Effect of repetitive mowing on common ragweed (Ambrosia artemisiifolia L.) pollen and seed production.

Agriculture and Agri-Food Canada (AAFC), Soils and Crops Research and Development Centre, Quebec, QC, Canada G1V 2J3. marie-josee.simard@agr.gc.ca.
Ann Agric Environ Med 2011;18(1):55–62
Ambrosia artemisiifolia L (common ragweed) is a familiar roadside weed in southern Quebec (Canada) that produces large amounts of airborne pollen responsible for multiple rhino-conjunctivitis (hay fever) cases. As roadside weeds are increasingly controlled by mowing alone, the effect of a mowing treatment on pollen production was evaluated. Ambrosia artemisiifolia plants were grown in a greenhouse at 4 densities (1, 3, 6 and 12 plants per 314 cm(2) pot) and either left intact or mowed (10 cm from the ground) when the plants reached 25 cm in height, i.e. twice during the life cycle of this annual plant. Pollen production per male inflorescence was collected in open-top bags and counted. Inflorescence mass, length, location on the plant and date of anthesis onset was noted. Above-ground plant biomass and seed production was also evaluated. Mowed plants produced less pollen per unit of inflorescence length than intact plants. Pollen production per plant was reduced by a factor of 8.84 by the double mowing treatment, while viable seed production per plant was reduced by a factor of 4.66, irrespective of density. Mowing twice has the potential to reduce airborne pollen loads but Ambrosia artemisiifolia seed banks are unikely to be depleted by this management strategy.