When the leaves on my sycamore tree went from green to brown in about two weeks, I took samples to my local nursery and was told the tree was getting too much water. I noticed a couple of other sycamore trees in the neighborhood with the same problem. I think the tree is dead and want to replace it, but I want to make sure before I dig it out. Dieback of branches and foliage is common when trees are watered the same as the surrounding lawn.
Trees prefer deep and infrequent watering.
The visual symptoms can appear suddenly, even though your tree could have been under stress for the past two years. If the tree is not too severely damaged, correcting the irrigation situation should stimulate healthy new growth. Anthracnose is a disease that attacks many plants, but seems most prevalent on Platanus, sycamore trees. Fortunately, anthracnose rarely causes permanent damage in California, except to elm trees. A fungus affecting developing shoots and expanding leaves causes anthracnose.