Palmer amaranth (Amaranthus palmeri) is a major weed in corn (Zea mays) fields in the southern Great Plains of the United States. Field studies were conducted in 1996, 1997, and 1998 near Garden City, KS, to evaluate the effects of Palmer amaranth density and time of emergence on grain yield of irrigated corn and on seed production of Palmer amaranth. Palmer amaranth was established at densities of 0.5, 1, 2, 4, and 8 plants m−1 of corn row both concurrently at corn planting and when corn was at the three- to six-leaf stage. The control plots were weed free. The Palmer amaranth planted with corn emerged with corn, whereas that planted later emerged at the four-, six-, and seven-leaf stages of corn. The Palmer amaranth emerging with corn reduced yield from 11 to 91% as density increased from 0.5 to 8 plants m−1 of row. In contrast, yield loss from Palmer amaranth emerging later than corn was observed only when the emergence occurred at the four- and six-leaf stages. The corn leaf area index (LAI) decreased as Palmer amaranth density increased. Reduction in corn LAI from Palmer amaranth interference was smaller for the second emergence date than for the first emergence date. Seed production per Palmer amaranth plant decreased with greater density, but seed per unit area increased from 140,000 to 514,000 seeds m−2 at densities of 0.5 and 8 plants m−1 of row, respectively, when Palmer amaranth emerged with corn and from 1,800 to 91,000 seeds m−2 at the same densities for later emergence dates. Although Palmer amaranth is highly competitive in corn, this study shows that yield loss is affected more by time of emergence than by density.

Eight bull calves (four Holsteins and four Ayrshire calves with mean birth weight of 38.8 kg) were ruminally cannulated at 3 d of age and allocated to one of two weaning programs. All calves were fed colostrum for 3 d after birth and milk until weaning. Calves in the conventional-weaning program were fed a starter diet from 3 d of age and weaned at 6 wk of age. In the early-weaning program, calves were fed a highly palatable pre-starter diet from 3 d of age until they consumed 227 g/d, and then fed a mixture of pre-starter (227 g) and starter diet ad libitum. Calves in this group were weaned at 4 wk of age. Ruminal samples were collected at 3 and 7 d, then weekly thereafter through 8 wk and at 10 and 12 wk of age to assess microbial activity. Calves in the early-weaned group had a higher concentration of total ruminal volatile fatty acids at an earlier age than the calves in the conventional-weaning program. This was accompanied by a trend toward higher lactate concentrations and lower ruminal pH in the early-weaned group during their first 4 wk of age. Lactate and ammonia concentrations decreased with calf age. The total anaerobic bacterial counts increased slightly with calf age, whereas Streptococcus bovis and facultative bacterial populations decreased with calf age. Amylolytic, proteolytic, lactobacilli, lactate-utilizers, cellulolytic and methanogenic bacterial populations increased progressively in both groups. Cellulolytic and methanogenic bacteria were present in both groups at 3 d of age. No protozoa were detected in calves of either group. In general, the most significant changes in bacterial populations and metabolic activity in both groups occurred between 4 and 6 wk of age. Although calves in both groups had similar patterns of bacterial development, calves in the early-weaning program tended to have high ruminal microbial activity at an earlier age than the conventionally weaned calves.

Field and greenhouse studies were conducted in 1995 and 1996 in Kansas to determine the efficacy of 21 herbicide treatments for control of tumble pigweed, Palmer amaranth, redroot pigweed, and two biotypes of common waterhemp in soybean. In field studies, nine of eleven preemergence treatments controlled all four species 90% or more. However, pendimethalin and trifluralin controlled Palmer amaranth, redroot pigweed, and tumble pigweed less than the other preplant incorporated and preemergence treatments. With the exception of flumiclorac and NAF-75, postemergence treatments controlled 75 to 90% of all four species. A biotype of common waterhemp collected in Iowa was not controlled by acetolactate synthase-inhibiting herbicides. Greenhouse results were similar to field experiments. Results suggest at least 90% control of theseAmaranthusspecies is possible with proper herbicide selection.

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Acifluorfen, lactofen, chlorimuron, thifensulfuron, imazethapyr, and imazaquin were evaluated for control of Palmer amaranth, common waterhemp, redroot pigweed, and tumble pigweed at three application timings in field and greenhouse experiments. Results from field studies indicated that most herbicides provided greater than 90% control of common waterhemp, redroot pigweed, and tumble pigweed regardless of time of application. Palmer amaranth was the most difficult species to control, and only thifensulfuron and imazethapyr provided greater than 80% control at all application timings. In the greenhouse experiment, herbicides were applied when pigweeds averaged 10 cm, 20 cm, and 30 cm in height. Results were similar to the field experiment, except that common waterhemp was more difficult to control.