We have an old magnolia tree and just a few days ago noticed mild magnolia scale infestation.We watched aome videos (from states) , which recommended using “Tree and Shrubs” liquid for treatment. Apparently this doesnt exist in Canada. I would appreciate any recommendations.
Thank you for contacting Toronto Master Gardeners. Magnolias are beautiful but not when covered with scales!
Magnolia scale (Neolecanium cornuparvum) has become a big problem across the GTA so you are not alone in trying to deal with this insect. Not only do the insects cause damage to the tree by sucking the tree’s sap, but the dripping sap can attract wasps, and the honeydew secreted by the insects can lead to sooty mold!
If you can reach the scales easily, now is the time to scrape them off using a soft, plastic knife. For heights you can’t reach, you can also use a garden hose with a high pressure nozzle to knock the scales off the tree. Avoid using a pressure washer as this can cause damage to the bark. Pruning infected branches can also be effective if the scale is limited to only part of your tree.
The Morton Arboretum has some very specific information about the judicious use of chemically based treatments and when they will be most effective. Namely, they are not effective when used on the scales when they are in the dormant stage (as in your photo); however, using a treatment on the nymphs when they emerge at the end of August to the end of September can help to interrupt the life cycle. The Toronto Master Gardeners website has a number of articles addressing magnolia scale, and specifically this link will take you to some clear instructions on how to use dormant or horticultural oil to deal with the nymphs in the fall, as well as emerging nymphs in the spring.
Given the age of your tree, and I am assuming the height too, I recommend you also contact a licensed arborist to give you specific recommendations for your situation. Landscape Ontario is a helpful resource to locate an arborist near you.
I wish you all the best with this gardening project and I hope your tree continues to bring you many more seasons of beautiful blooms!