Recommended Treatments for Common Diseases in Japanese Magnolia Trees

Though the Japanese magnolia tree finds its origin in Japan and China, it is now a popular ornamental in European and North American countries. The tree has a small stature even once it has reached full growth, and it usually has multiple trunks sprouting up from the ground in clusters. More eye catching, however, are the flowers that have earned the Japanese magnolia tree its reputation. Petals are large and cupped similarly to those on the southern magnolia, but they differ in color. Rather than white, the Japanese magnolia flower has a delicate pink color.

Leaf Spot

Leaf spot is one of the most frequently occurring fungal diseases to infect Japanese magnolias. Signs of this disease will appear in the form of brownish spots across the surface of leaves. These spots will usually arise during the summer. Leaf spot can cause the plant to shed leaves and eventually suffer significant structural weakening. As soon as you notice the spots, you need to prune back any branches affected. You should also purchase a fungicide to eliminate the problem if it appears to be worsening. A good fertilizer may help prevent leaf spot in the first place, but it is typically not a 100 percent effective measure of prevention.

Verticillium Wilt

Verticillium wilt is a fungal disease that sometimes infests Japanese magnolias. Initially, the leaves will yellow and wilt. Progressive damage can cause the limbs of the tree to die. If your tree has verticillium wilt, a fungicide will help you manage the damage, but it will not get rid of the cause. Since the soil is where this fungus develops, the best course of action is to fumigate the soil. And since the disease cannot totally be eliminated, once the tree becomes infected, you are best off to destroy the tree, completely remove its remains, apply a fumigant to the soil and plant a new tree.

Sooty Mold

Sooty mold is not as common on Japanese magnolias as other diseases, but it still crops up occasionally. You will notice a sticky, black coating on leaves and spots on branches. As long as the problem is not too extensive, you'll only have to worry about the tree's appearance, but enough of the mold can obstruct photosynthesis in leaves and lead to the leaves dying or growth of the tree being affected. Good fertilization can prevent the disease, and at its first signs, pruning affected areas is the best magnolia disease control method. The fungus that causes sooty mold thrives on secretions left behind by insects such as aphids. An insecticide for aphids could help in management.

Cankers

Different types of cankers can become problematic for Japanese magnolias. Cankers may be bacterial or fungal in origin, but in the case of the Japanese magnolia, cankers are almost always fungal. They can be identified as small, knotlike areas along tree limbs where plant tissue has begun to die. They are not pretty to look at, and in some cases they can deform or kill a tree. If you notice any cankers on your Japanese magnolia, you should prune back the limbs they appear on and apply a fungicide as a control method.

References

• University of Florida IFAS Extension; Magnolia x Soulangiana; Edward F. Gilman; May 2007
• University of Illinois Extension; Fungal Leaf Spot Diseases of Shade and Ornamental Trees in the Midwest; July 1998
• University of Minnesota Extension; Cankers on Trees; Connie Reeves; January 1999
• University of Minnesota Extension; Verticillium Wilt of Trees and Shrubs; Cynthia L. Ash; 1994
• UC IPM: Sooty Mold; F.F. Laemmlen; July 2011