Small Bumps on Leaves and Branches
Scale Insects - Scale insects are sap suckers. They live beneath shiny brown waxy scales or covers that appear on leaves and stems as small bumps. Although about 10 different scale species attack magnolia, Magnolia scales are a major pest of these trees. They are the largest American scale species, up to 1/2 inch in diameter, with a white covering. Heavy infestations of scale cause underdeveloped leaves and generally weak trees. Young scales appear in late summer. The bumps are visible in the winter on the bare trees. For more information see the file on Controlling Scale
Leaves Spotted; Drop Prematurely
Leaf Spot - Leaf spot diseases caused by various fungi attack magnolias. They're distinguished by yellow, brown or black dead blotches on the foliage. Often spots come together to form larger patches of dead tissue. Heavily infected leaves fall prematurely. Gathering and destroying fallen leaves usually suffice for practical control in established, mature trees. For more information see the file on Controlling Fungal Disease
Brown Spots on Flowers; Torn Leaves
Weather - Frost Damage: Early blooming magnolia trees run the risk of damage by spring frosts in the North. Flowers that are marred by brown blotches on the petals, or are totally brown and mushy have been affected by frost. There is no permanent damage to the tree or bud formation and flowering next year.
Wind Damage: Evergreen bigleaf magnolia leaves, up to 3 feet in length and 7 to 12 inches wide, are easily torn by whipping winds. Site this and other large leafed magnolias in a protected location.
Bark Cut or Bruised; Growth Stunted
Cultural Problems - Equipment Damage: Young magnolias have very thin bark that is easily damaged by lawnmowers and string trimmers. To protect tree trunks from injury from yard care equipment, spread the recommended 2 to 4 inch layer of mulch or plant groundcover plants around them out to at least 2 feet. This will both discourage weeds and grass from growing near the tree trunk in the first place and prevent equipment from coming to close to it.
Black Walnut Neighbor: Magnolias suffer stunting, wilting, or even death when they grow into the root zone of a black walnut tree, or even a stump. The walnut's roots exude a chemical (juglone) that inhibits or prevents other plants from growing. A toxic reaction occurs within a circle 1.5 times the distance from the trunk to the outermost branches of the walnut tree. Do not plant magnolias close to black walnuts.
Leaves Stippled; Covered with Webs
Spider Mites - These spider relatives are about 1/50 inch long, barely visible to the unaided eye. They have four pairs of legs, piercing-sucking mouth parts, and very compact bodies. Spider mites may be yellow, green, red or brown. Watch the lowest leaves on the young magnolia tree. Stippling of small yellow dots or red spots on the tops of the leaves, or fine webbing that distorts leaves and adjacent stems indicate the presence of spider mites. For more information see the file on Controlling Mites
Leaves Pale; Coated with Honeydew
Whiteflies - Whiteflies are tiny, white-winged, mothlike insects that suck plant sap. They are about the size of a pinhead and stand out on the dark green magnolia leaves. Infested trees weaken, and the leaves turn yellow and die. The leaves may be covered with shiny, sticky honeydew secreted by whiteflies, and a black fungus that is encouraged by the honeydew. While they will not seriously harm a mature, well-established magnolia tree, they can take a toll on the vigor of a young one. For more information see the file on Controlling White Flies
Holes in Leaves
Caterpillars - Some kinds of caterpillars will attack magnolias, although they are not as vulnerable as most trees to these pests. On the West Coast, the omnivorous looper caterpillar is a magnolia pest. In the East it is the saddleback caterpillar, which has a distinctive saddle-shaped patch on its back and is armed with poisonous spines on each end. For more information see the file on Controlling Caterpillars
Lesions on Stems/Trunk; Foliage Thins; Dieback
Fungal Disease - Nectria canker produces rounded, target-like lesions (cankers) on magnolia branches and trunks. They eventually are girdled by the cankers and die.
A heart rot sometimes attacks magnolias. Affected trees show sparse foliage and dieback of the branches. Early on, the rot is grayish black, with distinct black lines near the advancing edge of decay. The mature rot is brown. The disease is incurable once it has infected large areas of the trunk.
Prevent fungal diseases by avoiding bark injuries, by promptly treating injuries that do occur and by keeping the tree healthy by fertilizing and watering. For more information see the file on Controlling Fungal Disease
Dead Leaves Matted Together
Leaf Blight - Sometimes a leaf blight disease, caused by a fungus, covers magnolia leaf undersides with matted fungal threads. Leaves die early and hang matted together from the twigs for some time. Prune out and destroy infected branches. Then disinfect your pruning tools by dipping them into a solution of hot water and household bleach. For more information see the file on Controlling Fungal Disease
Leaves Turn Brown and Collapse
Verticillium Wilt - A wilt disease caused by the soil-dwelling verticillium fungus sometimes attacks magnolias. Infected leaves appear pale and wilted, and may fall prematurely. One or more branches wilts suddenly and dies. Sapwood is discolored. Heavy feeding with high-nitrogen fertilizer sometimes helps trees surround the infection with a new ring of sapwood, and they may then survive. Prune out dead branches. Remove badly infected trees, together with as many roots as possible. Do not replant with wilt-susceptible shrubs or trees in the same location. Replace the magnolia with resistant species which include: most conifers, beech, birch, boxwood, dogwood, fruit trees, holly, locust, mulberry, oak, pecan, serviceberry, sweet gum, sycamore, walnut, and willow. For more information see the file on Controlling Fungal Disease