Hi,

Although I can't be totally sure since I can't see where the tree is growing...my best guess is that part of it is growing in shade and part of it is growing in sun. I bet the green areas are in the shade and the red areas are in the sun.

Layne

Layne - Thanks for the try - the tree receives full sun almost all day and has a 'sister' growing 10 feet away that is in perfect condition. It's really a strange situation ! I will try to call the county ag extension and see what they say. Thanks again!

I'm not an expert but could it be reverting to it's rootstock? (Are Japanese Maples grafted or "own-root"?) I am having the same problem with my "carole mackie" daphne.
One side keeps growing stems with solid green leaves and the rest of the branches have the expected variegated leaves. It has been recommended by people here on the shrub forum that I continue to chop off the solid green branches as they occur or else the entire shrub will revert to solid green leaves. This might be a huge problem for you since it involves half of your tree.
.......Jan