Hi, two of my magnolias teddy bear are developing whole branches of brown leaves. They have been in the ground 2-3 years, the third one (far right) is quite healthy and has been in the ground for about one year. The two affected still show some healthy growth.
We’ve had a lot of rain and the soil is quite wet but not sopping wet.
I did a soil test and it came out neutral.
I’m feeding them occasionally with 



Eco-seaweed.
the mulch is cane mulch, not close to the trunk.
Please advise how to rescue them! Thank you.