[Problems and eradication of Ambrosia artemisiifolia L. in Quebec in the urban and suburban environments].
Ambrosia artemisiifolia is a common weed in Canada and it is one of the most important source of aero-allergenic pollen in the north-eastern part of North America. It is a problem mostly along roads in urban or suburban areas. It is easily controlled by herbicides but their use is increasingly restricted because of environmental considerations. Therefore, new methods must be developed to control this weed. Three types of controls were evaluated against Ambrosia artemisiifolia along an expressway in the summer of 1990. The control methods were hand weeding, mowing at 2 cm, 5 cm, or 8 cm, and crushing by a roadroller. These treatments were done at different dates in the course of the summer. Hand weeding was the most effective in reducing pollen and seed production although it was also the most expensive. Mowing was very effective when it was done at a height of 2 cm from the soil. It is the only height at which seed production was significantly reduced. Mowing efficacy in reducing pollen production tended to decrease with the raising of the mowing blade. The efficiency of weed pulling or moving improved when they were performed later in the growing season. Crushing was not an effective method of control. Mowing or hand weeding cannot eradicate Ambrosia artemisiifolia but if they are consistently used, they could reduce its population level over several years by decreasing seed production. The treatments either eliminated pollen production or reduced it at least by 88%, thereby insuring a relative relief for people allergic to the pollen of this plant.