Birch Leafminer

Fenusa pusilla

Birch leafminer is the larval stage of a small “fly-like” wasp, Fenusa pusilla. The larvae feed between the epidermal layers of a leaf and are protected from predators and parasites by the leaf. Once damage is obvious, it is usually too late to treat as the larvae leave the mine to pupate. Control measures need to be systemic or be timed to coincide with early larval feeding before damage becomes apparent.

Download Birch Leafminer Fact Sheet

Treatment Strategy

Treatments for birch leafminer are effective, and will also protect the tree from bronze birch borer. Which product to use is determined by the time of year treatment will be applied.

Minor infestation of leafminer does not affect the health of the tree or the appearance. Major infestations will cause the whole tree to look brown and compromise its ability to make sugars in the leaves which can compromise health.

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Birch Leafminer Treatment Option 1

Optrol™ is extremely effective against leaf miners because it works where insects feed. It does need 30 days to reach the leaves, so it needs to be applied very early in the spring to control current season leaf miners or in the late summer through fall for control next year. Most arborists use Xytect™ as a fall application to effectively control leafminer in the spring. Xytect™ is very easy to apply and can be drenched at the base of the tree. It provides 12 months of protection.

Application Type – Soil drench

DIY Product/Equipment Needed:

Optrol™

• Soil Drench Kit

• Measuring or diameter tape

• Bucket or watering can

• Measuring cup

• Gloves

Birch Leafminer Treatment Option 2

Treatments done later in the spring require a faster insecticide. An effective last minute treatment is Transtect™. Transtect™ takes aboiut 2 weeks to move from the soil into the leaves, controlling leaf miners as they are feeding. Apply Transtect™ soil applications in the spring to control emerging leaf miners.

Application Type – Soil drench

DIY Product/Equipment Needed:

Transtect™

• Soil Drench Kit

• Measuring or diameter tape

• Bucket or watering can

• Measuring cup

• Gloves

Birch Leafminer Treatment Option 3

Cultural practices such as watering and low nitrogen fertilization can help affected trees regain vigor.

Birch Leafminer DIY Kit

Option 1

Application Type – Soil drench

DIY Product/Equipment Needed:

Optrol™

• Soil Drench Kit

• Measuring or diameter tape

• Bucket or watering can

• Measuring cup

• Gloves

Option 2

Application Type Soil drench

DIY Product/Equipment Needed:

Transtect™

• Soil Drench Kit

• Measuring or diameter tape

• Bucket or watering can

• Measuring cup

• Gloves

How Is It Spread?

• Pupae overwinter in a cocoon 1-2 inches under the soil

• Adults emerge in spring (March-May)

• Mated females lay eggs in leaf (April-May)

Larvae produce a blotch mine (April-June)

Larvae form a pupation chamber in the soil (May-June)

Susceptible Trees

All birch species (Betula)

Symptoms

• Large blotch mines in the leaves

• Damage is scattered throughout the tree

o Mines will turn brown

o Leaves will look wilted

• High populations can damage the entire canopy

• Repeated defoliation by leaf miner will decrease tree health

• Leaf miner defoliation is directly correlated to Bronze birch borer attack

Lookalikes

Drought; bronze birch borer.

Related/Similar Problems

Bronze birch borer

Timing

Spring or fall

Urgency

Low

Risk of Spreading

Moderate

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