Last year we treated our magnolia for scale and this year there are white bugs crawling all over the tree. Are these scale?
Thank-you for contacting Toronto Master Gardeners with your question. It is such a worry to find a beautiful magnolia tree undergoing an insect infestation.
Magnolia scale and the related mealybug go through several stages during their annual life cycle. A few of these stages can look quite similar to your image. The scale was the more likely choice since you were battling that recently, but the descriptions I found in my research did not fit in terms of appearance and expected timing of the nymph stage (the females do not usually get to be this large until later in the summer). The following article includes some useful descriptions and photos of magnolia scale:
Then I came across an article with the image below. This insect looks just like your photo to me. This is the nymph stage of a ladybug (Hyperaspis) that feeds on scale insects. I suspect that the insects you are seeing are feeding on this year’s generation of scale nymphs – survivors of the treatment your tree underwent last year. If this is correct, they are actually beneficial to your tree and you will see them pupate and transform into adult ladybird beetles fairly soon. Have a look at the full article I have linked to here:
If this is an incorrect identification, and the insects you are seeing are a phase of the scale from last year, you will need to repeat some kind of scale treatment later this summer. Either way, your best course of action is to continue to observe your tree closely. Even if the insects in the photo are ladybugs, they may not be numerous enough to control a further scale infestation. You may still need another treatment.
Hopefully you will find that you are receiving some help from the insect world!