Magnolia tree disease/fungus

Asked July 21, 2019, 1:29 PM EDT

My magnolia tree has white fuzzy looking spots on the branches and the leaves are turning black. It is dripping a blackish liquid onto the plants below and their leaves are blackish. Can you identify this for me and recommend a treatment that will not hurt pollinators

Genesee County Michigan trees and shrubs sustainable gardening and landscaping insect issues

1 Response

Hello,
This is an infestation of Magnolia scale on your tree. The scale insect sucks sap from the branches of the tree, and secretes honeydew, a sticky sweet substance that attracts wasps and ants. It also supports the growth of sooty mold which is the black substance you are seeing on the leaves. Scale insects protect themselves under the white waxy armor, which is the fluffy stuff you are observing. Scale insects lay their eggs under this armor, but when the eggs hatch, the immature scale insects move out from under the armor. At this stage, they are called crawlers, and are vulnerable to treatment. This crawler stage usually happens in late August through September, so you should keep an eye on the branches for this activity and time your management for this time.

Insecticidal soaps and horticultural oils are good choices to control these immature "nymphs". These products have little impact on pollinators and other beneficial insects. You may also want to spray the tree with dormant oil in the early spring before bud break to control any insects that overwintered on the tree.

I will attach an article on Magnolia scale, as well as an article on less toxic options to pest control.

https://extension.psu.edu/less-harmful-pesticides

https://www.canr.msu.edu/news/check_magnolias_for_magnolia_scale_now

I hope this is helpful!
Ruth