During field experiments the Russian knapweed nematode formed no galls on artichoke, one sterile gall on American basketflower, and few nematodes in numerous small galls on southwestern basket flower in comparison with much higher nematode production per gall on Russian knapweed.

One year after application under irrigated conditions, atrazine at 1.2 kg/ha injured oat but there was no effect after two years. On dryland, wheat and barley were injured for up to two years after atrazine was applied at 1.5 kg/ha. Atrazine concentrations in the soil were related to accumulated rainfall in an exponential equation. The equation predicted that, under the most severe drought conditions ever recorded for southern Alberta, injury to cereal crops could occur for at least three years after atrazine application at 1.2 to 1.5 kg/ha. Cyanazine did not injure subsequent crops under either irrigated or dryland conditions.

Field studies were conducted in 1991 and 1992 at the Faculty Farm of the U.A.E. Univ., Al-Ain, to evaluate the effectiveness of soil solarization for weed management in naturally infested plots of lettuce, and on subsequent planting of garlic. Solarization for 2 mo during the hottest summer period effectively suppressed weeds during the growing season of head lettuce. In subsequently-planted garlic, no significant effect was observed between solarized and nonsolarized treatments.

Weed control and cotton yield with a herbicide program of sethoxydim and DPX-PE350 applied postemergence over-the-top was compared with that of a standard herbicide program of trifluralin applied PPI plus fluometuron applied PRE plus methazole and MSMA applied postemergence-directed. Control of pitted and entireleaf morningglory, smooth pigweed, and prickly sida was similar with the postemergence over-the-top program and the standard herbicide program when DPX-PE350 was applied to cotton in the V2 or V4 growth stages. Less weed control and lower yield were observed when DPX-PE350 was applied to V6-stage cotton. Good control of annual grasses was obtained with all herbicide programs.

The response of potted ‘Cleopatra’ mandarin citrus seedlings to metalaxyl applied as a mixture with metolachlor, simazine, or bromacil, or as a sequential application after the herbicides was investigated under screen house conditions. The soils were drenched with herbicides at 2.5 ppmw (mg kg−1 soil dry wt basis) in tank-mixes with metalaxyl or metalaxyl was applied as a soil drench at 5, 50, and 250 ppmw 1, 2, 3, and 4 wk after herbicide application. Citrus seedling response to treatment was dependent on the presence or absence of herbicide, metalaxyl concentration, and the time following application. Fresh weights of citrus treated with 5 ppmw metalaxyl after herbicide application were no different from those treated with the mixture. Metalaxyl at 5 and 50 ppmw alone or with metolachlor did not affect citrus seedling fresh weight. However, delaying metalaxyl application at 50 ppmw by 3 or 4 wk after simazine and bromacil increased citrus seedling fresh weight as compared with the tank-mix. Separate applications of metalaxyl at 250 ppm reduced citrus seedling fresh weight less than the mixture for all the herbicides.

A survey determined the views of individuals in seven groups comprising the weed science community in the corn belt (primarily in Illinois) for importance of 8 environmental and 14 crop production issues and 16 weed species in setting weed science research priorities for the next 3 to 5 yr. The survey also considered if funding of research to solve these environmental and production issues should be from the private or public sector. Velvetleaf, foxtail species, and common lambsquarters were considered the top three weed species by all respondents, and each of these weeds was among the five most important weeds within each of the seven survey groups. Improving ground and surface water quality were the foremost environmental issues for all respondents, but soybean growers listed herbicide carryover as their top environmental concern. Reducing herbicide residues in food and developing sustainable practices were given low preference by all groups. Sustainable growers rated reducing herbicide carryover and minimizing applicator exposure as their lowest priorities. Among all respondents, the top three production issues were improved weed control in conservation tillage, more economical weed control, and improved integrated control strategies. Studying the biology/life cycles of weeds was the third highest production priority of University and U.S. Department of Agriculture (USDA) weed scientists, but was the last choice when averaged over the aggregate survey group. Developing strategies for resistant weeds and herbicide-resistant crops were chemical dealers top two priorities. Industry representatives gave the former subject their highest rating and the latter their lowest rating. Crop consultants seemed to want decision aids, as they chose assessing weed loss/thresholds and developing weed control/economic models among their top three production issues. Both corn and soybean growers desired more economical weed control as a first choice, while sustainable growers wanted improved cultural control strategies. Corn and soybean growers ranked developing new herbicides among their top three choices, but this issue was the lowest choice of the sustainable growers. University, USDA, and industrial weed scientists suggested that their own organizations conduct the research on their highest priorities issues.

Efficacy of herbicide programs containing clomazone PPI plus fluometuron PRE or clomazone plus pendimethalin PPI plus fluometuron PRE was compared with that of standard programs of pendimethalin PPI plus fluometuron PRE and norflurazon PPI plus norflurazon and fluometuron PRE. Cotton injury was less than 5% with all treatments when disulfoton or phorate was applied in the seed furrow. Control of fall panicum, goosegrass, large crabgrass, eclipta, entireleaf morningglory, ivyleaf morningglory, pitted morningglory, tall morningglory, prickly sida, redroot pigweed, smooth pigweed, hemp sesbania, spotted spurge, sicklepod, and velvetleaf and cotton yields with 0.8 kg ai ha−1 of clomazone plus fluometuron or 0.6 kg ha−1 of clomazone plus pendimethalin plus fluometuron equalled or exceeded that from the standard herbicide programs. POST-directed application of methazole at 0.8 kg ai ha−1 plus MSMA at 2.2 kg ae ha−1 increased sicklepod and morningglory control and cotton yield. Clomazone applied PRE at 0.6 kg ha−1 with fluometuron controlled broadleaf signalgrass, goosegrass, large crabgrass, prickly sida, and smooth pigweed equally with that of standard treatments of trifluralin or trifluralin plus norflurazon PPI and fluometuron PRE, whereas pitted morningglory control and cotton yield with clomazone plus fluometuron exceeded that with the standards.

The efficacy of reduced rates of POST herbicides for weed control in sweet corn was evaluated over a three-year period in field studies conducted at the Horticultural Experiment Station, Simcoe, Ontario. POST applications of metolachlor/cyanazine, cyanazine/atrazine and metolachlor/atrazine at 1/2X and 1/4X of labelled rates controlled broadleaf weeds comparable to that of standard labelled rates. Control exceeded 94% each year. Annual grass control was reduced with below-label rates, especially for cyanazine/atrazine and metolachlor/atrazine. A 1/2X application of nicosulfuron/rimsulfuron, following the 1/4X rate of cyanazine/atrazine, significantly improved grass control, compared to cyanazine/atrazine applied alone. Below-label rates did not result in decreased sweet corn yields.

Leafy spurge control with four herbicides was evaluated at nine sites in six Great Plains states. Sulfometuron alone did not control leafy spurge satisfactorily 12 mo after treatment (MAT). Sulfometuron plus dicamba at 105 plus 2240 g ai ha−1, when spring- or fall-applied, averaged 26 and 89% control and 31 and 86% grass injury, respectively, 12 MAT. Sulfometuron plus picloram at 105 plus 560 g ai ha−1, when spring- or fall-applied, averaged 63 and 92% control and 19 and 89% grass injury, respectively, 12 MAT.

A brief evolutionary description is given of the development of the discipline of weed science in the United States. Topics discussed include public recognition of weed science, losses from weeds, allocation of resources, herbicide usage, and future predictions of the development of the discipline. Weed scientists have had a major impact during the past four decades in increasing crop yields and reducing labor requirements for controlling weeds in crop production systems. Weed scientists have been so effective that recognition of their contributions and impact have often been overlooked in academic institutions but not in private industries that have staffed for herbicide development.

Little lovegrass, an annual species native to Europe, was not listed in the floras that describe the plants of Idaho and Washington. Twelve collections were made between 1984 and 1992 from four Idaho counties and six Washington counties. Those records extended the range of this species 450 to 1000 km northwest of populations reported in the literature. Approximately 600 km separated the furthest of the new collection sites, indicating widespread naturalization in those states. Eight of the collections were from roadsides, suggesting that human transport technology had a substantial influence on this plant's dispersal.

Combinations of rotary hoeing, cultivation, and band- or broadcast-applied herbicides were compared for weed management in corn at 64 locations in Iowa from 1987 to 1991. Cultivation alone resulted in denser weed populations than herbicide treatments at 41% of the locations; however, corn yields were reduced at only 22% of the locations when weeds were controlled mechanically rather than with herbicides. Compared with broadcast applications, herbicides applied in a band resulted in increased weed populations at 8% of the locations; however, corn yields were reduced at only 1% of the locations.

A method to rapidly identify acetolactate synthase/acetohydroxyacid synthase (ALS/AHAS)-resistant weeds is described based upon the differential accumulation of acetoin in the presence and absence of an ALS/AHAS inhibitor herbicide. Acetoin accumulation is induced by inhibition of ketol-acid reductoisomerase (KARI), the enzyme immediately following ALS/AHAS in the biosynthesis of branched-chain amino acids. Inhibition of ALS/AHAS prevents the build up of acetoin and forms the basis for distinguishing between sensitive and resistant biotypes. A new inhibitor of KARI, 1,1-cyclopropanedicarboxylic acid (CPCA), is described and was found to cause acetoin accumulation in velvetleaf leaf disks over the concentration range of 2 to 100 000 μM. In the presence of CPCA, a number of species important to monitor for ALS/AHAS resistance were found to accumulate acetoin at rates sufficient for resistance diagnosis in 2 to 8 h. In velvetleaf, the youngest apical leaf was found to be the most active in acetoin accumulation. The resistance diagnosis method was validated by clearly distinguishing between imazaquin-sensitive and imazaquin-resistant cocklebur biotypes.

Weeds reduce the livestock production from pastures and impose control costs on producers and governments. Economic assessments of pasture weed problems are required on and beyond the farm for planning private and public weed control. This requirement has several dimensions that can be used to demonstrate the economic effect of weeds and encourage weed control by the private and public sectors. This paper discusses the economic problems of pasture weeds and the procedures for multi-level economic assessments with a major pasture weed in Australia as an example, and demonstrates the important private and social economic benefits from controlling this weed.

Cogongrass [Imperata cylindrica (L.) Beauv. # IMPCY] is an aggressive, pernicious, rhizomatous perennial in the Poaceae (Graminae). It is native to tropical and subtropical areas of the eastern hemisphere. Introductions of cogongrass into the southeastern United States have been tracked to several separate sources, both accidental and intentional, in southern Alabama, southern Mississippi, and Florida. It was found to be unacceptable for use as a forage and in erosion control. Cogongrass is a highly variable species and has adapted to a variety of environmental conditions in its native and introduced range. Today cogongrass infests 200 million ha in Asia, several thousand ha in the Southeastern United States, and over 500 million ha worldwide. It has been reported to be a weed problem in many annual and perennial crops. In addition to competing for light, water and nutrients, cogongrass interference is caused by alleopathy and physical injury when rhizome apices penetrate crop roots, bulbs, and tubers. Holm et al. designated cogongrass as the world's seventh worst weed.

Broadleaf weed control with DPX-PE350 at 56, 84, 110, 140, and 170 g ae ha−1 applied postemergence was evaluated. DPX-PE350 was less effective and higher rates were required when applied to three- to six-leaf weeds compared to one- to two-leaf weeds. Listed in order of increasing susceptibility are sicklepod, tall morningglory, pitted morningglory = palmleaf morningglory, and entireleaf morningglory = hemp sesbania = velvetleaf.

A 2-yr field experiment was conducted at Fayetteville and Stuttgart, AR, to predict soybean yield loss as a function of barnyardgrass density and total dry weight. Predicted soybean yield reductions were 0 to 78% for original densities of 1 to 500 barnyardgrass plants per m of row. Soybean yield reductions were linear from 0 to 150 barnyardgrass plants per m of row with an average yield reduction of 0.25% for each plant per m of row. Soybean yield was reduced 10, 25, and 50% from original barnyardgrass densities of 42, 110, and 250 plants m of row. Predictions of soybean yield reduction from barnyardgrass dry weight and original density were similar. traspecific interference of barnyardgrass occurred for all variables tested, with individual barnyardgrass plants becoming less competitive as density increased.

Serrated tussock [(Nassella trichotoma (Nees) Hack. # STDTR] is a clump-forming, perennial, cool season grass. It is native to South America, where it occurs in Argentina, Brazil, Chile, Peru, and Uruguay. In the past century, it has been introduced to New Zealand, Australia and South Africa, and also occurs in small acreages in France, Italy, and the United Kingdom. Serrated tussock occurs in fields, wastelands, and pastures, but rarely in wet or shaded areas.

In 1990, a broadleaf weed growing on a cattle ranch in Hendry County in southwest Florida was identified as tropical soda apple (Solanum viarum Dunal), a species native to Argentina and Brazil (5) (Figure 1). Tropical soda apple (TSA) was apparently collected in Florida from Glades County in 1988 (University of Florida Herbarium) but was observed on the Hendry County ranch as early as 1987. Having foliage unpalatable to livestock, this noxious weed can infest a pasture or rangeland within one to two years resulting in lower stocking rates (animals per hectare). However, livestock and wildlife (feral hogs, deer, raccoons) will eat the fruit and disseminate the seed via feces. Fruit production occurs throughout the year (primarily September through May) thus providing high numbers (40000 to 50 000 per plant) of viable seed (75% germination) for seed dispersal. Our objectives are to alert those concerned with weed control of the presence of TSA in subtropical regions of the U.S., to discuss the ecology and taxonomy of this weed, and to indicate areas for future research.