Hello, that yellowing looks like normal leaf drop.  Right now, the emerald ash borer is only known from one location in Oregon near Forest Grove.  If it spreads it is likely that all Ash trees in Oregon will be threatened.  However, we don't really know what the actual status is yet.  Most the trees were destroyed to control the beetle at the site near Forest Grove.

It is possible to protect individual street and landscape trees with insecticides.  

Here is some information that may help;

Ash trees naturally can have some crown decline and it is not uncommon for our native Oregon ash, or the planted ash trees, to show crown issues like dead branches. You will want to examine the trees closely.

Learn about the emerald ash borer with this guide from Oregon Dept. of Forestry:

• ODF Factsheet

Correct identification and reporting will help state officials determine how far and how fast this insect is spreading in Oregon. Here are some resources to help with correct identification:

• EAB look-alikes guide from Oregon Department of Agriculture
• Oregon Forest Pest detector guide
• Oregon Department of Agriculture EAB webpage

If you feel confident you have EAB, please report sightings at the Oregon Invasive Species Council Hotline.

If you feel you want to protect these trees with insecticides, it is  best to contact an arborist or discuss with a nursery that sells these products.  Here is a guidebook but it is pretty detailed.  You may want to make sure your arborist reads it.

 http://www.emeraldashborer.info/documents/Multistate_EAB_Insecticide_Fact_Sheet.pdf

Finally, it may be too early to begin this type of treatment, as we don't know the whether the insect is spreading at this time.