The limited understanding of soil nitrogen (N) effects on crop yield loss to weeds prevents the refinement of integrated weed management to consider soil fertility. A 3-yr field experiment compared ammonium nitrate applications before corn emergence (PRE N) or in late June (POST N) on the growth of giant foxtail, velvetleaf, common waterhemp, and grain corn. The N responses were studied in corn population densities of 5.4 and 7.9 plants m−2 to understand how crop density might influence N effects on yield loss. In late June of each year, leaf areas were 25% (corn), 64% (velvetleaf), and 41% (giant foxtail) lower with POST N than with PRE N. Common waterhemp leaf area in late June was unaffected by N timing. Corn population density did not affect weed shoot dry weights evaluated in late June. Corn and velvetleaf heights in late July were up to 19 and 48% lower, respectively, with POST N compared with PRE N. Common waterhemp and giant foxtail heights in late July were unaffected by N timing. Corn yield was decreased 13 to 18% by giant foxtail with POST N compared with PRE N. Velvetleaf seed yield was lower, but giant foxtail seed yield was higher, with POST N than with PRE N. Velvetleaf and giant foxtail seed yields were 23 to 56% and 30 to 62% lower, respectively, with the high corn population density compared with the low population density. In competition between corn and common waterhemp, neither N timing nor corn population affected corn yield loss or common waterhemp seed production. N management may alter weed competitiveness and weed seed production in corn, but fertilization recommendations may vary with the weed species that are present.

The need for coordinated regional and global electronic databases to assist prevention, early detection, rapid response, and control of biological invasions is well accepted. The Pacific Basin Information Node (PBIN), a node of the National Biological Information Infrastructure, has been increasingly engaged in the invasive species enterprise since its establishment in 2001. Since this time, PBIN has sought to support frontline efforts at combating invasions, through working with stakeholders in conservation, agriculture, forestry, health, and commerce to support joint information needs. Although initial emphasis has been on Hawaii, cooperative work with other Pacific islands and countries of the Pacific Rim is already underway and planned.

Flucarbazone-sodium, a new herbicide, exhibits high bioactivity at low concentrations. To elucidate potential carryover and crop injury, the behavior of flucarbazone in six Western Canadian soils was studied in the laboratory. A sensitive bioassay was developed for the detection of flucarbazone. Of five crops tested, oriental mustard showed the highest degree of root and shoot inhibition from the presence of flucarbazone in soil. Flucarbazone concentrations as low as 1 μg kg−1 were detected by the mustard root inhibition method. This bioassay was used to examine phytotoxicity and persistence of flucarbazone. Phytotoxicity was related to soil organic carbon content. Concentrations corresponding to 50% inhibition (I50 values) were estimated after fitting the data to a log-logistic model. I50 estimates ranged from 6.0 to 27.5 μg kg−1 for soils containing 1.1 to 4.3% organic carbon, respectively, and were correlated (R = 0.979) with percent organic carbon in the investigated soils. Persistence of flucarbazone was examined in soils incubated at 25 C and moisture content of 85% field capacity (FC). Flucarbazone dissipation followed first-order kinetics in one soil, but a two-compartment model provided the best fit for dissipation in the other soils. Half-lives (t0.5), calculated from dissipation curves in each soil, ranged from 6 to 110 d. Half-lives were correlated (R = 0.776) with soil organic carbon. Flucarbazone dissipation was more rapid in soils containing less organic carbon. Flucarbazone was more persistent in drier soil; t0.5 was 11 d in soil at 85% FC and was 25 d in soil at 50% FC. Soil characteristics and environmental conditions will affect the degree of plant injury to sensitive crops the year after flucarbazone application.

The need for long-term agricultural research is generally recognized. However, most long-term experiments have been designed to evaluate effects of fertility and crop rotation. Much of the current research in weed biology and weed management is conducted on a short-term basis that does not address adequately the long-term aspects of weed population ecology. In recent decades, a number of long-term experiments have been initiated to investigate the effects of both agronomic and weed management practices on weed communities. Knowledge of the existence of these experiments and the information being obtained from them are not always readily available. The Symposium held at the 2002 WSSA annual meeting in Reno, Nevada, had several goals: (1) to provide WSSA members, and other researchers, with information about long-term experiments that are currently ongoing, or recently terminated, that are investigating weed ecology and weed management; (2) to provide an exchange of ideas between researchers involved in long-term weed ecology research; (3) to provide examples of protocols and problems associated with conducting long-term weed ecology research; (4) to evaluate the scientific principles that have been, or may be, added to the discipline of weed science; and (5) to provide funding agencies with examples of how long-term weed management experiments clarify impacts of weeds in relation to sustainable agriculture.

The Broadbalk experiment was started in 1843 to investigate the relative importance of different plant nutrients (N, P, K, Na, Mg) on grain yield of winter wheat. Weeds were controlled initially by hand hoeing and fallowing, but since 1964, herbicides have been applied to the whole experiment with the exception of the 18 plots on Section 8. Approximately 130 weed species have been recorded on Broadbalk and about 30 of these are currently recorded annually on Section 8. Detailed weed surveys, conducted from 1930 to 1979, provide a unique 50-yr record, but the relatively small number of frequency categories used (six) poses a limitation on the interpretation of these data for ecological studies. Weed surveys were restarted in 1991 on Section 8. The current assessment method records the presence of individual weed species in 25 random 0.1-m2 quadrats per plot, which is more appropriate for detecting long-term trends in weed frequencies and population differences between plots. A principal components analysis of the 1991–2002 survey data for 15 species showed clearly the influence of inorganic N fertilizer levels on the frequency of individual species. The frequency of one species (common chickweed) was greatly favored by increasing amounts of nitrogen fertilizer from 0 to 288 kg N ha−1, others were strongly disadvantaged (e.g., black medic and field horsetail), some were slightly disadvantaged (e.g., common vetch and parsley-piert), and some showed little response to differing N rates (e.g., blackgrass and corn poppy). Other weed investigations include studies on the effects of fallowing on the weed seed bank, seed dormancy and persistence, agroecology, and population dynamics of individual weed species. Recently, molecular approaches have been used to study the genetic diversity of weeds found on Section 8, which is one of the few arable sites in the country where herbicides have never been applied. This site also provides an invaluable reserve for seven nationally rare or uncommon species. Broadbalk continues to act as a valuable resource for weed investigations 160 yr after it was established.

Production systems based on reduced-tillage practices account for over 60% of the cropped land on the Canadian Prairies. Concerns have been expressed regarding potential shifts in weed communities as a result of changing tillage practices. Study objectives were to (1) determine the feasibility of combining and analyzing weed abundance data from 10 medium- to long-term studies on the Canadian Prairies that compared conventional-, reduced-, and zero-tillage systems, (2) identify species that are associated with specific tillage systems, and (3) place species into plant response groups according to the similarity of their tillage system response. Conventional-tillage systems were defined as including both a fall and spring sweep-plow operation before seeding spring crops, whereas reduced tillage consisted of only one sweep-plow operation shortly before seeding. Crops within zero-tillage systems were planted directly into the previous crop's stubble. The association between weed species and tillage systems was investigated using indicator species analysis. Species were assigned to tillage response groups on the basis of the results of the analysis and the expertise of the project scientists. Perennial species such as Canada thistle and perennial sowthistle were associated with reduced- and zero-tillage systems, but annual species were associated with a range of tillage systems. Field pennycress was placed in the conventional-tillage response group, Russian thistle in the zero-tillage group, and wild buckwheat and common lambsquarters were equally abundant in all tillage systems. The goal of classifying weed species based on common functional traits in relation to responses to tillage systems was not realized, in part, because the required information on species biology and ecology was either unavailable or not applicable to local conditions.

The main study objective was to measure the effects of tillage (moldboard plow, chisel plow, and no-till) and weed management (intensive, moderate, and minimum) on weeds and crops in a spring barley monoculture compared with a spring barley–red clover rotation. The study was initiated in 1987 and conducted at two sites. Residual effects of treatments were measured in a wheat test crop at the loam site in 1994 and at the clay site in 1995–1996. Weed seed bank densities ranged from less than 300 to nearly 30,000 seeds m−2 and plant densities from 30 to 6,000 plants m−2. Seven species were recorded on average per plot aboveground and 10 species per plot in the seed bank. Species number in the seed bank varied little with treatments compared with species numbers aboveground. Crop rotation and tillage had little effect on weed species diversity but affected relative species dominance. The presence and abundance of species was also influenced by their degree of tolerance to the herbicides used in each system. Annual dicots largely dominated in minimum weed management treatments. Their relative importance in each rotation varied with their level of susceptibility to the different postemergence herbicides. Perennials were not exclusively found in reduced tillage systems. The relationship between perennials and tillage was dependent on the response of perennating structures to the type and frequency of soil disturbance. For example, quackgrass dominated in chisel and moldboard plow systems where rhizomes would be frequently fragmented. Field horsetail, also a rhizomatous species, dominated in the monoculture/direct-seeded no-till treatment under minimum weed management. Its absence from the rotation was explained by the regular removal of aboveground biomass during the forage production year. Overall, weed response was regulated by agronomic factors but was largely determined by specific biological attributes and environmental conditions.

A 6-yr project comparing four cash grain–farming systems relevant to the mid-Atlantic region of the United States was conducted from 1993 to 1999. A wide range of parameters was sampled including soil health, nutrient and agrichemical movement, economic viability, and insect and weed communities. The systems and their approaches to weed management were: continuous no-till corn without (System A1) or with (System A2) rye cover crop and preplanned herbicides based on expected weed infestations; System B was a 2-yr corn–soybean rotation with conventionally tilled corn and no-tillage soybean, with preplanned herbicides based on expected weed infestations; System C was a 2-yr rotation with no-till corn, conventionally tilled wheat, and no-till double-cropped soybean, using postemergence (POST) herbicides on the basis of field scouting; and System D was a 3-yr rotation of corn-soybean-winter wheat with rye and hairy vetch cover crops, using cultivation and reduced rates of POST herbicides based on field scouting. Spring weed assessment in 1999 was similar for species evenness (Shannon's E) and diversity (Shannon's H′) indices. Weed density was lowest in System C because wheat in this system received a spring herbicide application. In the final fall assessment, Shannon's H′ was greater in System D than System C. Common lambsquarters, eastern black nightshade, and jimsonweed were more abundant in System D than Systems A1, A2, and C. Fall 1999 assessment also indicated Canada thistle was more prevalent in Systems A1 and A2 than the other three systems. During the 6-yr period, densities of jimsonweed, eastern black nightshade, morningglory species, crabgrass, and fall panicum dramatically increased in a particular system for 1 to 2 yr, then declined to levels similar to other systems. Overall, weed communities were quite stable and effective weed management did not result in dramatic changes in the weed community, regardless of the approach to cropping systems or weed management.

The winter wheat production system of the Pacific Northwest is characterized by severe wind and water erosion and winter annual grass weeds requiring high herbicide input. Since 1985, numerous multi- and interdisciplinary, long-term, large-scale, integrated cropping systems studies have been or are currently being conducted. The primary focus of these studies was on weed biology, ecology, and management, whereas secondary evaluations were on alternative cropping systems, conservation tillage, and fertilizer or herbicide inputs. The 6-yr integrated pest management project, conducted in the high-rainfall zone (> 400 mm), showed for the first time that when weeds were adequately managed, conservation production systems were more profitable than conventional systems. In the intermediate rainfall zone (350 to 400 mm), a recently concluded 6-yr, three-state study integrated single-component research results into a multifaceted approach to managing jointed goatgrass. This project has been used as a model study for other western states and the National Jointed Goatgrass Research Initiative. At present (9 yr thus far), a study is being conducted in the low-rainfall zone (< 350 mm) to examine the feasibility of no-till spring cropping systems in lieu of the highly erosive, weed infested, wheat–fallow system. Because of these projects, the Washington Wheat Commission recognized the importance of long-term, interdisciplinary, cropping systems research and has therefore established an Endowed Chair at Washington State University for direct seed cropping systems research. Federal, national, and regional agencies have used information from these projects for farm plans and pesticide usage.