Cause 'Tam', 'Pfitzer's', and juniper often are deficient in magnesium, and other cultivars may be as well. Competition with calcium-rich growing medium or acid conditions can also produce magnesium deficiency when it is not limiting.
Symptoms In contrast to the twig blight caused by the fungus Phomopsis, which is confined at the outset to one shoot or to one side of the plant and usually kills one shoot at a time, magnesium deficiency seldom kills the plant. It produces chlorotic and/or dead foliage in the center of severely affected plants.
Cultural control Be careful because some junipers, such as J. horizontalis, prefer a pot pH of around 5.5.
- Apply Epsom salts (magnesium sulfate) to soil at 1 cup/100 sq ft.
- Foliar application of Epsom salts at 5 oz/gal water (40 g/l).
Reference Hartley, D.E. and R.L. Ticknor. 1964. Magnesium deficiency in juniper. Oregon Ornamentals and Nursery Digest VII:2.