When troubleshooting your magnolia tree, factors to look for that will most likely cause problems include environment, improper care and susceptibility to pests or disease. Though magnolia trees are highly resistant to most illnesses, you should know what symptoms to look for. Since magnolias are early bloomers, for example, protection from extreme cold and proper pruning are essential.
If your magnolia is showing signs of diminished health, always troubleshoot by first determining whether the tree's surroundings are sound. Magnolia trees thrive in rich, well-drained soil with an acid pH from 5.0 to 6.5. Though magnolias can tolerate extremes in soil moisture, an incorrect pH level can wreak havoc on a plant's health. When it comes to sun exposure, magnolia trees need full sunlight to partial shade.
Many magnolia tree cultivars are early bloomers. When plants flower early, they are exposed to the threat of being injured by frost. If you are planning to plant a magnolia tree and live in a colder region, look for later bloomers to avoid frost damage that may destroy blooms and injure other parts of of the tree, according to the Clemson University Extension. Though more established trees will likely bounce back into health, newer trees are less resilient and may benefit from fertilizer or extra watering during drier periods of weather before frost, as recommended by the Iowa State University Extension. Plant magnolias in USDA Hardiness Zones 5 to 8 to prevent exposure to harmful climatic conditions.
Pests and Diseases
Though magnolia trees have good resistance to pests and diseases, they are still vulnerable to infection, particularly if they are not kept in optimal health. Often affected by scale pests, magnolias suffer from magnolia scale (Neolecanium cornuparvum), an insect that is covered by a powdery white substance that its body produces. Visible on the trees, these insects create secondary symptoms by feeding on the tree. Development of fungal infections increases because of the release of honeydew (a sugary substance) on the plant that many molds feed upon. Blackened areas or dead, fallen leaves are a sign of scale infestation. For control, apply an insecticide during the spring season, or when scale insects are still in the "crawler" stage before becoming mature adults, as suggested by the University of Illinois Extension.
Certain magnolia trees are susceptible to fungal infections like verticillium wilt (Verticillium alboatrum and V. dahliae), a disease which begins in the root system and works its way toward the tips of the branches. Expect to see wilted, yellowed leaves that may drop prematurely and in some cases, streaked wood and bark that pulls away from the tree. Outcomes are variable from complete recovery to death. For control, keep plants healthy, pruning tools clean and, in the case of death, remove the entire tree and do not replant within the same space, according to the University of Illinois Extension. No chemical cure is available for verticillium wilt.