Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2007
Publication Date: 9/10/2007
Citation: Davis, A.S., Williams, M. 2007. Variation in wild proso millet fecundity in sweet corn has residual effects in snap bean. Weed Science. 55(5):502-507. Interpretive Summary: Does one year's seeding really require seven year's weeding? Farmer wisdom suggests that weeds going to seed in one year can cause weed management problems in following growing seasons, but this intuitive notion has received few tests. We conducted field experiments in 2005 and 2006 to determine whether different levels of wild proso millet (WPM) seed production in a sweet corn crop would affect WPM seedling numbers, success of weed management, and crop yield in a following snap bean crop. Although weed management outcomes in snap bean were little affected by variation in WPM seed production the previous season, the number of WPM seedlings in snap bean was greater and snap bean yield was lower in those plots where more WPM seeds fell. The relationship between number of WPM seedlings and snap bean yield was indirect, mediated through reduced snap bean survival to maturity in plots where there were more WPM seedlings. Fewer mature snap bean plants translated into less yield. This research demonstrates the need for better techniques to reduce weed seed inputs to the soil seedbank and to control early-season weeds, especially in those production systems in which preemergence herbicides are not an option.
Technical Abstract: Bioeconomic models are predicated upon the relationship between weed fecundity and crop yield loss in consecutive growing seasons, yet this phenomenon has received few empirical tests. Residual effects of wild proso millet (Panicum miliaceum; WPM) fecundity in sweet corn upon WPM seedling recruitment, weed management efficacy and crop yield within a subsequent snap bean crop were investigated with field experiments in Urbana, IL, in 2005 and 2006. Wild proso millet fecundity in sweet corn showed strong positive associations with WPM seedbank density, seedling recruitment and demographic transitions within snap bean. A negative exponential relationship between wild proso millet initial seedling density and seedling survival of a single rotary hoe pass indicated that the rotary hoe was ineffective at low weed population densities, but its efficacy increased with increasing weed population density to a maximum of 75% seedling mortality. Efficacy of postemergent chemical control of WPM was unaffected by WPM population density. Path analysis models demonstrated dependence between WPM fecundity in sweet corn, WPM seedling recruitment in snap bean and reductions in snap bean yield in subsequent growing season, mediated by negative impacts of WPM seedling establishment on snap bean stand. These results underscore the importance of expanding integrated weed management programs to include management of annual weed populations both at the end of their life cycle, by reducing fecundity and seed survival, and at the very beginning of their life cycle, by reducing seedling recruitment and establishment.