Magnolia Tree: Black Branches With White Spots

Prune damaged areas off your magnolia tree.

Magnolias are favorite specimen trees for gardeners to grow for their large blossoms and dark green foliage. You can choose to grow one of more than 80 magnolia species, according to the United States National Arboretum. In fact, even shrub-sized magnolias are available for gardeners who have small yards. Unfortunately, magnolias can sustain harm from improper care, pest infestations or fungal diseases, which can cause their branches to turn black and appear to have white spots.

Fertilizer and Pesticide Injury

Magnolia trees can experience leaf burn if you apply too much fertilizer or improperly spray pesticides. Leaves on the tree exhibit white spots where the fertilizer or pesticide was applied on the tree. Leaf distortion, stunted growth and veins appearing on the margins of leaves are other symptoms of improperly sprayed trees. No specific cure is available if your tree receives too much fertilizer or pesticide. New growth must replace damaged white spotted leaves.

Powdery Mildew

Powdery mildew is a fungal disease that causes powdery white spots on leaves. As the tree declines in health, it will exhibit dead black branches, distorted buds, yellowing of leaves and defoliation. Humid weather conditions often usher in these fungal diseases. It is important for gardeners to check their trees during the spring and summer months for powdery mildew. To prevent future outbreaks of powdery mildew, spray fungicide on the tree.

Aphids

Aphids are soft-bodied insects that suck the nutrients out of magnolia leaves, according to the University of California. A population of white aphids on the tree can make the tree look as though it has white spots. These pests leave a substance a sticky substance called honeydew. Sooty mold spores attach themselves on the branches to the sticky substance and cause the branches to turn black. Pests conduct most of their damage when temperatures are between 65 to 80 degrees Fahrenheit. Apply both an insecticidal soap and fungicide to remove the pests and tree the sooty mold.

Cottony Cushion Scale

Cottony cushion scales are identified for their long white egg sac that is attached to the pest. Egg sacs can contain anywhere from 600 to 800 red eggs. Because these scales suck out the nutrients in branches, leaves and twigs, they cause these portions of the tree to turn black and die. In addition, this scale produces honeydew, which catches black sooty mold. Management consists of traps that gardeners can set out on their magnolia tree that have stick to the cottony cushion scale. Most insecticides do not control these pests.

References

• USDA: Magnolia Questions and Answers
• Cornell University: Cultural Problems
• Cornell University: Powdery Mildew
• University of California: Aphid Management Guidelines
• University of California: Cottony Cushion Scale Management