Field studies were conducted to determine the effect of soybean cultivar, tillage, and rye mulch on sicklepod growth. Early-season sicklepod height was not affected by tillage or mulch. Sicklepod was tallest when grown with ‘Centennial’ or ‘Biloxi,’ the tallest cultivars, and shortest when grown with a dwarf isoline of ‘Tracy M,’ the shortest cultivar. Soybean competition reduced early-season weed density by 30 to 50%, depending on the cultivar. Centennial and dwarf Tracy M caused a 30% reduction in early-season sicklepod biomass while ‘Sharkey’ and Biloxi reduced sicklepod growth by 40%. By late-season, sicklepod biomass reduction ranged from 18% (Tracy M) to 55% (Biloxi) and was directly related to soybean cultivar height. Mulch or no-tillage independently reduced sicklepod biomass.

Laboratory and greenhouse studies examined effects of atrazine, alachlor, and metolachlor on growth and colonization of grain sorghum roots by Macrophomina phaseolina, causal fungus for charcoal rot disease. In laboratory studies, all three herbicides reduced fungal colony diameter and increased production of microsclerotia. Alachlor and metolachlor reduced germination of fungal microsclerotia. Atrazine did not affect microsclerotia germination, but lessened the effects of alachlor and metolachlor on germination when applied in combination. In greenhouse studies, atrazine reduced numbers of M. phaseolina microsclerotia recovered from soil after 8 wk, and this resulted in reduced colonization of roots by this fungus at harvest. Colonization of grain sorghum roots by M. phaseolina was not affected by alachlor or metolachlor. Grain sorghum growth was reduced by atrazine at all intervals and by alachlor and metolachlor at harvest, despite use of seed safened with cyometrinil.

Trifluralin is used for weed control in wheat but may reduce vegetative growth and yield. Postemergence (POST) herbicides may cause additional plant stress to trifluralin-stressed wheat. Field studies at Groton, SD in 1991 and 1992 and at Highmore, SD in 1992 evaluated the effects of 2,4-D-amine, difenzoquat, metsulfuron, and a combination of fenoxaprop-ethyl + 2,4-D-ester + MCPA-ester on hard red spring wheat cultivars ‘2375,’ ‘Prospect,’ and ‘Butte 86’ seeded in areas treated with preplant incorporated trifluralin either in the spring before seeding (0.56 kg ai/ha) or the previous year (1.12 or 2.24 kg ai/ha). Trifluralin applied alone in the spring, and followed by some POST herbicides, reduced shoot dry weight and grain yield. Trifluralin reduced the yield of Prospect the most and the yield of 2375 the least. Yields of trifluralin-treated wheat were reduced 23% by metsulfuron and 14% by fenoxaprop-ethyl + 2,4-D + MCPA compared to yields of wheat treated with only the respective POST herbicide. Yields were not reduced with any trifluralin-POST herbicide combination when trifluralin was applied a year prior to seeding wheat.

Grass and broadleaf herbicides are available for effective, single-application total postemergence weed control in corn. Field experiments were conducted in 1992 and 1993 on sites with dense natural weed infestations to determine the effects of weed interference prior to herbicide application on corn yield. Nicosulfuron plus bromoxynil was applied at 5-, 10-, 15-, or 20-cm weed canopy heights in plots with or without weed interference. Crop injury was more severe when herbicides were applied to smaller corn. Herbicide applications made to 5-, 10-, or 15-cm tall weeds provided nearly complete weed control. Weed interference did not reduce corn height or grain yield when postemergence applications were made to weeds 10 cm or less in height. Weed interference reduced corn height and grain yield in 1992 when applications were made to 15-cm tall weeds even though weed control was nearly complete. Weed control was incomplete and corn height and grain yield were reduced when applications were delayed until weeds were 20 cm tall.

The effects of five soil fungi, endemic to the western United States, were evaluated for disease reaction, root dry weights and shoot dry weights on five grass species. The undesired grass, downy brome or medusahead, the perennial forage species, squirreltail or western wheatgrass, and winter wheat were susceptible to take-all. Downy brome, medusahead, squirreltail, and winter wheat were susceptible to crown rot. The desired grasses, squirreltail, western wheatgrass, and winter wheat, were susceptible to barepatch. Crown rot is adapted to dry soils and may be a potential biological control on downy brome and medusahead in the arid environment of the western U.S.

Propanil-resistant barnyardgrass was reported in Poinsett County, AR, in 1990. Greenhouse studies were initiated to determine the distribution of propanil-resistant barnyardgrass in the state and to characterize the resistance. Barnyardgrass seeds were obtained in 1991 and 1992 from fields in 19 of the 38 rice producing counties in Arkansas where propanil treatment at recommended rates gave unsatisfactory barnyardgrass control. Barnyardgrass seedlings from the various sources were treated with propanil at 4.5 kg ai/ha and seedling injury response was compared to the response of seedlings collected from known resistant and susceptible barnyardgrass populations. Propanil-resistance of varying levels was confirmed in 115 (16 counties) out of the 138 Arkansas barnyardgrass seed sources. Propanil I50 values (rate of herbicide required to provide 50% injury/control) were determined to be 14, 20, and 39 kg/ha for slightly, moderately, and highly resistant barnyardgrass, respectively. A resistance factor of 20® was found in the highly resistant barnyardgrass category. Development of resistance was highly correlated with crop rotations where rice was grown one out of two, or two out of three years.

Five sulfonylurea herbicides were applied to Typic Boroll soil with pH 8.0 and 2% organic matter in the field and growth chamber to assess their residual effects on following crops. Under irrigated conditions, triasulfuron at 22 g/ha reduced the growth of alfalfa, canola, corn, lentil, pea, potato, and sugarbeet the year after application but caused no injury after two years. Alfalfa GR50 (rate required to reduce growth by 50%) values immediately after application of chlorsulfuron, triasulfuron, and metsulfuron were < 2.2 g/ha and similar in the growth chamber and field. Alfalfa and canola GR50 values immediately after thifensulfuron application in the growth chamber were ≥ 90 g/ha. Alfalfa, canola, flax, and sugarbeet GR50 for tribenuron in the growth chamber were < 4 g/ha. Crop response curves developed by growth chamber experiments could replace many of the multiple site and crop field experiments now required to develop recropping guidelines for residual herbicides.

Adjuvants were evaluated to determine the effect on increasing spray droplet size and reducing the amount of spray dispensed in small driftable size particles when applying water and paraffinic oil at ultralow volume. Spray solutions were applied with an air-assist system at liquid flow rates of 28 and 56 ml/min and atomized with 14, 28, 42, 56, and 84 kPa of air pressure. Water and paraffinic oil were applied alone and with two drift retardant adjuvants mixed individually in each. The two water soluble adjuvants were mixed at concentrations of 0.25, 0.50, 0.75, 1.0, and 2.0%; oil soluble adjuvants were applied at 0.125, 0.25, and 0.50%. Adjuvants used in water and oil were effective at increasing droplet size and reducing the amount of liquid dispensed in small driftable size particles. Effectiveness of the adjuvants decreased as air pressures increased, with water soluble adjuvants being more susceptible to air pressure. Volume median diameters > 200 μm with water could be achieved without adjuvants; whereas with oil, an adjuvant was required.

Broccoli cultivars were evaluated for differential response to oxyfluorfen applied postemergence (0.1 to 1.6 kg ai/ha) in the greenhouse and post-transplant (0.125 to 1.0 kg/ha) in a spring and a fall field study. One cultivar, ‘Green Goliath,’ was injured more by oxyfluorfen than other cultivars in all environments. ‘Pinnacle,’ was consistently less injured than others. ‘Early Dawn’ and ‘Emerald City’ were intermediate in response to oxyfluorfen. At application rates of 0.25 kg/ha or less, all cultivars recovered sufficiently from injury to produce broccoli heads of equal weight and quality as controls. Cultivars differed in their tolerance of oxyfluorfen at rates above 0.25 kg/ha. Late-maturing cultivars (i.e., Pinnacle) usually recovered from injury to yield similarly to hand-weeded plots while early-maturing cultivars were more likely to show yield losses. Broccoli cultivars possess sufficient tolerance to oxyfluorfen applied post-transplant for weed control. Appropriate choice of cultivar will enhance its utility.

A carpeted roller applicator and broadcast sprayer were compared for application of glyphosate, metsulfuron, and picloram to control duncecap and tall larkspur on mountain range sites in southern Idaho and central Utah, respectively. Glyphosate was the most effective herbicide, controlling 96% of both larkspur species when applied by the sprayer and 78% when applied by the roller. There was no difference in larkspur control between application methods using metsulfuron or picloram. Application of herbicides by the carpeted roller was less detrimental to forbs compared to the sprayer, and the roller application of glyphosate did not reduce grass cover. Grass cover doubled following treatments with picloram and metsulfuron.

Standard operating procedures (SOPs) were developed for repetitive field research tasks to help ensure that instructions were complete and to provide consistency and continuity in the senior author's field research program. SOPs are explicit step-by-step instructions for carrying out experimental tasks that are components of experimental plans. SOPs are not the same as protocols for unique, new experimental plans. However, protocols may incorporate sequences of SOPs, if desired. SOPs are most useful for new workers and when research tasks need to be repeated infrequently in time (e.g., once every 6 mo or less per year). SOPs may help researchers enhance data accuracy, precision, and reproducibility as part of their own statistical quality control procedures. The authors' field-tested SOPs are available on diskette for critical review, modification, and use by interested weed scientists.

In 1753, Carolus Linnaeus described tansy ragwort, Senecio jacobaea, in Species Plantarum. This species is a member of the largest genus of the sunflower family (Asteraceae), which encompasses 1300 genera and 21 000 species worldwide. Taxa in the genus Senecio L. range from herbs to shrubs and occur globally. Comparatively few senecios are of economic importance and many of them are weeds, among them tansy ragwort, which can infest pastures, crowding out more desirable forage and poisoning grazing livestock.

The Weed Society of America (WSA) was organized in 1954. At that time, 114 scientists were identified as conducting research on weeds and their control, although only part of these scientists' time was devoted to weeds. Although “selective” herbicides were used in the late 1800s and the “sinox” or “dinitro” herbicides were fairly important from the 1930s, the discovery of the broadleaf selective phenoxy herbicides in the 1940s gave scientists and farmers an exciting new way to manage weeds and played a major role in advancing the notion that there was a need for a separate discipline of weed science. It was noted by C. J. Willard in 1954 at an address to the American Society of Agronomy (ASA) that there was an urgent need for research on weed biology and ecology and on the behavior of herbicides in plants and soils. WSA held its first meeting in January, 1956. There were 621 charter members of WSA.