From Durham County:
"It actually is worse here than anywhere else," he said. "Nothing dies here, the weather's too good."
In the spring, Dr. Lugar said the biggest allergens are tree pollens, like elm, maple and oak. Unlike pine pollen, which is visible in the trees and in the yellow film it leaves on cars and windows, the most problematic allergens are too small to see.
"And tree pollen, for example, can travel for miles. So even if you assume that you are surrounded by concrete buildings, the pollen that's been produced miles away will reach your nose."
Mnemonic for the pollen calendar: TGR MI
Tree pollen - spring
Grass pollen - summer
Ragweed and weeds - fall
Indoor allergens are year-round
Pollen-producing plants (weeds and trees) in Omaha, Nebraska. V. Dimov, M.D.
Seasonal Allergies Last Longer In The South. Durham County Story, 2009.
Pollen Role in Allergy and Asthma
Image source: Southern United States, Wikipedia, GNU Free Documentation License.