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Birch Problems

June 28, 2000

We have many inquiries at the Plant Clinic concerning birch trees that are stressed. The complaints usually follow this scenario: The birch leafs out normally in the spring, then all of the leaves on a branch or two quit growing, wither, and die. Eventually the affected branches die, too. Often the tree has yellow-green leaves with branch-tip death.

Many diseases of birch exist, but few that cause the dieback symptoms described. Leaf blights do not cause such injury, nor do viruses or wood rots. Potential pathogens involved in this decline are the canker fungi (Botryosphaeria, Nectria, Physalospora, Diaporthe, and many others) and a dieback disease caused by a fungus named Melanconium. The dieback disease is actually closely related to canker problems. In all cases, the tree is infected when under stress. Melanconium dieback is known to cause a progressive dieback of upper branches, especially following periods of drought. We certainly had drought conditions last summer, fall, and winter to set up the decline process. The canker fungi could also infect trees predisposed by drought, injuries, flooding, borers, and so on. Usually more than one factor is involved, and it is impossible to determine which factor started the decline.

Michael Dirr in his book Manual of Woody Landscape Plants says that most birches do best in well-drained, acid, moist, and sandy or silty loam soils. He states that he would not plant a river birch (Betula nigra) unless the soil pH were 6.5 or below. Some birches are more adapted to a variety of soil types and moisture levels, but they will become very chlorotic in our high pH soils.

Each birch in decline is different because the stress varies with each tree and the particular site. There is no current disease epidemic on birch. In most cases, it appears that early drought stress compounded by high pH soils has probably stressed these trees, predisposing them to infection by canker and dieback fungi. There is no easy cure. Remove dead limbs to avoid problems with wood rot. Water the trees in periods of drought stress. Test the soil and find out what pH level your tree is growing in so that you can determine whether an acidic fertilizer is needed. Look for cankered areas on the wood, and remove these where possible. Last, do some research to find out the particular needs of the birch species you have planted. If you are planting a new birch, do the research first.

Author: Nancy Pataky


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