Diseased Magnolia Trees
There are four magnolia trees in a courtyard island. Two out these four magnolias died within three years. The replacement magnolias showed signs of affliction soon after planting. I do not know what variety the magnolia trees are but they are small (about 7”), with irregular spread, and have creamy white or white flowers. Symptoms typically appear in mid spring and progress through late summer. Leaves initially show yellow spots that later become brownish and many of them develop shot holes. Some leaves show signs of distortion and irregular marginal browning/scorching. (Picture Nr.1). Very few leaves show a specific pattern of discoloration or grayish spotting that reminds of a map design (Picture Nr.2). These leaves will wilt, die and ultimately fall from the branches. Flowers, which are typically white, initially develop brownish spots (Picture Nr. 3) and then turn brownish in totality and die. Please diagnose the problem and indicate remedies. If there is a need to send specimens to a lab/clinic for diagnosis, please indicate the lab’s name and address. Thanks a lot for your help.
We would like to have more information. Please send us photos of the whole tree, around the base of the tree, and affected foliage so we can see what you are dealing with. Also, we would like to see photos of the courtyard island and where the plants are located. Are they in full sun, shade, and how are they cared for, etc.
The middle photo shows an insect called a leafminer and seldom causes damage to the tree, mostly cosmetic damage.
Thank you very much for your help. Per your request, I am providing more information and pictures.
Most of the day magnolias are in full sun. They are in the shade of a larger tree (which is pretty far from them) only after 4:30 - 5:00 PM. Right now, their overall appearance is nice. However, typically, as the summer progresses their condition worsens – and this is what I would like to prevent. Picture #3 shows how the youngest magnolia looked at the end of last summer, and this is how all of them typically look as the problem/affliction progresses. Sometimes full branches dry up and die. Usually they retain most of their leaves year-round but last fall/winter they lost all of their foliage. The soil is clay. There are old junipers in their proximity. Mulch is layered around their bases each spring. During dry summers with temperatures over 85-90 degrees I deep water them twice a week. Thanks again, Alex.
The symptoms seem to be rather uniform throughout the plant, so it is probably an abiotic (environmental) factor - not a disease or pest issue. Do some soil excavation to see if materials were left around the root ball when the plant was installed. It also looks like it was planted very deeply, which can contribute to decline. This species can tolerate wetness well, but it won’t do well in extremely dry conditions, particularly if the roots are confined to a very small space. Pull back the mulch. It should be no deeper than 2-3" and it shouldn't be placed right up against the trunk.