Model of crop : weed competition applied to maize : Abutilon theophrasti interactions. II. Assessing the impact of climate: implications for economicthresholds

The practical application of single-season economic thresholds for post-eme rgence weed control decisions has been frustrated by the impact of growing season, climate and edaphic factors on crop:weed interactions. Competition in a mixed plant community is a dynamic process that is contingent upon spe cies-specific growth characteristics and their expression based on environm ental conditions. To address these issues, a modified version of the ALMANA C competition model was parameterized and run to simulate maize:Abutilon th eophrasti competition with 30 years (1966-95) of historical climate data fo r a site in New York State. Simulations indicate that, when weeds do not em erge before maize, maize will only suffer substantial yield reductions from A. theophrasti competition in two out of every 10 years at this site. It i s also evident that economic thresholds based solely on the level of weed i nfestation are inherently flawed. Long-term simulation results suggest that estimates of early season water stress could be used as an independent too l for rationalizing post-emergence control decisions. Shifting the focus fr om quantifying the infestation intensity of the weed population to assessin g the competitive status of the maize crop indirectly with climate informat ion may alleviate many of the problems commonly associated with threshold m anagement strategies.