Eleven field experiments were conducted during 1994 and 1995 to compare rhizomatous johnsongrass control and soybean yield with single POST applications of quizalofop-P, fluazifop-P, clethodim, and sethoxydim at costs of $9.88, 19.76, 29.64, and 39.52/ha for each graminicide. Cost of the manufacturer's suggested use rate for these graminicides was approximately $29.64/ha, which corresponded to 0.09, 0.22, 0.14, and 0.27 kg ai/ha for these respective graminicides. When applied at a cost of $9.88/ha, quizalofop-P controlled rhizomatous johnsongrass more effectively than the other graminicides in five of 11 experiments. Quizalofop-P and fluazifop-P controlled johnsongrass similarly when applied at higher costs per hectare in 10 of 11 experiments. Sethoxydim was less effective than quizalofop-P or fluazifop-P in most instances, especially when graminicides were applied at costs of $9.88 or $19.76/ha. Clethodim was generally more effective than sethoxydim. Fluazifop-P and clethodim controlled rhizomatous johnsongrass similarly in six of 11 experiments regardless of cost. Differences in rhizomatous johnsongrass control among graminicides did not always translate into differences in soybean yield, although graminicides increased yield over the nontreated control in most experiments regardless of the graminicide cost. In several experiments, soybean treated with clethodim or sethoxydim applied at a cost of $9.88/ha yielded lower than when applied at higher costs.

Oxeye daisy has invaded seeded pastures, roadsides, and mountain rangelands in western Montana. In 1990, we began a study to: (1) determine use of oxeye daisy and introduced perennial grasses by cattle; (2) determine effects of intensive cattle grazing on the number of oxeye daisy seeds in the soil; and (3) assess effects of intensive grazing on year-to-year changes in oxeye daisy and associated perennial grasses. Cattle grazed oxeye daisy but much of their impact was from trampling or removing stems. The number of oxeye daisy seeds in the soil seedbank was lower in 1992 than in 1990 in grazed areas, whereas the number was higher in ungrazed areas. Two years of intensive grazing reduced densities of oxeye daisy seedlings and rosettes, but did not change densities of mature stems. Intensive grazing had minimal impact on the introduced grasses.

This research was designed to determine if sethoxydim-resistant corn hybrids exhibited levels of cross-resistance to other acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides. Three sethoxydim-resistant hybrids were tested in 1995 and four in 1996. The hybrids were treated with the 1 × (labeled use rate for annual grass control) and 4 × rate of clethodim, fenoxaprop-P plus fluazifop-P, fluazifop-P, quizalofop-P, and sethoxydim. At the 1 × rate, similar levels of corn safety were observed in both years with sethoxydim, quizalofop-P (except Asgrow RX620SR in 1995), and in 1996, fenoxaprop-P plus fluazifop-P. Corn treated with the 4 × rate of sethoxydim did not exhibit injury, while all other ACCase-inhibiting herbicides cause > 50% corn injury. Sethoxydim-resistant com hybrids used in this study did not consistently exhibit acceptable levels of cross-resistance to other ACCase-inhibiting herbicides. The use of clethodim will control volunteer sethoxydim-resistant corn in rotational crops.

Field experiments were conducted from 1993 to 1995 to evaluate the response of ALS-resistant and ALS-susceptible corn to imazethapyr, imazaquin, chlorimuron, and CGA-152005 at label and twice label rates applied preplant incorporated (PPI) and postemergence (POST). The susceptible hybrid (P3245) and the resistant hybrid (P3245IR) grain yield were not different where weeds were removed by hand-weeding alone. Alachlor plus atrazine alone plus hand-weeding reduced grain yield by 5% compared to hand-weeding only. Imazethapyr applied PPI and POST reduced height of the susceptible hybrid 11 and 6%, respectively, averaged across imazethapyr rates. Imazaquin reduced the final height of the susceptible hybrid by 30 to 75% and reduced corn density by 62 to 78%. Chlorimuron applied PPI reduced final corn height of the susceptible hybrid by 26 to 36% and density by 27%. Chlorimuron applied PPI and imazaquin applied PPI and POST reduced grain yield of the susceptible hybrid. Imazethapyr did not reduce grain yield of the susceptible hybrid, regardless of application timing or rate. Imazethapyr, imazaquin, and chlorimuron did not reduce height, density, or grain yield of the resistant hybrid, regardless of application timing or rate. CGA-152005 applied PPI reduced grain yield of the susceptible and resistant hybrid. CGA-152005 applied POST did not reduce grain yield, regardless of hybrid or rate.

An educational software program was developed to demonstrate the interactions among weed population demographic processes, plant community interactions, and grassland noxious weed management options. The software includes an example model parameterized to simulate yellow starthistle population dynamics and graphic output. The software allows students to change weed and competing grass population demographic parameters, herbicide, and biological control management options. The graphic output allows the user to observe the outcome of integration of weed biology and various weed management options.

Optimal application timing for dicamba–acetamide tank mixes was examined in field studies conducted in Michigan and Wisconsin from 1993 to 1995. Dicamba was tank mixed with alachlor, metolachlor, or SAN 582H and applied at planting, 7 d after planting, and 14 d after planting. Additional dicamba plus alachlor tank mixes applied at all three timings were followed by nicosulfuron postemergence to determine the effects of noncontrolled grass weeds on corn yield. Delaying application of dicamba–acetamide tank mixes until 14 d after planting often resulted in lower and less consistent giant foxtail control compared with applications at planting or 7 d after planting. Corn grain yield was reduced at one site where giant foxtail control was lower when application was delayed until 14 d after planting. Common lambsquarters control was excellent with 7 or 14 d after planting applications. At one site, common lambsquarters control and corn yield was reduced by application at planting. Dicamba–alachlor tank mixes applied 7 d after planting provided similar weed control or corn yield, while at planting and 14 d after planting applications provided less consistent weed control or corn yield than a sequential alachlor plus dicamba treatment or an atrazine-based program.

Agricultural production in China occurs via three distinct organizational units: the countryside farmer, state farms, and military farms. The countryside farmer in northeast China carries out most production operations with hand tools, some animal and tractor power, and little additional mechanization. Most weeds in row crops are controlled by hand, although a high percentage of the rice crop is treated with herbicides as is about 20% of the wheat. Countryside farmers independently manage small plots of land. State and military farms, the majority of which are located in China's northeastern-most province of Heilongjiang, are highly mechanized and accomplish most weed control with herbicides. Military farms range from ~500–2,500 ha, and state farms generally occupy 50,000–100,000 ha, with some much larger. Primary crops on the military farms are soybeans, oilseed rape, and wheat. State farms generally have more diversity in crops. The need for herbicide adjuvants to increase postemergence (POST) herbicide efficacy and for reduced tillage practices to combat soil erosion are recognized concerns, as is the threat of herbicide resistance.

Feral rye and jointed goatgrass are winter annual grasses that infest winter wheat in the western United States. Currently, no herbicides are available that selectively control these weeds in wheat. Because of this constraint, producers need cultural practices that reduce the seed densities of these two grasses in the soil seedbank. This research shows that applying nitrogen 5 mo before wheat planting and increasing the seeding rate with a tall wheat cultivar reduces seed production per plant of either species by > 40%. However, tall wheat cultivars usually yield less grain than semidwarf cultivars. Producers can avoid this yield loss by combining narrow rows with time of N application and increased seeding rate of semidwarf cultivars. This combination reduces weed seed production similarly to cultural systems with tall cultivars.

The lack of evolution of weed resistance to the herbicide glyphosate has been considered from several perspectives. Few plant species are inherently resistant to glyphosate. Furthermore, the long history of extensive use of the herbicide has resulted in no verified instances of weeds evolving resistance under field situations. Unique properties of glyphosate such as its mode of action, metabolism, chemical structure and lack of residual activity in soil may explain this observation. Selection for glyphosate resistance of crops using intense whole plant and cell/tissue culture techniques, including mutagenesis, has had only limited success and is unlikely to be duplicated under normal field conditions. Information obtained in the development of glyphosate-resistant crops suggests that target-site alterations that decrease the herbicidal activity of glyphosate also may lead to reduced survival of a weed. In addition, the complex manipulations that were required for the development of glyphosate-resistant crops are unlikely to be duplicated in nature to evolve glyphosate-resistant weeds.

A small -plot, pneumatic applicator was developed to apply either granular herbicide formulations or liquid herbicides impregnated on commercial dry fertilizer to field research plots. Pre-weighed herbicide samples poured into a stainless steel, motor-driven belt, cone seeder are automatically sput into four subsamples in a four-outlet rota seed distributor run by a 12-volt electric motor, and delivered to four plastic venturi chambers. A gasoline engine-powered leaf blower forces air through a 10-cm diam polyvinylchloride (PVC) pipe to the input sides of the venturi chambers. The forced air stream carries the herbicide samples through 2.5-cm diam flexible plastic tubing to four deflector shields mounted 61 cm apart on a fiberglass boom. The applicator uniformly delivers granules up to 400 kg/ha in a 2.5-m wide swath.

Oviposition site preferences for Galerucella calmariensis and G. pusilla, biological weed control agents against purple loosestrife, were examined in 1994 and 1995. The leaves, stems, axils, and flower buds (G. pusilla did not oviposit on flower buds) were found to be the preferred oviposition sites. Oviposited egg masses may be used as a parameter within a biological control monitoring plan, providing information on Galerucella establishment and/or presence, estimating future population size, and providing biological control agent dispersal information. Monitoring for egg masses should concentrate on host plant leaves, where over 56% of all egg masses were oviposited.

Redroot pigweed (Amaranthus retroflexus L.), one of the New World's major weeds, was described in 1753 by Carolus Linnaeus in Species Plantarum. Over three decades later (1789), the genu wa placed in Amaranthaceae by Antoine Laurent de Jussieu (1748–1836) (Britton and Brown 1898). Amaranthaceae belongs to Centrospermae, a group of familie that contain betalain pigments instead of the anthocyanins found in most other angiosperms; it is closely related to Chenopodiaceae (Heywood 1993).

Although economic thresholds are often used to make insect control decisions, the use of thresholds for weed management has been limited. Surveys of growers, agricultural chemical dealers, and farm managers/rural appraisers helped identify limitations to grower acceptance of economic thresholds for weed management. Most growers were concerned about harvest problems due to weeds, with 64% identifying this factor as a major limitation. Landlord perception and weed seed production were identified by 38% of the growers as major limitations, while 36% of the growers listed general appearance of the field as reasons. In contrast, 75% of the agricultural chemical dealers and 63% of the farm managers surveyed listed field appearance as a major reason limiting grower acceptance of economic thresholds for weed management. Since grower concerns involve risk management and future profitability, economic weed thresholds that address long-term costs and benefits of weed control decisions may be more fully accepted.

This paper describes the design, construction, and operation of tilted beds to investigate the effectiveness of vegetative filter strips (VFS) in removing agricultural chemicals from runoff water. The beds are designed to catch surface runoff, leachate, and subsurface lateral flow. Switchgrass was established on beds filled with Cullen clay loam or Emporia sandy loam. Switchgrass establi shed on Cullen clay loam beds reduced surface runoff by 60% and by 11% in sandy loam containing switchgrass compared to respective bare soils. Infiltration was 64, 26, 17, and 8% for clay loam with switchgrass, clay loam without switchgrass, sandy loam with switchgrass, and sandy loam without switchgrass, respectively.

Characterization of herbicide dissipation under field conditions is an important component in determining the environmental impact of herbicides, and much information is available on this subject. However, this research area could be improved by standardizing and implementing several quality control procedures. The purpose of this review is to evaluate the recent literature on herbicide dissipation published in journals of the Weed Science Society of America. This review is not comprehensive with respect to all experimental parameters associated with field dissipation studies, but it is aimed at addressing specific areas of concern in the experimental approach to this research.

SAN 582 at 1.1, 1.2, 1.3, 1.5, and 1.6 kg ai/ha; alachlor at 1.7, 2.2, and 2.8 kg/ha; and metolachlor at 1.7, 2.2, and 2.8 kg/ha were applied preemergence without and with atrazine at 1.7 kg/ha in no-till corn at two locations near Blacksburg, VA, in 1993 and 1994. SAN 582, alachlor, and metolachlor controlled TR-smooth pigweed when applied without or with atrazine, and with only a few exceptions, control was greater than 60%. The highest rate of individual herbicides was more effective than the lowest rate in most cases. Early control of TR-smooth pigweed was similar from all three herbicides, especially at higher rates, but control later in the season tended to be best with alachlor. As expected, atrazine applied alone did not control TR-smooth pigweed, and crop yields were increased with herbicide treatments compared to no treatment.