THE BIOLOGY OF CANADIAN WEEDS.: 91. Malva pusilla Sm. (= M. rotundifolia L.)

This account provides information on the biology of round-leaved mallow, Malva pusilla Sm. (= M. rotundifolia L.). Primarily a weed of gardens and waste places, it has recently become troublesome in field crops causing yield losses of up to 90% in flax and lentil and up to 30% in wheat. Introduced from Eurasia, it is common mainly in the prairie provinces. Although often confused with two other weedy mallows, M. neglecta Wallr. and M. parviflora L., it has a different geographical distribution and can easily be distinguished by its short petals with bearded claws. Malva pusilla propagates by seed which are impermeable to water, exhibiting low germination unless scarified, and therefore capable of remaining dormant for long periods. Plant growth form varies greatly with competition. Round-leaved mallow is difficult to control chemically, but it can be effectively controlled with a fungus which is being developed as a commercial bioherbicide.