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Weed Dynamics and Management Strategies for Cropping Systems in the Northern Great Plains

^a Agric. and Agri-Food Can., Box 1000A RR 3, Brandon, MB, Canada R7A 5Y3
^b USDA, Cent. Plains Res. Cent., Box 400, Akron, CO 80720
^c Agric. and Agri-Food Can., Box 3000, Lethbridge, AB, Canada T1J 4B1
^d Dep. of Land Resour. and Environ. Sci., Univ. of Montana, Bozeman, MT 59717-0312

View larger version (28K): [in a new window]   Fig. 1. Weed biomass (dry weight) of green foxtail and field sandbur in proso millet in five rotations, 8 yr after initiation of study at Akron, CO. Data are averaged across 2 yr. Bars with the same letter are not significantly different based on Fisher's LSD (0.05). Crop codes: W = winter wheat, M = millet, F = fallow, and C = corn.

View larger version (23K): [in a new window]   Fig. 2. Persistence of seed viability of downy brome and jointed goatgrass when seed remains within the top 2.5 cm of the soil (adapted from Donald and Zimdahl 1987 and Anderson, 1998a).

View larger version (24K): [in a new window]   Fig. 3. Average seedling density (± standard error) of all weed species in zero- and conventional tillage systems within six crop rotations at Indian Head, SK, from 1992–1996. Rotations (R) 1 through 3 were wheat–canola–wheat–lentil (Lens culinaris Medikus), where R1 (Conv 1) had conventional input levels with only postemergence herbicides, R2 (Conv 2) was similar but with pre-emergence trifluralin in canola and lentil, and R3 (Reduced Input 1) was similar to R2 but with reduced herbicide inputs (no grassy weed herbicides in wheat). Rotation 4 (Reduced Input 2) was also low input wheat–pea (Pisum sativum L.)–wheat–lentil with a similar reduced herbicide strategy as R3 and 50% reduced fertilizer usage in wheat. Rotation 5 (Diversified 1) was conventional input and diversified canaryseed (Phalaris canariensis L.)–sunflower–wheat–lentil, and R6 (Diversified 2) was conventional input diversified wheat–tame mustard–canaryseed–lentil.

View larger version (24K): [in a new window]   Fig. 4. Average fall seedbank density (± standard error) of all weed species in zero- and conventional tillage systems within six crop rotations at Indian Head, SK, from 1992–1996. Rotations (R) 1 through 3 were wheat–canola–wheat–lentil, where R1 (Conv 1) had conventional input levels with only postemergence herbicides, R2 (Conv 2) was similar but with pre-emergence trifluralin in canola and lentil, and R3 (Reduced Input 1) was similar to R2 but with reduced herbicide inputs (no grassy weed herbicides in wheat). Rotation 4 (Reduced Input 2) was also low input wheat–pea–wheat–lentil with a similar reduced herbicide strategy as R3 and 50% reduced fertilizer usage in wheat. Rotation 5 (Diversified 1) was conventional input and diversified canaryseed–sunflower–wheat–lentil, and R6 (Diversified 2) was conventional input diversified wheat–tame mustard–canaryseed–lentil.

View larger version (32K): [in a new window]   Fig. 5. Grain yield of corn in weed-free and weed-infested conditions, as affected by cultural practice combinations at Akron, CO. Conventional system was 37000 plants ha-1 at a row spacing of 76 cm, with N fertilizer broadcast at planting. Cultural practices were banding N by the seed (Cult. 1), increasing crop density to 47000 plants ha-1 (Cult. 2), and reducing row spacing to 38 cm (Cult. 3). Data are averaged across 2 yr. Bars with the same letter are not significantly different based on Fisher's LSD (0.05).