(Washington, Oregon, California)

In the Pacific region, trees usually pollinate from February to June. The trees that cause the most allergy-related problems in this region are the cedar, walnut and rye. Other trees that may cause allergies in this region are the hazel, juniper, alder, ash, birch, box elder and oak.

Grasses generally pollinate from March to November in this region. Some of the most common allergy-causing grasses are sweet vernal, fescue, bluegrass, Bermuda grass, brome, orchard, quack grass, wheat grass and redtop.

The weed season for the region generally lasts from April to November, including ragweed, chenopod and sage. Other weeds that can cause allergy problems include pigweed, iodine bush, saltbush, lamb's-quarter, Mexican fire bush and Russian thistle.