Wichita, the largest city in the state, owes its worse than average pollen score to weeds and grasses, the usual culprit for common nasal allergies. As a result, medicines are used more often, moving Wichita one spot higher on the list. It was No. 7 last year. “Vegetation, including pollen producing weeds, grasses and trees, thrive on the increased CO2 and produce more robust pollen,” Dr. Borczuk says. Wichita is also the worst place for allergy sufferers in the Midwest.