We live in toronto in the beaches area (sandy soil) and this maple has mix of sun and shade.. not too sunny! All of a sudden it looks like this. What can I do? Any help is appreciated! Thank you!
This summer has been so difficult for small trees to maintain their healthy status. Your Acer palmatum has suffered dangerous conditions especially. Even with some shade, a few days with scorching sun, no rain, and sandy soil with too easy drainage has cost you the enjoyment of a sweet dwarf specimen. Japanese maples love lots of water, and yours got very little in a short time of hot drought.
Trim off as much of the dead foliage as possible, water around the root area frequently, and consider topping the ground all the way to the edge of the canopy with mulch material to maintain the soil surface moist. When the tree recovers, you may add compost to the surface area to help offset the sandy conditions a little.
To read more on the topic that matches your situation, view the blog by Davey tree expert.
Also, you may wish to learn more about leaf scorch at http://rhs.org.uk