Disease on our magnolia tree
Our 12-year-old magnolia tree shows diseased branches (see attached photos taken on Oct. 19). What is it suffering from? Magnolia scale disease? And, most importantly, what do you recommend we do? Many thanks.
Another option would be to use a chemical insecticide. Imidacloprid is a systemic insecticide applied as a soil drench. This insecticide is taken up by the roots and transported throughout the plant where it is ingested by the scale insect. Application can be done in late April through early May or August through September. Read the label carefully to minimize damage to beneficial insects.
Thank you for contacting Extension.
I neglected to respond to one of your main questions: Is this magnolia scale?
Yes, it is!
Very helpful! Thank you. Sadly, the magnolia scale spread onto our entire (big) tree, so it sounds like we'll need to use a chemical insecticide, right?
Just for clarification for the other scenario (smaller spread to be fixed with horticultural oil): does the "monitoring" of the tree in the spring mean locating nymphs emerging from their brown coverings? Do nymphs have then two crawling out seasons per year: one in the spring and one in Aug-Sept? Thanks.
Good questions and sorry to be confusing. To clarify, there is only one nymph emergence time each year, usually in August-September. Monitoring in the spring refers to evaluating your tree, looking for the extent of the scale (easier to see without leaves) and applying a horticultural oil product in an effort to suffocate the nymphs before they hatch. The oil will also help control the nymphs once they hatch so it can be used again in the fall. Follow the application directions on the product of your choice.
If the scale is widespread, you will probably have to apply the oil in the spring and the fall and use a residual pesticides that contain pyrethroids, acephate, or carbaryl.