PERENNIAL WEED POPULATIONS AFTER 14 YEARS OF VARIABLE TILLAGE AND CROPPING PRACTICES

Management of perennial weeds is a major concern in reduced-tillage cr opping systems. Field research was conducted at Nashua, IA, from 1977 through 1990 to evaluate the long-term impacts of tillage and cropping patterns on perennial weed populations in corn and soybean production . Continuous corn and a corn/soybean rotation were conducted utilizing moldboard plow, chisel plow, ridge tillage, and no-tillage systems. T he research area was free of established perennial weed species at the initiation of the experiment in 1977. Hemp dogbane was observed by 19 81), with the greatest densities in no-tillage. By 1990, continuous co rn had greater hemp dogbane densities with no-tillage than other tilla ge system by crop rotation treatments. American germander densities we re not affected by tillage systems in 1980 and 1981, but by 1990, corn /soybean rotations had greater densities in moldboard plow than other tillage systems. Field bindweed developed primarily in the corn/soybea n rotations with the greatest densities occurring in no-tillage. Great er and more diverse populations of perennial weeds developed in reduce d-tillage systems than in the moldboard plow system. However, practice s used to control annual weeds and environmental factors interacted wi th tillage to regulate perennial weed populations.