Submitted to: Western Society of Weed Science Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2007
Publication Date: 7/21/2008
Citation: Peachey, E., Greco, A., Green, J., Boydston, R.A. 2008. Activity, Density, and Weed Seed Predation Potential of Ground Beetles in Annual Row Crops of the Pacific Northwest. Western Society of Weed Science Meeting Proceedings. 61:9. 2008.
Technical Abstract: Regulation of weed seed banks in agricultural systems involves management of seed input from seed rain, and seed removal from mortality and germination. While seed rain, germination, and emergence are managed using a number of methods such as tillage and herbicides, management of seed mortality is frequently overlooked. Seed predation by invertebrates such as carabid beetles is a key source of mortality in many cropping systems. The influence of ground beetles on weed seed density in the soil, and the potential to increase the abundance of these seed predators in agricultural systems has not been determined in commercial vegetable production sites in the Pacific Northwest, and is poorly understood in many cropping systems. Objectives were to determine the impact of select agronomic practices on seed predator activity density and seed predation efficacy. Project objectives were addressed by measuring activity density of seed predator ground beetles and weed seed consumption rates in farm fields and research plots in the maritime Willamette Valley of Oregon and the high desert Columbia Basin region of Washington. Pterostichus melanarius and Harpalus pensylvanicus were the primary species of all fields in the Willamette Valley. Activity density (AD) tended to increase as summer progressed but inconsistently among sites. Mid-season insecticide treatments applied to plots in farm fields reduced seed predator activity density most at the center of the plot, but beetles slowly recolonized the insecticide treated areas. In the high desert Columbia Basin, species diversity was similar in both years. The primary species in both the organic (37% of total species in organic) and conventional fields (36% of total species in conventional) was Harpalus pensylvanicus. The second and third most prevalent species were Agonum melanarium (23% of organic and 27% of conventional) and Pterostichus melanarius (20% of organic and 12% of conventional), respectively. At the maritime research station site in Corvallis, the primary species trapped was P. melanarius and insecticide treatments reduced density of this species by 86%. No effects of spring tillage system were noted on AD. The rate of wild proso millet seed loss to ground beetle predation declined from 15% to 4% when insecticides were applied mid-season, and from 15% to 1% when insecticides were applied broadcast in conventional tillage.