A Multi-Tactic Approach to Manage Weed Population Dynamics in Crop Rotations

L.) are now grown with winter wheat and fallow. Integrating crop diversity with other cultural tactics enabled No-till systems have enabled producers to change crop rotations in producers to effectively control weeds with 50% less the semiarid Central Great Plains. Previously, winter wheat (Triticum aestivum L.)–fallow was the prevalent rotation; now producers grow herbicide inputs compared with their initial experiences warm-season crops along with winter wheat and fallow. Initially, weed with no-till rotations (Anderson, 2003). The cultural management was difficult in no-till rotations. However, an ecological approach reduced weed community density in their fields, approach to weed management, which integrates knowledge of weed thus minimizing the need for herbicides to control weeds. population dynamics with cultural tactics and long-term planning, has Pedigo (1995) suggested that scientists develop conenabled producers to control weeds with 50% less herbicides. This ceptual models to guide development of multi-tactic article explains the cultural tactics and ecological reasoning that led programs. In this article, we explain the cultural tactics to this successful approach; our goal is to provide insight and ideas and ecological reasoning that led to this approach with for other scientists and producers to plan multi-tactic weed manageweed management in the Central Great Plains; this exment. The ecological approach emphasizes three goals related to weed ample may provide insight and ideas for producers and population dynamics: enhancing natural loss of weed seeds in soil, reducing weed seedling establishment, and minimizing seed producscientists elsewhere to develop similar programs. Even tion by established plants. Cultural tactics used in this approach can though crop choices and cultural tactics may vary in be grouped into five categories: rotation design, crop sequencing, noother regions, a systematic approach to integrating tactill, crop residue management, and competitive crop canopies. Success tics that disrupt weed population growth may lead to of the approach requires cultural tactics in each category. successful weed management that is less dependent on herbicides. P in the semiarid Great Plains are searching DESIGN OF ECOLOGICALLY BASED for a broader approach to weed management than WEED MANAGEMENT relying primarily on herbicides. Several factors are stimulating this change in perspective. Herbicide-resistant In the Central Great Plains, annual weeds are the prevalent species infesting grain crops. Prominent weeds inweeds are now common (Lyon et al., 1996; Heap, 2005), forcing producers to use more expensive management clude downy brome (Bromus tectorum L.), jointed goatgrass (Aegilops cylindrica Host), kochia [Kochia scoparia tactics. A second factor is that some crops grown in the Great Plains, such as proso millet (Panicum miliaceum (L.) Schrad.], Russian thistle (Salsola iberica Sennen & Pau), green foxtail [Setaria viridis (L.) Beauv.], field sandL.) or forages, have few herbicides available for weed control. Thus, producers are seeking alternative tactics bur [Cenchrus longispinus (Hack.) Fern.], and redroot pigweed (Amaranthus retroflexus L.). With annual weeds, to supplement herbicides for weed management. Pedigo (1995), reviewing the progress of integrated pest the seed is the key component of population dynamics. The ecologically based approach emphasizes cultural management (IPM), found that IPM still emphasizes single-tactic, pesticide-based programs. To encourage a tactics that enhance natural loss of weed seeds in soil, reduce weed seedling establishment, and minimize seed broader approach to IPM, he suggested that scientists and producers consider a dualistic approach of prevenproduction by individual plants. Cultural tactics can be grouped into five categories: rotation design, crop setion and control, with an emphasis on multi-tactic management. Prevention seeks to reduce overall density of quencing, no-till, crop residue management, and competitive crop canopies (Fig. 1). In the following text, we pests and improve tolerance of crops to pest injury with cultural tactics. Mortensen et al. (2000), agreeing with describe tactics used for each category and explain the ecological basis for their impact on weed dynamics. Pedigo’s suggestion for multi-tactic management, further encouraged scientists to integrate weed management with cropping system design. Rotation Design: Sequencing of Cool-Season Crop rotations are changing in the Central Great Plains and Warm-Season Crops because of crop residue management and improved water Rotating cooland warm-season crops can reduce weed relations (Farahani et al., 1998). Warm-season crops such community density (Streibig, 1979; Thomas and Frick, as corn (Zea mays L.), proso millet, sorghum [Sorghum 1993). Different planting and harvest dates among these bicolor (L.) Moench], and sunflower (Helianthus annuus crops provide opportunities for producers to prevent either plant establishment or seed production by weeds. USDA-ARS, 2923 Medary Ave., Brookings, SD 57006. Received 29 For example, green foxtail emerges between mid-May June 2005. *Corresponding author ([email protected]). and early July, then begins flowering in early August. Winter wheat is harvested in early July; thus, producers Published in Agron. J. 97:1579–1583 (2005). Forum can easily control green foxtail before it flowers and doi:10.2134/agronj2005.0194 © American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: IPM, integrated pest management. 1579 Published online November 17, 2005