Answer:

ragweeds

Answer	Crossword Clue
RAGWEEDS	Common pollen producers
RAGWEEDS	Sneezing causes
RAGWEEDS	Hay fever causes

RAGWEEDS	Nature's nose annoyers
RAGWEEDS	What botanists call "Ambrosia"
RAGWEEDS	These make thousands sneeze.
RAGWEEDS	Pollen carriers
RAGWEEDS	Plants hated by hay-fever sufferers
RAGWEEDS	Troublesome plants
RAGWEEDS	Sneeze causers, for some