The recent introduction of glufosinate-resistant and glyphosate-resistant crops provides growers with new options for weed management. Information is needed to compare the effectiveness of glufosinate and glyphosate on annual weeds. Greenhouse trials were conducted to determine the response of barnyardgrass (Echinochloa crus-galli), common lambsquarters (Chenopodium album), common ragweed (Ambrosia artemisiifolia), fall panicum (Panicum dichotomiflorum), giant foxtail (Setaria faberi), large crabgrass (Digitaria sanguinalis), and velvetleaf (Abutilon theophrasti) to glufosinate and glyphosate. The response of velvetleaf and common lambsquarters was investigated at multiple stages of growth. Glufosinate and glyphosate were applied to each weed species at logarithmically incremented rates. The glufosinate and glyphosate rates that provided a 50% reduction in aboveground weed biomass, commonly referred to as GR50 values, were compared using nonlinear regression techniques. Barnyardgrass, common ragweed, fall panicum, giant foxtail, and large crabgrass responded similarly to glufosinate and glyphosate. Common lambsquarters 4 to 8 cm in height was more sensitive to glufosinate than glyphosate. In contrast, 15- to 20-cm tall-velvetleaf was more sensitive to glyphosate than glufosinate.

Greenhouse studies were conducted to determine the response of velvetleaf, common cocklebur, and ivyleaf morningglory to mesotrione and atrazine applied PRE, and to characterize the nature of any interaction between mesotrione and atrazine. Sensitivity to mesotrione was as follows: velvetleaf > common cocklebur > ivyleaf morningglory. Sensitivity to atrazine was as follows: ivyleaf morningglory > common cocklebur > velvetleaf. Combinations of mesotrione and atrazine resulted in at least an additive interaction. The activity of mesotrione and atrazine applied in combination was generally additive for control of velvetleaf and ivyleaf morningglory but was synergistic for several rate combinations.

Greenhouse and field research was conducted to determine the effect of glufosinate, glyphosate, and glyphosate plus additional adjuvant on yellow nutsedge control and tuber production. Glyphosate at 0.84 kg/ha reduced yellow nutsedge dry weight 64%, whereas glufosinate at 0.4 kg/ha reduced dry weight only 22% when averaged over diammonium sulfate (DAS) and spray volume. Furthermore, yellow nutsedge dry weight was reduced 53% in the presence and 34% in the absence of DAS; however, dry weights were similar when spray volumes of glufosinate or glyphosate ranged from 140 to 1038 L/ha. Yellow nutsedge control with glyphosate and glufosinate increased to 88 and 68%, respectively, when the herbicides were injected into the plant. In the field, glufosinate at 0.4 kg/ha and glyphosate at 0.84 kg/ha controlled yellow nutsedge 19 and 53%, respectively. Glyphosate reduced yellow nutsedge tuber density 51%, tuber fresh weight 59%, and tuber sprouting 17% 42 wk after treatment in the field. The addition of nonionic surfactant, methylated seed oil, or crop oil concentrate to glyphosate plus DAS did not increase yellow nutsedge control with glyphosate in the greenhouse or field.