Thursday, November 16, 2006 - 10:00 AM

Seasonal Patterns in Post-dispersal Weed Seed Predation in Three Cropping Systems.

Andrew H. Heggenstaller1, Fabian D. Menalled2, Matt Liebman1, and Paula R. Westerman3. (1) Iowa State Univ.-Dept. Agronomy, 3403 Agronomy Hall, Ames, IA 50011-1010, (2) Montana State Univ, 719 Leon Johnson Hall, Bozeman, MT 59717-3120, (3) Iowa State Univerity -Dept. Agron., 2501 Agronomy Hall, Ames, IA 50011

Seed predation may contribute to integrated weed management systems that reduce herbicide requirements for crop production. However, the extent to which cropping practices control rates of seed predation is not well established. To assess the influence of different crops and management systems on weed seed losses to predators, we repeatedly measured rates of removal of velvetleaf and giant foxtail seeds during 2003 and 2004 in a conventionally managed 2-yr rotation (corn-soybean), and in 3-yr (corn-soybean-triticale + red clover), and 4-yr (corn-soybean-triticale + alfalfa-alfalfa) rotations managed with reduced herbicide and fertilizer inputs. Predation of giant foxtail seeds was equal (8 sampling periods) or greater (19 sampling periods) than predation of velvetleaf seeds, but the influence of crops on predation losses was generally similar for the two weeds. Differences in seed predation among crops were found to be much greater than differences due to management systems applied to the same crop present in different rotations. Seasonal patterns in seed predation were crop-specific and complementary. In corn and soybean, seed predation was low in spring, high in summer and low in autumn. In triticale-legume intercrops, seed predation was high in spring, low in summer and moderate in autumn. In alfalfa hay, seed predation fluctuated from high to low, matching the periodic harvest and regrowth cycle of the crop. Measurements of crop canopy light interception taken in 2004 were positively correlated with rates of seed removal for both velvetleaf (r = 0.54; P < 0.001) and foxtail (r = 0.25; P < 0.001), suggesting that vegetative cover promotes weed seed predation. Diversified cropping systems that include a range of phenologically dissimilar crop species are likely to provide the greatest opportunities for the destruction of weed seeds by predators.