Scentless chamomile, an escaped ornamental, is a bushy annual plant, ½ to two feet tall, with showy, twelve-petaled white flowers. It is nearly identical in appearance to the strong scented species (Mayweed chamomile, Anthemis cotula L.), but can be easily distinguished by its lack of odor. This member of the Sunflower family flowers from May to October. Imported from Europe as an ornamental, Scentless chamomile now grows worldwide. The plant has become established in Aspen,Breckenridge, Crested Butte and Vail as well as other mountainous regions in Colorado. Scentless chamomile has no forage value and can cause blistering of muzzles, irritation of mucous membranes, and skin rashes in livestock. Alternatives include Feverfew (Tanacetumparthenium), Cutleaf Daisy (Erigeron compositus) or native daisies.
For more info and how to control, check out the La Plata County weeds Dept. Fact Sheet
Don't confuse chamomile with Oxeye daisy, which has lobed broad leafs.
Chamomile has more fern like leaves. The below picture is Oxeye daisy.