Birch Decline

Ornamental birches are beautiful trees widely planted in southern Idaho.  Attractive as they are, before you plant one in your yard there are a few problems you should consider.

First and foremost, birches require a great deal of water.  In our dry climate this will require frequent, deep irrigations.  If the plants run drier than they need, they will be placed under stress and be more susceptible to several common birch tree problems.  Proper irrigation is the most important aspect of birch health.  Water and fertilization, if needed, will help keep the trees vigorous.

One common birch problem is birch dieback caused by the Nectria fungus.  This fungus invades trees through wounds and injuries including winter injury, damage from drought, sun scald, leaf scars, cracks in the swigs, or dying lower branches.  The spores of this disease spread in rainy weather.  The signs that your tree is suffering from dieback include dying twigs, limbs, and sometimes trunks.  The actual fungus is not obvious most of the time.  Control includes removing and destroying affected twigs and limbs.  Be sure to sterilize pruners between cuts to avoid spreading the disease.  Prune during dry weather.  Do not leave stubs by pruning back to a branch of some type.  Applying a fungicide after pruning may protect against further infection.

The next problem to consider is the bronze birch borer.  This insect usually moves into a tree weakened by drought or dieback.  The adult is a one half inch long beetle with a blunt head and tapering body.  The larvae are flathead borers.  Cut leaf varieties of birch are particularly susceptible to attack by this borer.  You will see little holes in the trunk or limbs where the borer has entered or exited.  Control involves an insecticide spray to the trunk and lower limbs, keeping the spray off the leaves if possible.  Do this in late spring, when the adults are active.

            Whether or not birch trees are under stress, they will probably be attacked by the birch leaf miner.  This is a small black sawfly whose larvae tunnel just under the surface of the leaf making pale blotches of varying sizes and shapes.  Once you see the damage it is too late to avoid damage, but since there are several generations of flies a year, at least you can stop the spread with a chemical spray.  To avoid damaged leaves completely, apply insecticides in late spring when the new little leaves are fully formed.  A second application should occur about a month later.

            Two other insects to be on the lookout for on birches are oystershell scale and aphids.

            With all the problems involved, you will want to think twice about planting a birch.  If you make a commitment to keep it well watered and vigorous, you can grow a healthy, beautiful tree in spite of all these common problems.

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