Annual ragweed can invade and suppress weak and overgrazed pastures, reducing productivity. Its pollen can cause hay fever and aggravate asthma.
Establishes each year, normally germinating from spring to summer. Germination can occur at other times of year in suitable conditions. Flowering is triggered by decreasing day length and occurs from mid-to late March, after which plants die. Late-germinating plants may overwinter before flowering the following autumn.