Where you’ll see it

: Fields, riverbanks, roadsides, rural areas



There’s a ton in: the Midwest, the Mississippi River basin



Peak time: Summer and fall



“The most allergenic plant we have is ragweed,” says Dr. Filley, “It is less common on the West Coast or in New England. Therefore there is less pollen in those areas.” About 75% of Americans who have plant allergies are sensitive to ragweed, according to the Asthma and Allergy Foundation of America.