Origin:
Native to the eastern United States, and still most common there, but found throughout North America.
Biology:
A summer annual weed with reproduction from seed. Germination is very early in the spring when soil temperatures are still very low, and when soil temperatures go above about 86 degrees germination stops. The pollen from this plant is a very common cause of hay fever symptoms.
Identification:
Mature plants are erect and well branched off of the primary stem, and stems are covered with long, rough hairs. The leaves may be hairy or nearly smooth and they are generally egg-shaped and pointed at the tip. This shape is hard to see due to the division of the leaf into leaflets, and often these leaflets further deeply lobed, a condition called “pinnatifid”, or twice compound. The lower leaves are stalked while upper leaves may not be. The flowers are tiny and inconspicuous, but they occur in long, dense clusters on the terminal branches, and these may be over 6 inches long. Each flower will contain only a single seed, but they produce large amounts of wind-blown pollen.
Characteristicts Important to Control:
This weed prefers heavy, moist soils, but is a problem in just about any situation, including landscape, crops, roadsides, empty lots, or ditch banks. It does not tolerate close mowing and generally is not a weed found in maintained turf. Physical removal is possible as the roots are shallow and fibrous.
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