Weed scientists face complex and difficult challenges. Within our discipline, we must increase the sustainability of current weed management approaches and help respond to invasive plants as a component of global change. There also are major challenges that we share with other agricultural disciplines, such as mounting comprehensive efforts to address the problems of current agriculture. We believe that any effective response to these challenges will require public work, i.e., projects in which a diverse group of people work together—across lines of difference (professional, cultural, etc.)—to produce broad-based, systemic innovations that meet complex challenges. We propose that weed scientists should join relevant public-work projects by practicing “public scholarship.” We define public scholarship as original, creative, peer-evaluated intellectual work that is fully integrated in a public-work project. By full integration we mean that the scholar's work serves to fuel the social (i.e., collective) learning of the public-work group. This condition requires that the scholar be a full participant in the group rather than just being in a consultative or advisory role. We present several case studies of weed scientists practicing public scholarship. These scientists found this mode of scholarship to be a highly effective means by which to address their professional priorities. Barriers to the practice of public scholarship include the lack of relevant guidelines and norms within academic culture, e.g., with regard to quality-assurance standards. But public scholarship offers weed scientists a new way of responding to increasingly urgent demands to show that our work effectively produces public value in return for public investment. We believe that graduate programs in weed science should begin to offer students opportunities to learn skills that are relevant to public scholarship.

The use of scouting and economic thresholds has not been accepted as readily for managing weeds as it has been for insects, but the economic threshold concept is the basis of most weed management decision models available to growers. A World Wide Web survey was conducted to investigate perceptions of weed science professionals regarding the value of these models. Over half of the 56 respondents were involved in model development or support, and 82% thought that decision models could be beneficial for managing weeds, although more as educational rather than as decision-making tools. Some respondents indicated that models are too simple because they do not include all factors that influence weed competition or all issues a grower considers when deciding how to manage weeds. Others stated that models are too complex because many users do not have time to obtain and enter the required information or are not necessary because growers use a zero threshold or because skilled decision makers can make better and quicker recommendations. Our view is that economic threshold–based models are, and will continue to be, valuable as a means of providing growers with the knowledge and experience of many experts for field-specific decisions. Weed management decision models must be evaluated from three perspectives: biological accuracy, quality of recommendations, and ease of use. Scientists developing and supporting decision models may have hindered wide-scale acceptance by overemphasizing the capacity to determine economic thresholds, and they need to explain more clearly to potential users the tasks for which models are and are not suitable. Future use depends on finding cost-effective methods to assess weed populations, demonstrating that models use results in better decision making, and finding stable, long-term funding for maintenance and support. New technologies, including herbicide-resistant crops, will likely increase rather than decrease the need for decision support.

Despite several decades of modern weed control practices, weeds continue to be a constant threat to agricultural productivity. Herbicide-resistant weeds and weed population shifts continue to generate new challenges for agriculture. Because of weed community complexity, integrated approaches to weed management may help reduce economic effects and improve weed control practices. Integrated weed management emphasizes the combination of management techniques and scientific knowledge in a manner that considers the causes of weed problems rather than reacts to existing weed populations. The goal of weed management is the integration of the best options and tools to make cropping systems unfavorable for weeds and to minimize the effect of weeds that survive. No single practice should be considered as more than a portion of an integrated weed management strategy. The best approach may be to integrate cropping system design and weed control strategies into a comprehensive system that is environmentally and economically viable. Management decisions must also be made on a site- and time-specific basis. Considering weeds in a broader ecological and management context may lead to the use of a wider range of cultural and management practices to regulate weed communities and prevent the buildup of adapted species. This will help producers manage herbicides and other inputs in a manner that preserves their effectiveness and move weed scientists toward the development of more diverse and integrated approaches to weed management.

Cover crops and living mulches bring many benefits to crop production. Interest in winter annual cover crops such as winter rye and hairy vetch for ground cover and soil erosion control has been increasing in the last 30 yr in some areas. The integration of cover crops into a cropping system by relay cropping, overseeding, interseeding, and double cropping may serve to provide and conserve nitrogen for grain crops, reduce soil erosion, reduce weed pressure, and increase soil organic matter content (Hartwig and Hoffman 1975). Hairy vetch has increased availability of nitrogen to succeeding crops, increased soil organic matter, improved soil structure and water infiltration, decreased water runoff, reduced surface soil temperature and water evaporation, improved weed control, and increased soil productivity (Frye et al. 1988). More recent research with perennial living mulches, such as crownvetch (Hartwig 1983), flatpea, birdsfoot trefoil, and white clover (Ammon et al. 1995), has added a new dimension to the use of ground covers that eliminates the need to reseed each year. Cropping systems with the use of ground covers have been worked out for vineyards, orchards, and common agronomic crops, such as corn, small grains, and forages. Legume cover crops have the potential for fixing nitrogen, a portion of which will be available for high-nitrogen–requiring crops such as corn. In areas where excess nitrogen is already a problem, the use of ground covers may provide a sink to tie up some of this excess nitrogen and hold it until the next growing season, when a crop that can make use of it might be planted (Hooda et al. 1998). Even legumes tend to use soil nitrogen rather than fixing their own, if it is available. It is these possibilities that provide the incentive for looking at the effect of various kinds of cover crops on soil erosion, nitrogen budgets, weed control, and other pest management and environmental problems.

Laboratory and greenhouse experiments were conducted to determine the herbicidal effect of plant-derived oils and to identify the active ingredient in an oil with herbicide activity. Twenty-five different oils were applied to detached leaves of dandelion in the laboratory. Essential oils (1%, v/v) from red thyme, summer savory, cinnamon, and clove were the most phytotoxic and caused electrolyte leakage resulting in cell death. Each of these essential oils in aqueous concentrations from 5 to 10% (v/v) plus two adjuvants (nonionic surfactant and paraffinic oil blend at 0.2% [v/v]) were applied to shoots of common lambsquarters, common ragweed, and johnsongrass in the greenhouse; shoot death occurred within 1 h to 1 d after application. Essential oil of cinnamon had high herbicidal activity, and eugenol (2-methoxy-4-[2-propenyl]phenol) was determined to be this oil's major component (84%, v/v). Dandelion leaf disk and whole-plant assays verified that eugenol was the active ingredient in the essential oil of cinnamon. Essential oils are extracted from plants and thus may be useful as “natural product herbicides” for organic farming systems.

Green algal cell suspensions are used in agrochemical research for screening herbicides. This paper reports on the inhibitory effects of 39 herbicides from 19 different chemical classes with nine different modes of action on green algae cultured in liquid media. The results show that herbicide screening using Chlorella as a model organism is simple, quick, and sensitive. In vitro systems can be a second screening net to ensure that potential new structures are not missed. A set of biotests using cell suspension cultures of Chlorella are suggested as a herbicide prescreen to eliminate inactive compounds before testing on higher plants in the greenhouse. The method has been shown to be suitable for the requirements of microscreen and high-throughput screening (HTS) in vitro. A large-scale microscreen has been devised, which cultures algal cells using self-made Erlenmeyer flasks containing 5 ml of liquid medium. They are particularly useful for HTS compounds with dissimilar modes of action.

Natural products represent a vast repository of materials and compounds with evolved biological activity, including phytotoxicity. Some of these compounds can be used directly or as templates for herbicides. The molecular target sites of these compounds are often unique. Strategies for the discovery of these materials and compounds are outlined. Numerous examples of individual phytotoxins and crude preparations with weed management potential are provided. An example of research to find a natural product solution of a unique pest management problem (blue-green algae in aquaculture) is described. Finally, the problems associated with natural products for pest control are discussed.

Data containing many variables are often collected in weed science research, but until recently few weed scientists have used multivariate statistical methods to examine such data. Multivariate analysis can be used for both descriptive and predictive modeling. This paper provides an intuitive geometric introduction to the more commonly used and relevant multivariate methods in weed science research, including ordination, discriminant analysis, and canonical analysis. These methods are illustrated using a simple artificial data set consisting of abundance measures of six weed species and two soil variables over 12 sample plots.

Community assembly is a branch of ecology that looks at how communities are assembled as they follow trajectories through time. A trajectory is controlled by biotic and abiotic constraints (filters) that act at multiple scales. From a total species pool, environmental and dispersal constraints control which species enter an ecological species pool. Within this pool, internal dynamics determine which of these species becomes part of the extant community. Environmental filters act by removing species that lack specific traits. Thus, traits are filtered, and with them, species. In this paper, we present the basic ecological theory of community assembly and address how it can be used in conjunction with a trait-based approach to understand and possibly predict how weed community structure changes in response to imposed filters such as tillage or crop rotation. Weed ecologists have struggled with the need to place our practical knowledge of agriculture and weeds into a broader theory, and there have been many calls to integrate ecology with agronomy and weed science. Community assembly might be one way to do so.

Laboratory and field experiments were conducted to determine the effects of several environmental factors on seed germination and seedling emergence of the invasive weed, apple of Peru. The anatomy of the seed was also investigated in this study. The anatomy of the seed is similar to that of an eggplant (Solanum melongena L.) seed. The seed is albuminous, and consists of a seed coat, endosperm, and an embryo. The seed coat, which consists of both outer and inner integuments, is relatively thick. Fresh and dry stored seeds exhibited strong dormancy. Hot water treatment did not affect the seed germination in the light, but significantly (P < 0.05) reduced the germination rate in the dark. Dry-heat treatment had no significant effect on seed germination in the dark, but it significantly (P < 0.05) increased the germination rate in the light. Cold stratification alone did not influence seed germination under constant temperature (25 C) but affected it under alternating temperature (25–15 C). However, a combination of warm and cold stratification produced significant (P < 0.05) germination in the dark as well as in the light. In addition, the effect of warm stratification followed by cold stratification was more pronounced in the dark than in the light. Gibberellin A3 (GA3) (10–3 and 10–4 M) treatments significantly (P < 0.05) increased the seed germination rate compared with that of the control. Emergence rate was maximum for seeds placed on the soil surfaces; no seedling emergence occurred when seeds were placed at a depth of 5 cm.

Herbicides that target the enzyme acetolactate synthase (ALS) are among the most widely used in the world. Unfortunately, these herbicides are also notorious for their ability to select resistant (R) weed populations. Now, there are more weed species that are resistant to ALS-inhibiting herbicides than to any other herbicide group. In most cases, resistance to ALS-inhibiting herbicides is caused by an altered ALS enzyme. The frequent occurrence of weed populations resistant to ALS inhibitors can be attributed to the widespread usage of these herbicides, how they have been used, the strong selection pressure they exert, and the resistance mechanism. In several cropping systems, ALS-inhibiting herbicides were used repeatedly as the primary mechanism of weed control. These herbicides exert strong selection pressure because of their high activity on sensitive biotypes at the rates used and because of their soil residual activity. Several point mutations within the gene encoding ALS can result in a herbicide-resistant ALS. From investigations of numerous R weed biotypes, five conserved amino acids have been identified in ALS that, on substitution, can confer resistance to ALS inhibitors. Substitutions of at least 12 additional ALS amino acids can also confer herbicide resistance in plants and other organisms but, to date, have not been found in R weed populations. Mutations in ALS conferring herbicide resistance are at least partially dominant, and because the gene is nuclear inherited, it is transmitted by both seed and pollen. Furthermore, in many cases there is apparently a negligible fitness cost of the resistance gene in the absence of herbicide selection. Although resistance to ALS-inhibiting herbicides has been a bane to weed management, it has spurred many advances within and beyond the weed science discipline. As examples, resistance to ALS-inhibiting herbicides has been exploited in the development of herbicide-resistant crops, studies of weed population dynamics, and in developing protocols for targeted gene modification. Resistance to ALS-inhibiting herbicides has greatly affected weed science by influencing how we view the sustainability of our weed management practices, what we consider when developing and marketing new herbicides, and how we train new weed scientists.

Glufosinate efficacy was examined in two major grass weed species, rigid ryegrass and sterile oat. Dose–response pot experiments under controlled environmental conditions showed that sterile oat was more successfully controlled by glufosinate than was rigid ryegrass. Glutamine synthetase was extracted from both species and assayed in vitro. Glufosinate readily inhibited glutamine synthetase activity in both species, indicating no differential sensitivity to the target enzyme. Thin-layer chromatography analysis of glufosinate showed no significant metabolism of glufosinate in either species. Absorption and translocation studies with 14C-glufosinate showed that the radiolabel was rapidly absorbed into the leaves of both species. However, translocation of radiolabeled glufosinate from the treated leaf to the meristematic regions was significantly greater in sterile oat, whereas translocation to the tip of the leaf was significantly greater in rigid ryegrass. This indicates that there is a difference in glufosinate distribution between the two species. It is likely that this difference in the distribution of glufosinate results in sterile oat being more easily controlled by glufosinate than is rigid ryegrass.

Studies were conducted to evaluate absorption, translocation, and metabolism of 14C-CGA 362622 when foliar applied to cotton, peanut, jimsonweed, and sicklepod. Differential metabolism is the basis for tolerance in cotton and jimsonweed. In addition, cotton absorbs less herbicide compared with the other three species, thus aiding in tolerance. Only jimsonweed translocated appreciable herbicide (25%) out of treated leaves and acropetally to the meristematic tissue where the herbicide was quickly metabolized. No plant species translocated over 2% of applied radioactivity below the treated leaves. Most of the metabolites formed by the four species were more polar than CGA 362622 and averaged 51, 48, 30, and 25% of the radioactivity detected in the treated leaves of cotton, jimsonweed, peanut, and sicklepod, respectively. The half-life of CGA 362622 was estimated to be 0.8, 1.9, 4, and 6 d in treated leaves of cotton, jimsonweed, sicklepod, and peanut, respectively.

This paper is a review of and a commentary on the published addresses of WSSA presidents from the founding of the Society through 2000. The paper's assumptions are that the presidential remarks will reveal what the Society has emphasized, what its major concerns and goals have been, and how the presidents have addressed what they considered to be important issues. Seven issues have been addressed by many presidents. These include the importance of agricultural production and profit, the necessity of herbicides, weed science and the environment, the regulation of herbicides, the need for education, comparison of weed science and other plant protection disciplines, and the problem of herbicide resistance.

In 1996 a common sunflower population near Howard, SD, was suspected to be cross-resistant to imazethapyr and chlorimuron. Whole-plant acetolactate synthase (ALS) assays confirmed ALS-inhibitor resistance in the Howard biotype. The I50 values (inhibition of 50% of the enzyme activity) indicated that the resistant population required 39 and 9 times more imazethapyr and chlorimuron, respectively, to obtain the same level of enzyme inhibition compared with the sensitive biotype. Herbicide dose response data supported the whole-plant enzyme assay data; control (> 90%) was not achieved with less than a four-times application rate of chlorimuron. Control with imazethapyr was not achieved even with a 16-times rate. Chlorimuron and imazethapyr controlled 70 and 95% of the population, respectively, when a four-times rate of each herbicide was applied separately. Differences in 14C-herbicide absorption were observed, suggesting that there may be physical or chemical differences in leaf surface composition between the resistant and sensitive biotypes. Although translocation of 14C-herbicide was less in the resistant biotype than in the sensitive biotype, the differences were not enough to explain chlorimuron and imazethapyr selectivity between the two biotypes. Overall results suggested that the differences in the common sunflower populations were attributed to an altered site of action on the ALS enzyme.

A population of giant ragweed not controlled by cloransulam was identified near Seymour, IN, during the first year of that herbicide's commercialization in 1998. Results from acetolactate synthase (ALS) activity assays performed by Dow AgroSciences showed that resistance was caused by an altered ALS. Studies were conducted to define more precisely the molecular basis of resistance and to determine cross-resistance to other ALS-inhibiting herbicides. Sixteen greenhouse-grown giant ragweed plants from the Seymour population were tested individually with postemergence (POST) applications of cloransulam, imazethapyr, or chlorimuron, or by using a nondestructive leaf disk assay to determine resistant or sensitive herbicide responses. All plants identified from the Seymour population as resistant to cloransulam were cross-resistant to imazethapyr and chlorimuron. Two DNA fragments, totaling 804 nucleotide base pairs, within ALS were sequenced from each of the 16 plants. Sequence data, combined with phenotypic data, showed that a tryptophan to leucine substitution at amino acid position 574 of ALS (based on numbering of the Arabidopsis ALS) was responsible for ALS-inhibitor resistance. Among 11 resistant and 5 sensitive giant ragweed plants analyzed from the Seymour population, at least 15 different ALS alleles were identified. Of these 15 alleles, two alleles, at an average frequency of 0.25, contained a leucine at position 574 and conferred resistance. The 13 alleles that conferred susceptibility to ALS-inhibiting herbicides occurred at an average frequency of 0.04.

Field experiments were conducted from 1997 through 1999 to evaluate interspecific interference between pitted morningglory at 0, 10, 16, and 62 plants m−2 and drill-seeded, glyphosate-resistant soybean as influenced by soybean population and a single glyphosate application of 1.12 kg ai ha−1. Photosynthetic rate of soybean was not influenced by pitted morningglory density or glyphosate use 2 wk after treatment (WAT). Photosynthetic rate of soybean 12 WAT was reduced by 21 and 91% with 62 treated and untreated pitted morningglory plants m−2, respectively, whereas 10 treated and untreated pitted morningglory plants m−2 had no effect on the soybean photosynthetic rate. Pitted morningglory photosynthetic rate 2 and 12 WAT was reduced by 64 and 80%, respectively, when treated with glyphosate. The reduction in the photosynthetic rate of glyphosate-treated pitted morningglory was partially attributed to shading by soybean, whereas untreated plants were fully exposed to sunlight. Glyphosate-treated pitted morningglory at 10 and 16 plants m−2 did not reduce the rate of soybean leaf area index (LAI) accumulation; however, when the density was increased to 62 pitted morningglory plants m−2, soybean LAI decreased from 1.19 to 0.88 for each accumulated 100 growing degree days. Pitted morningglory produced a maximum of 24 million seeds ha−1 in the absence of glyphosate with 217,000 soybean plants ha−1. Pitted morningglory seed production declined with increasing soybean seeding rate in the absence of glyphosate, with a 41% reduction occurring when soybean population increased from 217,000 to 521,000 plants ha−1. Seed production of treated pitted morningglory ranged from 380,000 to 700,000 seeds ha−1. Soybean seed yield was not influenced by pitted morningglory density when treated with glyphosate. Untreated pitted morningglory at 10, 16, and 62 plants m−2 reduced soybean seed yield by 47, 62, and 81%, respectively. Competitiveness of untreated soybean increased with soybean seeding rate, resulting in 22% less yield loss with 521,000 than with 217,000 plants ha−1. Soybean seed yield was not reduced by 10 and 16 glyphosate-treated pitted morningglory plants m−2, but a 9% loss in yield occurred with 62 pitted morningglory plants m−2. Averaged over all pitted morningglory densities, glyphosate-treated pitted morningglory failed to reduce soybean seed yield at each of the three soybean densities. Following a single application of glyphosate, no apparent benefit was noted from increasing the soybean population above 217,000 plants ha−1.