I live on a block with all new street trees approx 3 years old. They get regular water and annual compost and are generally well-cared for. A couple weeks back I noticed some of our neighbor's trees leaves were losing color. This weekend it spread to ours. Is this something to worry about? The leaf in the photo is after one or two days. The neighbor's trees are much more faded.

PHOTO: http://forums.gardenweb.com/forums/pests/msg0721122515116.jpg

The symptoms you describe and show could very well be iron chlorosis (yellowing of foliage). Iron chlorosis is often the result of planting pin oak, an acid soil-loving tree species, on high pH soils, thus rendering the micro-nutrient (but essential) iron unavailable for uptake. Iron chlorosis is not a disease (it is a nutrient defiency), thus cannot be spread from tree to tree.

Treatment options include adding iron or sulfur-based fertilizers to acidify the soil around the tree OR treating the foliage of the pin oak with foliar sprays containing ferrous sulfate or chelated iron. These products are available at most Home & Garden Stores (Lowes, Home Depot, Kmart, etc.).

If the tree is actually on the city's right-of-way, you may ask the city if they will treat the tree for you.