Birch leaf miner management

Have the leaves on your birch trees suddenly turned yellow and dried up? Leaf miners may be to blame. In fact, leaf miners are one of the most common pests that affect birch trees in North America.

What are Leaf Miners?

Leaf miners are also referred to as sawflies. These bugs are closely related to bees and wasps and were introduced to Canadian forests from Europe between 1920 and 1960. Birch leaf miners attack all species of birch and have been recorded in all provinces and territories except Nunavut.

What Does a Leaf Miner Look Like?

Adult leaf miners look like tiny black flies and are about three to four millimetres long. The larvae are yellowish-white and have a slightly flattened appearance.

Leaf Miner Lifecycle

Leaf miners spend winters in the soil and emerge as insects in early May. Adult females lay eggs in late May or early June by cutting tiny slits in the birch leaves. When the eggs hatch, the larvae eat the green tissue inside the leaves.

After feeding for several weeks, the larvae drop to the ground, burrow themselves into the soil and form cocoons where they spend the winter. There can be two to four generations of leaf miners a year, depending on the species.

Signs of Leaf Miners

The first signs of leaf miner damage are noticeable in early June. You will first see minor, light green or grey discolouration on the tree’s leaves where the female deposited her eggs. As the larvae feed over several weeks, these spots turn into brown, blistered blotches that increase in size, eventually covering most of the leaf.

Are Leaf Miners Bad?

Healthy trees can withstand light-to-moderate leaf miner attacks. However, heavy infestations can weaken the tree, making it more likely to be attacked by other insects, creating a gateway for fungal and bacterial disease.

Leaf Miner Treatment

Leaf miner numbers have been successfully kept low in Alberta over the past several years by a native parasitic wasp that lays eggs inside the leaf miner larvae. The parasitic wasp consumes and kills the leaf miners when the eggs hatch. However, more aggressive action may be needed if the numbers get out of control.

At ArborCare®, we use a systemic organic pesticide called TreeAzin® to treat leaf miner infestations effectively. This product is made from neem tree seed extracts. It is injected directly into the base of the affected tree, where it’s absorbed by the xylem, carried into the leaf and eventually eaten by the insect. In October 2012, TreeAzin® was granted national registration by the Pest Management Regulatory Agency (PMRA).

How to Promote Healthy Birch Trees

If you notice leaf miners in your yard, do not try to treat them yourself. Chemical pesticides are largely ineffective and can do more harm than good. The best way to keep leaf miners away from your trees is to keep your trees healthy by:

• Watering the area under and around your tree at least once a week during the growing season
• Mulching around the base of the tree to keep the roots cool and retain moisture
• Fertilizing in early spring at the onset of the growing season
• Pruning dead branches in June or July after the leaves have fully developed
• Regularly cleaning up old leaves and debris at the base of the tree

If you suspect a birch leaf miner invasion, contact ArborCare® immediately for a diagnosis and treatment. Your birch tree can be saved from dieback and disease if caught early.

Organic Leaf Miner Treatment in Western Canada

The experienced arborists at ArborCare® know how to identify and treat pests and diseases to keep your trees healthy and happy. If you think your trees, plants, and shrubs may be suffering from a birch leaf miner invasion, we have an organic treatment to remove them without harming the environment quickly. We also offer tree pruning, tree planting and tree removal in Calgary. Contact us today for more information.