Effects of weed management systems on canopy-inhabiting and surface-active arthropods in Iowa soybeans

Pest management strategies involving weed suppression in agroecosystems have changed considerably in the last few years. With advances in biotechnology, soybean varieties have been developed that are resistant to some broad-spectrum herbicides. Studies were conducted from 1996 through 1998 to better understand the effects of these new varieties and their weed management systems on arthropods and to assess the economics of adopting these systems;The effects of transgenic herbicide-resistant soybean varieties and their corresponding weed management strategies on canopy insects were examined in studies at two locations in Iowa from 1997 to 1998. Usually, weed management systems that allow more weed escapes also have larger insect population densities. However, systems with fewer weeds seemingly were preferred by potato leafhoppers. Bean leaf beetles and potato leathoppers showed preferences for certain varieties, but this was attributed to soybean plant height;Surface-active arthropods were examined using pitfall traps in an Iowa soybean field from 1996 through 1998. A total of 75,078 arthropods were identified from 4,800 pitfall traps. Ground beetles comprised the majority of arthropods captured (46%) with field crickets being the second most numerous (40%). However, when comparing conventional weed management and hand weeding systems, more predators were found in the hand weeded system, with the exception of the ground beetle Scarites. Finding more predators in plots with less weeds is attributed to food preference and availability. Inconsistent results in populations densities of Phalangidae indicate that pitfall trapping may not be an adequate method for assessing phalangid populations in soybean fields;The economics of adopting these new weed management systems was evaluated by partial budgeting analysis of the different varietal yields and input costs associated with them. Yield differences were observed when comparing varieties and weed management. These data indicated that a conventional soybean variety with a conventional weed management system can yield as well and have a similar return on yield as a transgenic variety with a targeted weed management system;More than 75,000 Collembola were collected in pitfall traps from 1996 through 1998. Collembola population densities were lower in the hand weeded system compared to the other two systems. These results are attributed to more weeds and less soil disturbance occurring in the targeted and conventional systems;In general, we found that while the new soybean varieties did not seemingly have an affect on arthropods, the weed management systems did. In addition, adoption of these new weed management systems were found to be economically beneficial only when weed conditions are such that multiple conventional herbicide applications and/or cultivations are necessary