Birch Leaf Minor

Symptoms:  Tiny pale yellow spots first appear in spring on the new leaves followed by brown paper-like blisters.  A small (up to ¼”) whitish larva may be found inside the blister.  It is important to control these insects as they may not only destroy your tree’s beauty, but may also make it more susceptible to bronze birch borers.

Analysis:  When the birch leaves are half grown in the spring, the sawfly lays eggs on the leaves.  When the eggs hatch the larvae feed between the upper and lower surfaces on the leaves causing blisters.  The mature larva chews its way out of the leaf and drops to the ground to pupate.  The adult fly emerges and the cycle repeats itself 3-4 more times in the growing season attacking the newly developing leaves.

Solution:  Larvae are difficult to control once they are protected inside the leaf.  Read and follow all label directions!  We recommend 3 ways to treat.

1.      Treat by spraying (works best for small trees) with Orthene, Malathion, Sevin.  First application should be made in spring as the leaves are unfolding or when the first tiny pale yellow spots first appear.  Spray thoroughly.  Then treat again in early July to control larvae of the 2^nd generation.

2.      Apply Bayer Tree & Shrub Contol  (Imidacloprid) directly to the soil according to directions.  The insecticide is absorbed through the roots and circulates throughout the tree.  Fall applications are the most effective, however, it can also be applied in early spring.

3.      Treat with granular 1 and 2% Di-Syston systemic granules.  Correct treatment will use between 14 and 28 ounces of material per inch of trunk diameter, depending on the formulation.  To apply, measure the needed dosage and distribute equally in eight to twelve holes.  Make the holes four to six inches deep, in a pattern around the tree, midway between the trunk and dripline.  “Heel” the holes shut after application and water the ground thoroughly.

Cultural Control:  Insecticide controls may be more effective if overall tree stress symptoms are reduced.  Trees should be fertilized in spring and fall.  Watering regularly is very important especially during dry periods.  Mulching around the tree base is also helpful to increase moisture retention and cool the tree’s roots.  Selecting a proper planting site is very important. 

Bronze Birch Borer

Symptoms:  Leaves are yellowing and the foliage is sparse at the top of the tree.  Twigs and branches may die, but the leaves on these branches only turn brown, but don’t drop.  There are “D” shaped holes and ridges on the trunk and branches.  Swollen ridges are packed with sawdust.  The first sign of attack is in the upper third of the tree.  Over time, the attack progresses downward to lower branches and trunk.  Typically kills trees in 3 – 4 years.

Analysis:  The birch borer is the larva of an olive-brown beetle.  The feeding and tunneling of the larvae stop the flow of nutrients and water in that area, twig and branch dieback result.  Factors that weaken the tree, such as poor growing conditions, transplanting, and mechanical injury make it more attractive to borer infestation. 

Solution:   Cut out and destroy all dead and dying branches.  Severely infested trees should be removed.  Lightly infested trees often return to full health with a regular preventive insecticide program.

1.      Spray Permethrin (Eight) three times about May 15, June 15, and July 15^th.  Trees must be thoroughly sprayed in order to be effective.  This pesticide does not kill larvae already tunneling beneath the bark, but they prevent succeeding generations from infesting the tree. Water and fertilize as needed.

2.      Apply Imidacloprid as a soil drench near the base of the trunk. Treatment should be made in the fall from late September to early November, for tree trunks larger than 4 inches in diameter at chest height. Smaller trees can be treated in the spring.  Treat only once per year.

Cultural Control:    Selecting the proper planting site is very important.  Plant birch trees in more natural, semi-shaded, moist sites.  Avoid exposed terraces or planting the tree by itself in a sunny, exposed lawn that may lead to water or temperature stress problems.  Birches have a very shallow root system, so keep your trees healthy by fertilizing in spring and fall.  Water regularly during drought periods, or if your Birch tree is planted in light soil.