Family: Composite, Asteraceae.
Habitat: Thin turf, agronomic crops, pastures, orchards, fallow fields, waste areas, and roadsides.
Life cycle: Summer or winter annual.
Growth habit: Seedlings develop a basal rosette and mature plants erect are reaching 6 1/2 ft in height.
Leaves: The mature plant has leaves that are entirely without petioles (sessile). Leaves are 4 inches long, 10 mm wide, alternate, linear, entire or more often toothed, crowded along the stem, and hairy. Leaves become progressively smaller up the stem.
Stem: Erect, solid, hairy, reaching 6 1/2 ft in height.
Flower: Many small inconspicuous flower heads occur at the top of the central stem. Individual flowers are 5 mm in diameter with white or slightly pink ray flowers and yellow disk flowers.
Roots: A short taproot with a secondary fibrous root system.
Similar Plants: In the rosette stage of growth, horseweed might resemble other weeds that have this rosette habit, such as Shepherd’s-Purse or Virginia Pepperweed.
The Problem is……………Marestail, also called horseweed, has continuous germination, is highly competitive, fast moving and wide spreading with wind dispersal. Many plants are also Glyphosate tolerant, and some populations have ALS and PPO-inhibitor resistance.
Currently there are 21 weeds on the Ohio Prohibited Noxious Weed List:
- Shattercane (Sorghum bicolor) – February 8
- Russian thistle (Salsola Kali var. tenuifolia) – February 22
- Johnsongrass (Sorghum halepense L. (Pers.)) May 24
- Wild parsnip (Pastinaca sativa) – May 21
- Wild carrot (Queen Anne’s lace) (Daucus carota L.) – June 5
- Oxeye daisy (Chrysanthermum leucanthemum var. pinnatifidum) – May 3
- Wild mustard (Brassica kaber var. pinnatifida) – June 12
- Grapevines: when growing in groups of one hundred or more and not pruned, sprayed,cultivated, or otherwise maintained for two consecutive years. – February 15
- Canada thistle (Cirsium arvense L. (Scop.)) – March 29
- Poison hemlock (Conium maculatum) – May 31
- Cressleaf groundsel (Senecio glabellus) – June 21
- Musk thistle (Carduus nutans) – March 26
- Purple loosestrife (Lythrum salicaria) – April 17
- Mile-A-Minute Weed (Polygonum perfoliatum) – March 7
- Giant Hogweed (Heracleum mantegazzianum) – March 14
- Apple of Peru (Nicandra physalodes) – February 28
- Marestail (Conyza canadensis) – July 5
- Kochia (Bassia scoparia) – May 1
- Palmer amaranth (Amaranthus palmeri)
- Kudzu (Pueraria montana var. lobata) – April 11
- Japanese Knotweed (Polygonum cuspidatum) – April 2
Each week, for the next 21 weeks, I will post information and pictures on how to identify these invasive and harmful plants.