Magnolia tree fungus - Knowledgebase Question

Mt Prospect, Il
Avatar for aemanuele
Question by aemanuele
July 12, 2010
Seems all the Magnolia's in our area have developed a strange fungus of sorts, leaves are turning black and every branch has these little white knobs attached to them, the tree is very large and we don't want to lose it but do not know how it should be treated, can you help? Thank you

Answer from NGA
July 12, 2010
Without an opportunity to look at the tree I'm going to have to take an educated guess. I suspect you are dealing with scale insects. The black material is called sooty mold and it develops when insects like scales feed on the fluids within the tissues of the plant. When they do, they exude a sticky substance called honeydew which coats the surface of the leaves directly below them. As the honeydew ages it turns black. The white knobs are the scale insects themselves. While you may be able to control them with insecticide sprays, they have a very hard shell which can protect them from physical contact with the sprays. What you might consider is using a systemic insecticide - a soil drench - which will travel throughout the tree and kill the insects as they feed. It can take sometime before you see a reduction in insects, especially on a large tree, but I think it's the best approach. Look for systemic products such as Merit or Bayer Advanced Tree and Shrub Insect Control and apply according to label directions. Good luck with your eradication project.

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