Look closely at the two pictures on this page of fall flowering plants. Both generally bloom at the same time and are pollinated by bees and other insects but only one of them has pollen small and fine enough to become airborne and cause suffering in a large percentage of the human population every fall. If you are one of these allergy sufferers, it is important to know what plant to blame so that you don't inadvertently try to eradicate the wrong one.
Many years ago I helped load a high school band trailer during football (allergy) season and was surprised to find a huge stand of a taller relative of the allergen inducing plant pictured in this blog growing along the fence just outside the band hall and next to where the trailer was loaded and unloaded. While its pollen would travel great distances on the wind, adults and student allergy sufferers did not need to be assaulted at close range and benefited from its removal.
You might even know the name of the plant culprit I speak of, ragweed, without knowing what ragweed looks like. One of these pictures is of flowering common ragweed. It is a perennial that spreads by underground roots in addition to setting seed. When I tell you the name of the other flowering plant it should be obvious which is which.
The other plant shown is goldenrod. It has showy flowers that echo its name. It is an important food source for bees and butterflies and is the plant you are likely to see growing by the roadsides during fall allergy season. However it is the nondescript ragweed plant that likely does not get your attention that is the reason for all of the watery eyes, runny noses and sneezing of the season.