What Causes the Leaves to Yellow on a Japanese Magnolia?

Magnolia blossoms come in many colors.

Japanese magnolia trees are medium-sized magnolias that produce large flowers in the spring. The flowers come in a variety of colors, ranging from white and pink to yellow and purple. Keeping Japanese magnolia trees healthy makes it more likely that the tree will put out showy blossoms that cover the whole tree. Yellow leaves on a Japanese magnolia indicate a health problem.

Drought

Japanese magnolia trees are not resistant to periods of drought, which damage the tree over a short period of time. Allowing the magnolia tree to go without water weakens the tree's leaves and prevents it from taking in nutrients from the soil. Yellow leaves are a sign of dehydration in Japanese magnolia trees. Over time, the leaves will turn brown at the tips and edges. Water the Japanese magnolia regularly to keep it healthy and growing.

Overcrowding

Japanese magnolia trees have crowns that are up to 25 feet wide when they reach maturity. This means that their root system covers roughly the same area under the soil. Planting Japanese magnolias too close together, or planting other trees or large shrubs near a Japanese magnolia, leads to competition among the plants for water and nutrients in the soil. Overcrowded plants produce stunted growth and weak, yellow leaves.

Scale Insects

Although relatively resistant to many types of pests, scale insects are a problem for the Japanese magnolia tree. Scale insects are small black beetlelike sucking insects that feed on the sap of the leaves of the Japanese magnolia. These insects also spread disease, bringing sooty mold to the Japanese magnolia tree. As scale insects feed, they cause the leaves of the magnolia tree to turn weak and yellow. Treat scale insect problems with pesticide sprays to control the population of the harmful insects.

Fungal Disease

Japanese magnolia trees are susceptible to fungal diseases, including verticillium wilt, which is a soilborne fungus that is fatal to the Japanese magnolia over a period of several years. Although you can slow the progress of verticillium wilt with proper pruning, the application of fungicides and the maintenance of the tree's growing environment, verticillium wilt is fatal to Japanese magnolias. One symptom of this fungal disease is the yellowing, wilting and early death of leaves; other signs include leaf curl and branch dieback.

References

• University of Florida IFAS Extension; Alexandrina Saucer Magnolia; Edward F. Gilman; October 1999
• University of Florida IFAS Extension: Japanese Magnolia
• University of Illinois Extension: Magnolia Scale
• University of Illinois Extension: Verticillium Wilt

Resources

• Texas A&M University: Magnolias