What is the definition or description of: pigweed allergy?

Fall weed: Pigweed is a type of weed that usually pollinates in the fall in most areas of the USA. Inhalation of pigweed pollen, when allergic, can cause nasal and eye allergy symptoms like runny nose, itchy nose, itchy watery eyes, and sometimes cough or breathing difficulty if allergy is severe enough.

Allergy to pollen: Pigweed, a name used for a variety of Amaranth plants that release pollen in the fall. People who are allergic to pigweed pollen can develop a runny nose, itchy eyes, and other allergy symptoms. Most pigweed is herbicide resistant. To combat this, farmers use higher dose herbicides and 'restricted herbicides' to kill pigweed. There is concern that pigweed pollen may carry herbicide residue.