Weed management during alfalfa (Medicago sativa L.) establishment is a major concern for producers in the northeast USA. The objectives of this research were to determine the yield, quality, and economic consequences of controlling weeds during the establishment of spring‐ and summer‐seeded alfalfa. Alfalfa was band‐seeded during spring (April and May) and late summer (August and September) into a conventionally tilled seedbed of Hagerstown silt loam (fine‐loamy, mixed, mesic Typic Hapludalfs) at Landisville, PA, in 1991 and Murrill silt loam (fine‐loamy, mixed, mesic Typic Hapludult) at Rock Springs, PA, in 1991 and 1992. Weed control treatments for the spring seedings included: (i) no herbicide or nurse crop (no weed control); (ii) oat (Avena sativa L.) nurse crop; (iii) benefin preplant incorporated; and (iv) sethoxydim and 2,4‐DB postemergence. Weed control treatments for late‐summer seedings were the same as those in the spring except that the nurse crop was replaced with a paraquat application to dormant alfalfa. Seeding alfalfa later, compared with earlier, in the spring tended to increase weed and decrease alfalfa dry matter (DM) yield but did not affect total DM yield or forage quality during the seeding year. For spring‐seeded alfalfa, weed control treatment effects on alfalfa and weed DM yield during the seeding‐year were sporadic, however, net economic return per acre was generally greatest when no weed control was used. Neither time of spring seeding nor weed control treatments produced consistent differences in yield, quality, or net economic return per acre after the seeding year. Delaying alfalfa seeding in the summer reduced first harvest alfalfa yield (704 lb/acre less) and season total alfalfa yield (1121 lb/acre less) compared with early seedings. Generally, weed control treatments in summer‐seeded alfalfa did not improve alfalfa or total DM yield, forage quality, or net economic return per acre compared with no weed control. We conclude that when alfalfa is either spring or summer seeded, the weed control practices used in this study were not economically beneficial and may actually reduce net return per acre because of associated additional costs compared with seeding alfalfa with no companion crop or herbicide. Research Question Concerns over the perceived deleterious effects of weeds on alfalfa survival and forage quality cause many producers to employ a prophylactic weed control practice during alfalfa establishment. These practices not only add to the cost of forage production, but also can involve the use of chemicals, which are increasingly under environmental scrutiny. This study examines the effect of different weed control practices during alfalfa establishment on forage yield and quality and net economic return per acre. Literature Summary Weed management during alfalfa establishment is important for improving forage yield and quality on the approximately 250 000 acres planted to alfalfa each year in the northeast USA. Numerous practices, including nurse crops, herbicides, and time...

Influences of a hairy vetch cover crop and residual herbicides were examined in field corn in 1991 and 1992. Hairy vetch was seeded in mid-August and killed the following May with tillage, mowing, or glyphosate plus 2,4-D (no-till). These cover crop management systems were compared with a no-cover treatment. Residual herbicides including atrazine plus metolachlor applied PRE at three rates and nicosulfuron plus thifensulfuron applied POST at a single rate were compared within cover crop management systems. All cover crop management systems effectively controlled hairy vetch except mowing in 1992. The corn population was reduced in mow treatments containing uncontrolled vetch. Hairy vetch mulch suppressed some weeds in the no-till treatments in 1991, but more annual grass was noted late in the season with no-till into hairy vetch than with the no-cover treatments in 1992. Residual herbicide performance was similar across cover crop management systems, except for fall panicum control which decreased in some no-till systems. Unlike soil-applied herbicides, performance of POST herbicides was unaffected by cover crop management systems.

Postemergence applications of nicosulfuron and primisulfuron were compared to preplant glyphosate and atrazine plus simazine for quackgrass control in reduced tillage and no-till corn. The level of quackgrass control was reduced by no-till practices. At 6 wk after planting, glyphosate and atrazine plus simazine were most effective in controlling quackgrass. Quackgrass biomass 12 wk after planting indicated that the performance of the herbicides were generally similar, although primisulfuron was less effective in no-till. One year after corn planting, levels of quackgrass control in the tilled plots were the same as or better than in the no-till treatments. Atrazine plus simazine was the most effective herbicide treatment over tillage systems, while primisulfuron was the least effective.

Studies were conducted during a 2-yr period measuring corn silage and grain yield and velvetleaf seed production in response to velvetleaf density. Velvetleaf densities of 0, 2, 5, 10, and 21 plants/m2were established in conventionally tilled corn. The percent corn yield reduction in response to velvetleaf density was similar for both years despite differences in total corn yield. Corn grain and silage yield responded differently to velvetleaf interference. Although both were adversely affected, silage yield reductions were twice that of grain at the low velvetleaf densities. A hyperbolic yield model predicted a maximum yield loss for corn silage and grain of 36 and 37% with incremental losses of 7 and 3%, respectively, as velvetleaf density increased. Velvetleaf seed production ranged from 2,256 to 4,844 seed/m2from the lowest to the highest density. This study demonstrates that corn silage yield is more sensitive than corn grain yield to velvetleaf interference, as well as how crop value plays an important role in determining economic thresholds. Finally, this research confirms the prolific nature of velvetleaf and shows that even at low densities, velvetleaf seed production could affect weed control decisions for many seasons to come.

Imazethapyr is registered for weed control in pure alfalfa and in established alfalfa‐grass mixtures. Orchardgrass (Dactylis glomerata L.) and timothy (Phleum pratense L.) tolerance to imazethapyr during establishment was examined in the greenhouse and in mixtures with alfalfa (Medicago sativa L.) in the field. Imazethapyr was applied following grass emergence at rates ranging from 0.5 to 1.5 oz ai/acre at three different stages of forage grass growth. In the greenhouse, application of imazethapyr to seedling timothy was more injurious than to seedling orchardgrass. Imazethapyr application to timothy reduced grass growth 19 to 48% in the greenhouse, while orchardgrass growth was reduced no more than 26%. Imazethapyr reduced 2‐leaf timothy yield more than 4‐ or 7‐leaf grass in the greenhouse study, while both 2‐ and 4‐leaf orchardgrass yield was less than 7‐leaf grass. In the field, injury from imazethapyr to timothy was greater than to orchardgrass when the herbicide was applied following the first harvest, especially during a drought year. Imazethapyr reduced both orchardgrass and timothy growth in the field by as much as 34% on average regardless of application rate. Weed control was best at the early postemergence application timing and less effective at the mid‐post timing due to excessive weed size at application. Weed control after first harvest was not needed. Application of imazethapyr to mixed forages the year of establishment can reduce the grass component of the forage and could reduce total forage yield. Research Question Much of the hay and pasture in the northern USA is planted to legume‐grass mixtures. However, in the northeastern USA, no herbicides are labeled for alfalfa‐grass mixtures in the establishment year. Imazethapyr (Pursuit®), an imida‐zolinone herbicide, is labeled for control of broadleaf weeds and grasses in pure alfalfa seedings, established alfalfa, and established alfalfa‐grass mixtures. If imazethapyr could be safely used to control weeds in mixed seedings during the seedling year, it would greatly improve weed management options. The objective of this research was to evaluate the effect of imazethapyr rate and application timing on orchardgrass and timothy tolerance in the greenhouse and on spring‐seeded alfalfa‐orchardgrass and alfalfa‐timothy mixtures in the field. Study Description In the greenhouse, imazethapyr was applied at 0.5, 0.75, and 1 oz/acre to 2, 4, and 7‐leaf orchardgrass and timothy. In the field, imazethapyr was applied at 0.75, 1, and 1.5 oz/acre to alfalfa‐orchardgrass and alfalfa‐timothy mixtures when the grass component had 2 or 4 leaves and after the first forage cutting. No‐herbicide (control) treatments were included in both experiments. In the greenhouse study, forage grass dry weight was determined, while in the field, forage and weed component dry weights were measured independently up to two times during the establishment year and three to four times the year following establishment. In the greenhouse and field, data were subjected to analysis of varia...