THE BIOLOGY OF CANADIAN WEEDS .99. MATRICARIA-PERFORATA MERAT (ASTERACEAE)

Scentless chamomile, Matricaria perforata Merat, (= M. maritima var. agrestis (Knaf) Wilmott), is an introduced weed having an annual to short-lived perennial life cycle. Two cytotype races are found in Canada with a distinctive geographic distribution. The tetraploid (2n = 36) is abundant in agricultural habitats of the Prairie region, whereas the diploid (2n = 18) is found mainly in ruderal habitats of the Atlantic region. Infestations are found in many annual and perennial crops, pastures, wasteland, lawns, gardens, roadsides, fence lines, and ditches. The plant reproduces entirely by seed, producing up to 1.8 million seeds m-2 in dense monospecific stands. A density of 25 annual plants m-2 can result in a 55% reduction in spring wheat yield under cool wet conditions. Shallow preseeding tillage in late autumn or early spring is an effective method of cultural control. Several herbicides are recommended for control of the weed in crop and noncrop areas. Scenttess chamomile is considered a suitable candidate for biological control.