A2117

URBAN PHYTONARIAN SERIES

Birch (Betula)
Disorder: Birch Leaf Miner
Phil Pellitteri

Birch leaf miners are insects that can destroy leaves of all ornamental birch varieties grown in Wisconsin. While European, white, gray and paper birches are most susceptible, yellow and river birches are also affected. Not only do these insects destroy your tree's ornamental beauty, but repeated birch leaf miner attacks weaken your birch trees' resistance to bronze birch borers.

Symptoms and Life Cycle Birch leaf miner larvae overwinter in cocoons combined with soil particles one to two inches below the soil surface. They emerge in early May as black sawfly adults about 3/16 inch long, and females deposit eggs only in new expanding leaves. Larvae do not develop in mature leaves. Small, flattened, white larvae appear seven to ten days later. The first symptoms of birch leaf miner attack are the feeding marks from the young larvae -- small, blistered, translucent spots on new leaves. For 10 to 12 days they mine leaves, consuming tissue between the upper and lower leaf surfaces. Leaves turn brown and paper-like and finally drop off. After 10 to 15 days, the mature larvae cut a hole in the leaf, fall to the ground and pupate. During the summer they spend 15 to 20 days in the soil and re-emerge as adults. They repeat this cycle producing three to four generations from May to August. The first or spring infestation of birch leaf miner is the most serious. All of the leaves can be affected, making the tree look blighted. Weakening of the tree at this time also increases the chances of bronze birch borer injury. Because the birch leaf miner attacks only new foliage, each succeeding attack becomes less severe and damage is frequently limited to tree tops or newly developing leaves on young sprout growth.

Birch leaf miner injury. The three affected leaves are light brown and papery.

Control

Cultural

There are no non-chemical controls for this pest at this time. Several natural enemies live in Wisconsin but are not abundant enough to reduce infestations to acceptable levels. Research into the pest's natural predators and parasites in its native home (Europe) is needed with the possible goal of importing additional natural enemies.

If you do not use chemical controls, be sure to maintain tree vigor and reduce injury by other pests.

Chemical

You can control the insect with chemical sprays if you apply them thoroughly when the first, tiny pale yellow spots appear on leaves in spring. Controlling the spring generation is critical for maintaining tree health and tree appearance. Use one of the following insecticides on the foliage:

Homeowners

Note: Check the formulation you purchase. Dosage will vary for different formulations.

An alternative method of controlling leaf miner involves applying a granular systemic insecticide to the soil. The granules release insecticide which is absorbed through the roots and circulates with the sap throughout the tree. The treatment kills any leaf-miners or other insects that feed on the leaves, but does not affect beneficial insects. Apply granular systemic insecticides in early May, before the tree begins growth. The applications must be followed by rain or watering.

Di-Syston 1 and 2% granular formulations, and a l% granular plus fertilizer are available for homeowners at this time. Additional granular systemics may appear on the market in the future. The amount of Di-Syston to use depends on the tree size. Correct treatment will use between 14 and 28 oz of material per inch of trunk diameter, depending on the formulation. This treatment is moderately expensive but reducing the recommended amount will not give sufficient control.

To apply, measure the needed dosage and distribute equally in eight to 12 holes. Make the holes four to six inches deep, in a pattern around the tree, midway between the trunk and dripline (see illustration). "Heel" the holes shut after application and water the ground thoroughly. Because leafminers must feed for a short time before the chemical takes effect, heavily attacked trees you have treated with a systemic may show several small yellow dots on each leaf. These dots are egg-laying sites where larvae have hatched, and begun to feed before being killed. Only commercial growers or professional applicators should use the 15% granular formulation of Di-Syston.

Commercial Applicators

*Commercial Applicator Only

References to pesticide products in this publication are for your convenience and are not an endorsement of one product over other similar products. You are responsible for using pesticides according to the manufacturer,s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.

Author: Phil Pellitteti is a specialist in the Insect Diagnosis Laboratory, Department of Entomology, College of Agricultural and Life Sciences, University of Wisconsin-Madison and University of Wisconsin-Extension, Cooperative Extension. Produced by the Department of Agricultural Journalism, University of Wisconsin-Madison.

This publication is available from your Wisconsin county Extension office or from: Agricultural Bulletin, Rm, 245, 30 N. Murray St., Madison, Wisconsin 53715, Phone 608-262-3346. Contact Agricultural Bulletin to determine availability before publicizing.

University of Wisconsin-Extension, Cooperative Extension, in cooperation with the U.S. Department of Agriculture and Wisconsin counties, publishes this information to further the purpose of the May 8 and June 30, 1914 Acts of Congress; and provides equal opportunities in employment and programming including Title IX requirements.

A2117 Birch (Betula) Disorder: Birch Leaf Miner, 1990 R-08-90-3M-60-S

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