Keys to Identification:

• Strong odor

• Leaves resemble fennel

This information courtesy of the Colorado Natural Areas Program

Family: Asteraceae (Sunflower)

Other Names: dog fennel, mayweed, stinking chamomile, stinkweed

USDA Code: ANCO2

Legal Status: Colorado Noxious Weed List B

IDENTIFICATION

Lifecycle: Annual

Growth form: forb

Flower: Flowers are solitary and borne at the ends of branches. Flowers are 0.75-1.25 inches in diameter, with 12 white ray flowers and a yellow disk center. White ray flowers have 3 distinct teeth.

Seeds/Fruit: Single-seeded fruit (achene) with about 10 ribs, approximately 1mm long (Stubbendieck et al. 1995).

Leaves: Leaves are alternate, highly divided into narrow segments, 2-6 cm long.

Stems: Mature plants are from 0.5 to 2 feet tall, highly branched, and have a foul odor. Lower portion often turns a maroon color as the stem ages.

Roots: Taproot with secondary fibrous root system.

Other: Foliage has an unpleasant odor.

Exotics: Matricaria perforata (scentless false mayweed) is locally common on the western slope, and is sometimes confused with Anthemis cotula (mayweed chamomile). In fact, most populations in the Gunnison basin and Blue River area which have been reported as A. cotula are probably M. perforata. A. cotula is distinguished by the presence of soft chaff (dry membranous bracts or scales) on the receptacle, and has odorous foliage. M. perforata lacks recepticular chaff. Corn chamomile (Anthemis arvensis) is almost identical to mayweed chamomile but can be identified by its lack of odor.

Natives: The native Hymenopappus newberryi has few stem leaves, and is perennial.

Agricultural: Contact with mayweed chamomile can cause skin rashes, blistering of livestock muzzles, and irritation to mucous membranes of grazing livestock (Whitson et al.1996). It may also impart a strong flavor to the milk of dairy animals (Whitson et al. 1996).

Ecological: Mayweed chamomile invades disturbed and overgrazed areas.

General requirements: Mayweed chamomile easily adapts to many different environments and growing conditions. It is commonly found in waste areas, fields, and overgrazed pastures.

Distribution: Found throughout the United States.

Life cycle: Mayweed chamomile germinates readily in the spring and fall. It has a dense, fibrous root system, which spreads rapidly during wet periods. Late summer and fall-germinated seedlings may overwinter as a rosette. In the spring, bolting commences with the elongation of the central stem. Overwintering plants flower in mid-May and spring germinated seedlings flower in June. Flowering stops after a killing frost.

Mode of reproduction: Mayweed chamomile reproduces by seed.

Seed production: Mayweed chamomile is a prolific seed producer and can produce up to 960,000 seeds per plant.

Seed bank: Seed may remain viable in the soil for 4-6 years.

Prevent the establishment of new infestations by minimizing disturbance and seed dispersal. Eliminate seed production to decrease the spread of this annual forb, and continue to deplete the seed bank for four to six years. Reseeding areas with perennial grasses for several years will reduce an infestation.

 

Colorado Natural Areas Program.  2000.  Creating an Integrated Weed Management Plan: A Handbook for Owners and Managers of Lands with Natural Values.  Colorado Natural Areas Program, Colorado State Parks, Colorado Department of Natural Resources; and Division of Plant Industry, Colorado Department of Agriculture.  Denver, Colorado. 349 pages.

 

Stubbendieck, J., G.Y. Friisoe and M.R. Bolick. 1995. Mayweed. Weeds of Nebraska and the Great Plains. Nebraska Department of Agriculture, Bureau of Plant Industry, Lincoln, Nebraska. pg. 75.

 

USDA, NRCS. 2005. The PLANTS Database, Version 3.5 (http://plants.usda.gov). Data compiled from various sources by Mark W. Skinner. National Plant Data Center, Baton Rouge, LA 70874-4490 USA

 

Virginia Tech University. (n.d.) Mayweed Chamomile: Anthemis cotula. Retrieved 11/04/2005 http://www.ppws.vt.edu/scott/weed_id/antco.htm

 

Whitson, T.D.(ed.), L.C. Burrill, S.A. Dewey, D.W. Cudney, B.E. Nelson, R.D. Lee, R. Parker. 1996. Mayweed chamomile. Weeds of the West. Western Society of Weed Science, in cooperation with the Western United States Land Grant Universities Cooperative Extension Services, Newark CA. pg. 54.