Imazamox-resistant hybrids resulted from a cross between jointed goatgrass and an imazamox-resistant wheat (cv. FS-4 IR wheat). Two imazamox-resistant hybrids were discovered in a research plot where FS-4 IR wheat seed had been replanted from the harvest of an imazamox efficacy study conducted the year before at a different location. These hybrid plants survived imazamox applied at 0.053 and 0.069 kg ai ha−1 in the field and produced seven viable seeds (BC1). This seed germinated, and chromosomes were counted from the roots (2N number ranged from 39 to 54). In the greenhouse, six of the seven plants survived an application of 0.072 kg ai ha−1imazamox, which confirmed that the resistance trait had been passed to these progeny. A large amount of phenotypic variation was observed in the mature BC1 plants. A genetic description of the movement of the resistant gene is proposed based on the case of the gene being located on the D and the A or B genomes. Management strategies to reduce the occurrence of herbicide-resistant hybrids are presented.

This symposium is a first in the history of our society. We have never before devoted a portion of the annual meeting to formal consideration of the ethical aspects of our work. It is significant to me that after 38 annual meetings, 42 years of existence, and 45 volumes of our journal, we have begun to discuss the ethics of weed science. I applaud the vision of the Board of Directors that provided funding to bring two of our speakers to the meeting. The Board has always provided capable management of the society's affairs. By management, I mean that we have been well organized to proceed in the direction we are headed. Voting to hold this symposium and providing funding is, in my view, an act of leadership, by which I mean, thinking about moving in a new direction, in a direction not dictated by the past. When disciplines proactively begin to examine the ethical dimensions of their science and technology, society may begin to believe that scientists recognize and act upon their social responsibilities. This would be a welcome and refreshing development in these days when public distrust and disillusionment with science may be as high as they have ever been (Lockwood 1997).

Weed science, like most sciences, has distanced itself from social and ethical discourse in theory and practice. This symposium illustrates my point. The 38th meeting of our society is the first time there has been a formal discussion of the ethical aspects of our work. Weed science, we often believe, is value free, as science ought to be. But neither basic nor applied weed science is value free; they are value laden. Operative values include meeting basic human needs through improved food production, promoting the common good through abundant food, improving people's lives through efficient production of safe food, achieving agricultural sustainability, and increasing efficient food and fiber production and farmer profit. Truth pursued via the scientific method is valued and respected, as is belief in the goodness of scientific and technological progress. Most of these values rest on an ethical foundation known as utilitarianism. Most weed scientists and their colleagues in agricultural sciences are utilitarian in that they believe their work should be useful to humans and should promote the greatest good for the greatest number of people. What weed scientists believe and stand for and the validity of the ethical foundation of their utilitarian convictions ought to be central subjects of the weed scientist's research and teaching. Ethical reflection does not necessarily imply criticism or a need for reform, but it does demand intellectual clarity and an ability to affirm who we are, what we do, and what we value. Weed scientists should engage in an exchange about the ideas that are the end result of their experiences and discuss the experiences that give shape, substance, and depth to those ideas. In the absence of internal ethical reflection and value clarification, external distortions—including public criticism—will define the moral universe weed scientists must work in. Without embarrassment, weed scientists have to learn to ask about the ethical foundation of their science.

Five goals for agriculture are proposed: profitable production, sustainable production, environmentally safe production, satisfaction of human needs, and compatibility with a just social order. Four ways to view the origin of potentially conflicting values expressed in the five goals follow. In view of the five goals and differing value positions, the most pressing question for weed science is to what extent current methods of weed control are compatible with a more sustainable and environmentally sensitive agriculture.

Weed Scientists, like many other agricultural scientists and natural resource land managers, often engage in debate with other members of society about values and perceptions of food and fiber production. The focus of the debate is usually on the tools and tactics to grow crops, produce wood, or manage grazing land. Environmental ethical issues have dominated discussions among the membership of WSSA for decades. Examples include the decade-long debate over 2,4,5-T use in forestry and now water quality and human health concerns about atrazine use in agriculture. Ecology is a scientific discipline that seeks knowledge about the interactions of organism, their environments, and, more broadly, the effect of human activities on them. Because weeds are a consequence of how we grow food, the study of both ecological and human components of agroecosystems should allow weed scientists to construct management strategies that more fully address the production, environmental, and social implications of weeds and weeding.

Author' note: This article is based on remarks made in February 1998 at the annual meeting of the Weed Science Society of America in Chicago. Those remarks were in turn based on an article, to be published in Spanish, titled “Es Antinatural la Manipulación Genética de los Animales?” The Spanish version will appear in the Proceedings of the Segundo Congreso Caribeno de Bioetica, University of Puerto Rico, Mayaguez, March 1998. It addresses the question of the engineering of animals; the focus here is the engineering of plants. Whether one considers flora or fauna, the unnaturalness objection raises the same cluster of concerns. Consequently, an assessment of those concerns need not vary significantly in turning from animals to plants.

Field experiments were conducted on eight weed species to determine if chlorimuron, fomesafen, imazethapyr, or sulfentrazone at two rates (labeled and one-half the labeled rate) were complementary tank mixtures with glyphosate at 210 and 420 g ai ha−1. Laboratory experiments were conducted on barnyardgrass, pitted morningglory, Palmer amaranth, and velvetleaf using radiolabeled glyphosate, chlorimuron, and imazethapyr to determine the absorption and translocation pattern of these herbicides applied alone and in combination. In the field, glyphosate plus chlorimuron tank mixtures were generally additive. Adding chlorimuron did not decrease absorption or translocation of 14C-glyphosate by barnyardgrass, pitted morningglory, or velvetleaf. Adding glyphosate increased absorption of 14C-chlorimuron by Palmer amaranth and velvetleaf. All four fomesafen plus glyphosate rate combinations were antagonistic to goosegrass, sicklepod, Palmer amaranth, and velvetleaf, and three of the four were antagonistic to barnyardgrass and entireleaf morningglory. Fomesafen decreased absorption and translocation of 14C-glyphosate in barnyardgrass, pitted morningglory, and velvetleaf. Ninety percent of glyphosate plus imazethapyr combinations were additive or synergistic, with all rate combinations synergistic for pitted morningglory. Adding glyphosate to imazethapyr increased absorption of 14C-imazethapyr by Palmer amaranth and velvetleaf. Glyphosate plus sulfentrazone tank mixtures were antagonistic at all rate combinations for barnyardgrass and Palmer amaranth and at three of the four combinations for goosegrass and entireleaf morningglory, indicating that these herbicides are not complementary in tank mixtures.

Greenhouse and field experiments were conducted to determine the effects of nitrogen (N) supply and purple nutsedge population densities on the yield of radish. In the greenhouse studies, additive series with purple nutsedge densities of 0, 50, 100, 200 or 350 plants m−2 were established. Nitrogen rates of 0, 110, 220, or 330 kg ha−1 were provided to the potting medium. A significant density by N interaction was found for radish fresh weight. Within a given nutsedge density, radish yield decreased as N rate increased. In field studies, additive series of 0, 50, 100, 150, or 200 nutsedge plants m−2 were established the same day radish was sown. Nitrogen rates were 100 or 200 kg ha−1. Marketable radish yield losses and nutsedge shoot dry weight and height were determined 30 d after seeding the crop. Nutsedge densities and N rates interactively influenced radish root yield. Radish yield loss reached 100% at nutsedge densities of 75 and 125 plants m−2 at 200 and 100 kg N ha−1, respectively. Purple nutsedge produced larger shoot biomass as N increased from 100 to 200 kg ha−1. Results of both greenhouse and field studies showed that as N increased, the negative effect of the weed on the crop was enhanced.

Field studies were conducted at two locations near Manhattan, KS, in 1994 and 1995 to determine the influence of density (0.5, 1, 2, 4, and 12 plants m−1 row) and time of emergence on redroot pigweed growth in monoculture or with sorghum. Redroot pigweed was seeded at sorghum planting and at the three- to four-leaf stage of sorghum in plots with sorghum or alone. When redroot pigweed grew with sorghum, dry matter and seed production were reduced with later times of emergence. In monoculture, there was no reduction in dry matter or seed number between the emergence dates studied. Redroot pigweed dry matter and seed production per plant were reduced as plant density increased for plants grown in monoculture. The same trend was observed for redroot pigweed grown with sorghum that did not emerge early relative to sorghum. Plants grown at low density exhibited more lateral growth than when grown at higher densities because of intraspecific competition.

We constructed a mechanistic model of purple nutsedge tuber population dynamics to provide a theoretical framework for the integrated management of this weed. The model relies on a transition matrix with 10 age classes to simulate fluctuations in the tuber population. Parameters of the transition matrix are given by functions of density, age, and cumulated incident photosynthetically active radiation (PAR) underneath crop canopies. Sensitivity ratios based on a 10% reduction in parameter values indicated that the parameters of the birthrate function were most sensitive. Simulations showed that in the absence of weed control, cumulated incident PAR was by far the strongest determinant of population size; intraspecific interference was the strongest determinant of the rate of population increase. When weed control was introduced, the simulation suggested that 95% control would be required to eliminate this weed. The analysis of simulation results led to the formulation of five research hypotheses of practical relevance to the management of purple nutsedge. New insights gained by testing these hypotheses should lead to practical recommendations as well as a better understanding of the relationships between management practices and fluctuations in purple nutsedge populations.

Formulations of Fusarium oxysporum Schlechtend:Fr. f.sp. erythroxyli isolate EN-4, pathogenic to Erythroxylum coca var. coca (coca) were evaluated in greenhouse and field studies to determine their relative ability to enhance pathogen populations in the soil or cause disease in coca. The formulations rice-alginate prill, Pesta, and C6 were most thoroughly tested and are products of three formulation processes. The formulations were applied in the greenhouse and field at 33.6 kg ha−1. All the formulations tested enhanced the population of EN-4 in the soil during greenhouse (> 6 wk) and field (> 7 mo) experiments. EN-4 was present in the upper 1 cm of formulation-treated soil at > 200-fold higher populations than established below a depth of 7 to 10 cm in both greenhouse and field experiments. This population distribution was maintained throughout the 7-mo sampling period for field experiments. The enhanced soil populations of EN-4 were associated with an increase in root colonization by the pathogen EN-4 in the field 5 to 7 mo after treatment. The formulated F. oxysporum began to have a significant effect on plant death 100 to 200 d after application in two of three field experiments, based on repeated measures analysis. The various formulations tested tended to establish similar pathogen populations in soil and subsequently caused similar levels of disease. The primary factors influencing formulation performance may be environmental, since inoculum production is dependent on sporulation of the formulation, which, although rapid, may continue over several weeks subsequent to application.

The preemergence efficacy of soil surface applications of a Phomopsis convolvulus granular formulation to control field bindweed seedlings was compared with its efficacy when inoculum granules were incorporated in soil. In addition, the effect of different doses of soil-applied granules was also determined. Under controlled environment conditions, incorporation of the fungal granules resulted in aboveground biomass reductions between 88 and 96%, with no significant differences observed between incorporation depths of 1.5 and 3 cm. Granule applications on the soil surface were less effective, reducing aboveground biomass 40 to 83%. In a parallel field experiment conducted over two growing seasons, however, surface applications of inoculum granules resulted in greater weed control compared with soil incorporation of the granules. In spring and summer trials conducted in 1996, surface applications resulted in a 93 and 100% aboveground biomass reduction, respectively, whereas incorporated granules reduced biomass 62 and 97%. Similar trends were observed in 1997. Different soil-applied doses of P. convolvulus did not affect the level of weed control under both controlled environment and field conditions. In 1995 and 1996 field trials, all rates used (30, 20, and 10 g 0.25m−2plot) resulted in substantial (90 to 100%) field bindweed aboveground biomass reductions. Findings in this study indicate that under field conditions, preemergence applications of the bioherbicide P. convolvulus on the soil surface provide effective control of field bindweed.

Field studies were conducted from 1995 to 1997 near Tifton, GA, to determine the benefits of stale seedbed weed control in cucumber. Three stale seedbed management systems—(1) power till stale seedbeds twice (2 ×), (2) glyphosate application immediately after planting, and (3) combination system of stale seedbeds power tilled once 2 wk prior to planting followed by glyphosate application immediately after planting cucumber—were evaluated as main plots. Subplots were weed management systems after planting cucumber: intensive, basic, and cultivation alone. Weed densities were generally greater in 1996 and 1997 than in 1995. Yellow nutsedge was the overall predominant species in 1995 (46 plants m−2), with Florida pusley being the predominant species in 1996 and 1997, at 80 and 124 plants m−2, respectively. Generally, stale seedbeds shallow tilled 2 × had fewer weeds and greater cucumber yields than stale seedbeds treated with glyphosate. Glyphosate did not adequately control emerged Florida pusley on stale seedbeds, resulting in reduced cucumber yield. Clomazone preemergence and bentazon/halosulfuron postemergence were used for broadleaf weed control in the intensive weed management system. These herbicides injured cucumber plants, delayed maturity, and reduced yield. Based on our results, stale seedbeds shallow tilled 2 × can be integrated into cucumber production and provide effective cultural weed control. Furthermore, these systems will replace the need for potentially injurious herbicides.

An accurate method is described for evaluating the relative effectiveness of isolates of Fusarium avenaceum as potential biological control agents for weeds such as spotted knapweed and wild oat. The method uses seeds that have been disinfected, placed in tubes containing water agar, and challenged with various isolates of F. avenaceum. Evaluatory data on the pathogenicity of the fungi are obtained after 14 d, when plants and fungi both are grown on water agar in the lab. Commonly, potential biocontrol agents are tested on seeds placed in the soil, but up to 60 d may be required for results. However, comparative studies using the soil test vs. the water agar test indicated that the water agar tests are giving comparable results to those from greenhouse tests but in a shorter time (14 vs. 60 d). Also, both water agar and soil tests were done with a number of crop plants including wheat, barley, alfalfa, and wild oat with comparable results. Thus, this method has the potential to screen many pathogens that may have potential biocontrol activities in a short time.

Substituted quinolinecarboxylic acids, including quinclorac (BAS 514H), are a new class of highly selective auxin herbicides, which are chemically similar to naturally occurring compounds isolated from plants and soils. Quinclorac is used in rice to control important dicot and monocot weeds, particularly barnyardgrass. The herbicide has also been developed for application in turfgrass areas, spring wheat, and chemical fallow. Quinclorac is readily absorbed by germinating seeds, roots, and leaves and is translocated in the plant both acropetally and basipetally. By mimicking an auxin overdose, quinclorac affects the phytohormonal system in sensitive plants. The compound stimulates the induction of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity and thus promotes ethylene biosynthesis. In susceptible dicots, increased levels of ethylene trigger an accumulation of abscisic acid (ABA), which, as part of the intrinsic auxin activity of quinclorac, plays a major role in growth inhibition and the induction of epinasty and senescence. In sensitive grasses, such as barnyardgrass species, large crabgrass, broadleaf signalgrass, and green foxtail, quinclorac leads particularly to an accumulation of tissue cyanide, formed as a co-product during increased ACC and ethylene synthesis. This causes phytotoxicity characterized by the inhibition of root and particularly shoot growth with tissue chlorosis and subsequent necrosis. These effects were not observed in tolerant rice and a resistant biotype of barnyardgrass. No significant differences in uptake, translocation, or metabolism of quinclorac between resistant and sensitive grasses were found. Hence, a target-site-based mechanism of selectivity is suggested. The induction process of the ACC synthase activity plays the primary role in the selective herbicide action of quinclorac. This is a common effect of auxin herbicides and auxins, which lead to the accumulation of cyanide and/or ABA depending on the plant species and tissues, the compound concentration in the tissue, and their biological activity.

Current weed demography models were reviewed to evaluate how the effects of cultural practices on weed dynamics were integrated into the models and to suggest possible ways to improve the simulation of cropping system effects. Several models were chosen to illustrate the interactions between cropping systems and weed dynamics. The first one described the structure of the weed life cycle. The second model integrated the effects of a wide set of cultural practices; the comparison of this example with other models suggested how the integration of cropping system effects could be improved. The last two models introduced the interactions of cultural practices with intraplot weed variability, either spatial variability of weed densities or genetic and phenotypic variability within weed populations. This review indicates some ways to make weed population models more comprehensive, robust, and accurate in order to improve their contribution to the evaluation and management of cropping systems.