Weed of the Month

Learn about noxious weeds and steps you can take to manage or eradicate.  Each month we will bring you a new profile and helpful resources.

October Weed Profile


Colorado has three species of invasive chamomile; Corn, Mayweed, and Scentless. Mayweed and Scentless are List B noxious weeds.

Generally, the invasive chamomiles have white daisy-like flowers that grow at the end of branched stems. The leaves are alternate, 1-3 times pinnately divided. All are annual but Scentless may sometimes also be a short-lived perennial. All are natives of Europe/Eurasia. They can be found along roadsides, in fields, in disturbed areas, and cropland.

The leaves of Mayweed chamomile leaves are similar to corn chamomile but are more oblong and not as hairy. Mayweed chamomile’s stems are ridged and sometimes reddish. Mayweed chamomile, also known as dog fennel, has a very unpleasant smell. Corn chamomile is very limited in Colorado.

Scentless chamomile is the more common of the three. It has thread-like leaves. The single stems branch about halfway up and the flowers tend to be all at the same height, forming a flattish inflorescence.

For comparison of the floristic features for the three species, please refer to this chart


Flora of North America

Wikimedia Commons – Corn Chamomile

Invasive.org – Mayweed Chamomile

Invasive Species Compendium – Mayweed Chamomile

Manitoba – Scentless Chamomile

TechLine – Scentless Chamomile

USDA Weed Risk Assessment – Scentless chamomile

WASHINGTON STATE Noxious Weed Control Board – Scentless Chamomile

Items of Interest

Weed of the Month


January Weed Profile – Dalmatian Toadflax

February Weed Profile – Common Mulllein

March Weed Profile – Mediterranean Sage

April Weed Profile – Saltcedar

May Weed Profile – Absinth Wormwood 

June Weed Profile – Eurasian watermilfoil 

July Weed Profile – Yellow starthistle 

August Weed Profile – Hairy willowherb

September Weed Profile – Yellow toadflax


January Weed Profile – Cheatgrass

February Weed Profile – Myrtle Spurge

March Weed Profile – Hoary Cress

April Weed Profile – Leafy Spurge

May Weed Profile – Scotch Thistle

June Weed Profile – Dyer’s Woad

July Weed Profile – Orange Hawkweed

August Weed Profile – Purple Loosestrife

September Weed Profile – Teasel

October Weed Profile – Canada Thistle

November Weed Profile – Russian Knapweed

December Weed Profile – Russian Olive