I purchased an acer palmatum orange dream about a month ago, and potted it into a new, bigger pot. Nothing major, no real disturbance of the root balls. The tree had some mild burn on the top leaves which the nursery suggested was from under watering.

I've been watering it twice a week (I live in Palo Alto, CA, so it's pretty dry), and the tree has now developed these white spots. Further, more of the leaves seem to be turning brown at the tip. I'd think it was just the onset of fall, but they're turning straight to brown, not yellow or orange. Picture below.

HELP!

http://www.flickr.com/photos/ewwr1842/6210217314/