Emergence pattern of Palmer amaranth (Amaranthus palmeri) influenced by tillage timings and residual herbicides
Abstract The evolution of multiple herbicide-resistant weeds, including Palmer amaranth, has necessitated the implementation of an integrated weed management (IWM) program. Understanding weed emergence patterns is critical for developing effective IWM strategies. The objective of this study was to evaluate effect of tillage timings and residual herbicides on cumulative emergence and emergence pattern of Palmer amaranth. Field experiments were conducted in 2015 and 2016 in a field naturally infested with photosystem (PS) II and 4- hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor-resistant Palmer amaranth near Shickley, Nebraska in a bare ground study, with no crop planted in the plots but residues from the preceding corn crop were present on the soil surface. Treatments consisted of shallow tillage timings (early, mid, and late), three premix corn or soybean residual herbicides, and a nontreated control. The Weibull function was fitted to cumulative Palmer amaranth emergence with day of year (DOY) and thermal time (TT) as independent variables. Year by treatment interaction was significant for time to 10%, 25%, 50%, 75%, and 90% Palmer amaranth emergence and cumulative emergence. Majority of Palmer amaranth seedlings emerged early, following early-tillage with 90% cumulative emergence occurring on DOY 172 compared with DOY 210 to 212 for mid- and late-tillage and DOY 194 in nontreated control in 2015. In 2016, 90% of cumulative emergence following early-, mid-, and late-tillage (DOY 201 to 211) were similar, and nontreated control (DOY 188) was similar to early-tillage. Nontreated control and PRE herbicide treatments had similar DOY values for 90% emergence in both years. Number of emerged Palmer amaranth seedlings over the season was higher with shallow tillage than no tillage or with PRE herbicides.