infestation of magnolia tree ?
Hi - was in the yard today and noticed on my new magnolia tree (planted last fall, approx 10 ft tall) and immediately saw that something was not right. Initially noticed that many of the lower leaves had black discoloration, which when rubbed was quite slimy and came away from the leave. On closer inspection I saw some red nodules on the branches of the tree. Some of the nodules are isolated, others are clumped together in large groups. Appreciate any advice you may have
Your magnolia has tuliptree scale insects on it. Scale insects have a shell, like a turtle, that protects the body of the insect underneath. Tuliptree scale are very large, for scales. They suck sap from the tree and large infestations can kill a tree. They also excrete a sugary substance called honeydew, which lands on leaves and twigs below them and in which a fungus grows that turns it black--hence the "sooty mold" you saw.
They lay eggs under their covers to protect the eggs. You cannot spray effectively at that time. But, when the eggs hatch and "crawlers" emerge, you can spray the unprotected crawlers. You can look under the cover and see if they have eggs until they hatch, then spray with an insecticide containing pyrethrins or spray with horticultural oil or soap (read label carefully for temperature limits!) This is usually in September, but could start in August.
A much simpler approach for you, since the tree is still small, is to manually squish all the scales on the twigs and branches. There is only one generation so that should take care of it.
Here is info about scale control : http://extension.umd.edu/hgic/soft-scales-trees-as nd-shrub