I planted a Jane Magnolia in the front yard of my row house about 2 or 3 years ago. I keep hoping it will do better, but every year it seems to be the same. It starts out good, with some blooms and then lots of leaves. Then the leaves seem to get some sort of powdery white looking stuff on them. I have sprayed for mold and aphids, which sometimes helps. Then the leaves turn yellow or spotty brown and they fall off, as if it's October. By mid-July, I don't think I'll have any leaves left (although I do still see new growth). I have no idea if I'm overwatering or underwatering. Some websites say to keep it moist and give plenty of water. Others say you hardly need to water at all. I think mine gets water every day. Even if I don't specifically water the tree, I have to water all of the other stuff in my small garden, so I think it gets a good amount of water. If I don't water my azaleas and rhododendrons and impatiens every day when the weather is hot, they wilt and droop, and stop growing. When I soak them every morning, they always look lush and green. I don't know how to do that without the Jane Magnolia getting some of that water. I don't want to give up on the Jane, but it looks terrible from mid-July through the fall every year. Any suggestions? Thanks in advance for the advice!
The powdery residue is from a fungal issue called powdery mildew. You can try treating the tree with neem oil, often sold as fruit tree spray in some places. Here is more information: https://www.gardeningknowhow.com/plant-problems/disease/get-the-cure-for-powdery-mildew.htm