We have many inquiries at the Plant Clinic concerning stressed birch trees. Complaints usually follow this scenario: The birch leafs out normally in the spring, after which all 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.
There are many diseases of birch but few that cause the dieback symptoms described. Leaf blights do not, nor do viruses or wood rots. Potential pathogens are the canker fungi (Botryosphaeria, Nectria, Physalospora, Diaporthe, and many others) and a dieback disease caused by a fungus, Melanconium. The dieback disease is closely related to canker problems. In all cases, the tree is infected when under stress. Melanconium causes a progressive dieback of upper branches, especially following drought. Conditions last summer, fall, and winter set up the decline process. The canker fungi could also infect trees predisposed by drought, injuries, flooding, borers, etc. Usually, more than one factor is involved, and it is impossible to determine which started the decline.
Michael Dirr, in Manual of Woody Landscape Plants, says that most birches do best in well-drained, acidic, moist, sandy or silty loam soils. He states that he would not plant a river birch (Betula nigra) unless the soil pH is 6.5 or below. Some birches are more adapted to a variety of soil types and moisture levels but become very chlorotic in our high-pH soils. Refer to the Report on Plant Disease, no. 603, “Iron Chlorosis of Woody Plants: Cause and Control,” available in U of I Extension offices or on their VISTA Web site.
Each birch in decline is different because the stress varies with each tree and on the particular site. There is no current disease epidemic on birch. In most cases, it appears that last year’s 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 in periods of drought stress, providing an inch of water per irrigation period. Test the soil and find out pH level so you can determine whether an acidic fertilizer is needed. Look for cankered areas on the wood and remove them where possible. Last, do some research to find out the particular needs of your birch species. If planting a new birch, do the research first.