Demography of Abutilon theoprasti and Setaria faberi in three crop rotation systems

Field experiments were conducted to characterize the demography of Abutilon theophrasti and Setaria faberi in a conventionally managed 2-year (maize/soya bean) rotation, and in 3-year (maize/soya bean/triticale + red clover) and 4-year (maize/soya bean/triticale + lucerne/lucerne) rotations managed with 72% and 79% lower herbicide inputs respectively. Rates of weed seedling recruitment, seedling survival and adult plant fecundity were determined for populations in each phase of each rotation and used to calculate annual rates of weed population change, Delta. In both years of the study, Delta for A. theophrasti populations declined or remained stable in all three rotation systems. Despite greater rates of seedling survival and fecundity in maize and soya bean in the 3- and 4-year rotations, increases in Delta for A. theophrasti populations were prevented in these systems because of low fecundity in triticale and low seedling survival and fecundity in lucerne. For Setaria faberi populations, Delta remained stable in the 2-year rotation, increased in the 3-year rotation in both years, and increased in the 4-year rotation in 1 year. The results of this study indicate that when herbicide use is reduced, rotations that include triticale and lucerne can facilitate the suppression of A. theophrasti. Rotations that include lucerne can contribute to restraining S. faberi population growth, given adequate levels of seedling mortality in this crop.