is examined in the hand it will be noted that it is actually hollowed out in the middle like an envelope. The top and bottom of the leaf will be intact, but clear, and the center will be filled with little black granules and worms if it is June or early July. A very common statement from our customers is that, "Worms are raining down on us!" This can also happen with Brown Headed Ash Sawfly, however those worms are generally fatter and greener and only attack the fraxinus (ash) species of trees.

Life Cycle

Females lay eggs on the leaf of host plants. The larvae hatch and immediately begin tunneling under the epidermis of the leaf. They feed until just before the pupae stage when they exit the leaf and drop to the ground. After pupae stage they emerge as flying adults and begin the cycle again

Damage

Typically the damage is minor. Because the worms feed on the chlorophyll in the leaf cells severe infestations can be stressful on trees since food production for the tree is diminished. If left untreated for several years of severe attacks trees can become vulnerable to other pests and diseases.

Management

Conventional: The most effective treatment is a systemic insecticide called imidicloprid. Because the worms are inside the leaves they are well protected from most methods of control. Systemic treatments act through the vascular system of the plants themselves and become available to feeding insects in the cells where they feast.

Organic: None known.

Cultural Practices: Proper watering. Annual soil treatments.