RT Journal Article SR Electronic T1 Excess Calcium and Magnesium Associated with Lower Crown Mortality of Pin Oak JF Arboriculture & Urban Forestry (AUF) JO JOA FD International Society of Arboriculture SP 241 OP 248 DO 10.48044/jauf.1992.047 VO 18 IS 5 A1 A. S. Messenger A1 B. A. Hruby YR 1992 UL http://auf.isa-arbor.com/content/18/5/241.abstract AB The ornamental value of pin oak trees is reduced when their descending lower branches die. In the upper Midwest, USA, premature dieback of lower branches is common among pin oak trees planted in soils that are calcareous within 1.5 m of the surface. Of 11 mineral nutrients, only Ca and Mg were more concentrated in the leaves of lower branches than in those found higher in the crown. The Ca concentrations of leaves of lower branches of trees showing dieback were much higher than those from trees without dieback. Small necrotic spots of apparently abiotic origin developed in early summer on either green or chlorotic leaves of lower branches and consistently formed before dieback occurred in the subsequent year. Excessive Mg was closely associated with this condition. Green pin oaks at dieback sites had actively absorbing roots within calcareous C horizons of otherwise acidic soils suggesting a source for absorption of the high concentrations of both Ca and Mg in the leaves. Methods of reducing Ca and Mg uptake are discussed.