Published online by Cambridge University Press: 12 June 2017
Field studies were conducted to document the response of itchgrass [Rottboellia exaltata (L.) L.f. ♯3 ROOEX] in soybean [Glycine max (L.) Merr. ‘Forrest’] to selected herbicides and postplanting cultivation. Early cultivation stimulated emergence of itchgrass seedlings; however, when plots were cultivated two or three times, itchgrass was effectively removed from the tilled area. Cultivation had no effect on the density, height, standing biomass, or seed production of itchgrass plants in the soybean row but did increase soybean yield. In response to a density reduction of 90%, the average weight, number of tillers and branches, and seed production of single itchgrass plants increased by a factor of 2.9, 3.1, 2.3 and 2.6, respectively, in trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine)-treated plots. Individual plants did not increase growth following density reduction by a postemergence application of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Itchgrass plants competing for the entire season in plots treated with trifluralin reduced soybean yield approximately 21 g per weed, while itchgrass recovering from diclofop treatment and competing the remainder of the season reduced yield approximately 5 g per weed.