The mature plant can reach almost 4 feet (1.2 m) tall. It is well branched. Leaves are gray green and are covered with both short, stiff and long, soft hairs. Leaves are alternate to one another along the stem. Leaf edges range from smooth to weakly toothed or lobed. Upper leaves are linear to lance shaped. Lower leaves are generally egg shaped and taper to a short stalk.
Flowers bloom from June through September. Upper branches contain many flowering stalks and there is one flower head per stalk. The flower head has a green, cup-shaped base formed by green leaflike structures (bracts) that overlap. The base tapers toward the top and encloses tiny, yellow flowers (disk flowers) that are surrounded by small, cream-colored bristles. As the fruit develop the head opens up and the bristles loosen.
Hairy fleabane is a summer annual plant that can emerge from October through March. This plant can withstand several mowings and still produce seed. Shallow cultivation when weeds are in the seedling stage provides effective control. Postemergence herbicides, can control this species when it is small (less than 18-21 leaves), but once plants bolt (sending up flowering stalks), they will not control it. Plants larger than 21 leaves may not be adequately controlled. Glyphosate provides excellent control when these weeds are small. Be careful to follow all label instructions. Plants of a close relative, horseweed, have developed resistance to glyphosate in many parts of the Unites States, including California. Thus, it is critical to monitor control efforts and follow up with hand hoeing to prevent escape of any plants that might be resistant. Preemergence herbicides may provide adequate control.
In other words, this is a difficult weed to control. Possible control methods include, preemergence herbicide, postemergence herbicide when the plant is small, hand pulling, hoeing, and mowing. Do not let this plant go to seed. Please follow all directions when handling herbicides.
For more information go to; ipm.ucanr.edu ■