The powdery mildew on the foliage is a minor issue and is somewhat common on Jane and the other hybrid magnolias belonging to the Little Girl series bred at the U. S. Arboretum in the 1950s. After the tree sheds its leaves this autumn, I'd collect them and dispose of them so no spores overwinter on the foliage. As late as it is in the growing season now, I wouldn't bother spraying the plant. Spraying wouldn't reverse what already is there or make it go away or anything. Spraying works better as a preventive to keep powdery mildew from appearing and getting established. If it bothers you (and I do understand your sentimental attachment to this tree planted in memory of your dear daughter) to think of it spreading more, you could spray with either a baking soda spray or neem oil or a commercial fungicide whose label says it can be used to prevent the spread of PM just to see if you can keep it from spreading more, but there's no guarantee at this point that any spray would prevent its spread (short of removing all the leaves) since it already is established. PM is common on some plants here late in the season when we are having high relative humidity in the air but when the ground itself is pretty dry, particularly on stressed plants or those with poor air circulation around them. Those conditions often exist together in dry autumn weather like we've had this year in most of Oklahoma. Unlike many other fungal diseases, PM doesn't really need wet foliage to thrive.

Thanks, Dawn. I figured that was PM, but wasn't sure if I needed to do anything about it. I'll be sure to follow your advice. What about the other pic? Those little spots on the stems. Is that something to be concerned about?

You're welcome. I don't know what the spots on the stems are. Have you tried scratching one off with a fingernail or something to see if it can be removed? Normally, with little things like that on a tree, my guess would be scale. Possibly it is scale, but it doesn't look like magnolia scale, which is much larger and sort of fluffier looking. There's probably some other general kind of scale that it might be, but that is just a guess on my part. I don't see scale very often so only know the most common ones. If it seems like it is scale, horticultural oil (aka dormant oil) would be the answer, but I'd wait until this week's high temperatures in the 70s have gone by. You normally would apply regular horticultural oi/dormant oill only in the dormant season and I'm not sure when anything here is going to actually go dormant since the weather is so crazy-warm. Or, if you determine it is scale, and you prefer to use a horticultural oil now, you could buy the superfine dormant oil, sometimes referred to as summer or summer-weight or lightweight oil that is made for use in the non-dormant season.

For reference purposes, in the link below there is a photo of what magnolia scale generally looks like.

Magnolia and Tuliptree Scale

Thanks!