Hi! 
we are newer to the area and learning all about the impact of moisture and fungus with our plants. We have several holly that were impacted (and treated), but I’m worried that our new magnolias may have a fungus as well. 
The trees were planted in winter, and currently have a large amount of flowers on the verge of blooming - definitely some new growth - but I’m noticing leaves are yellowing with brown spots, and when I move them they easily fall off the tree.

I’m told this is the time of year magnolia will lose their leaves - but is it ALL leaves? I feel like they are thinning out quite a bit. I’m happy to see all of the new growth though. We have other pants around them that had to be treated for fungus (yellow anise) that are doing ok. We are just trying to keep it under control...all of this is new to us. 
I do suspect it may be a water issue as it’s recently warmed and our irrigation has been upended due to pool construction. 

Any advice is appreciated!