Long term weed management programs for annual weeds should take into account seed production as well as yield losses from weeds. In this research economic optimum thresholds, determined with a simulation model, were compared to the economic thresholds derived from field studies with common sunflower and velvetleaf in soybean. An economic optimum threshold model, including a biological submodel and a submodel evaluating the financial benefit from controlling each weed species in soybean, was constructed to estimate the biological events and processes and economic costs of each weed. Long-term weed management programs were simulated in continuous soybean over a 15-yr period. The model optimized a POST treatment of bentazon by computing costs associated with weed interference and changes in estimated seedbank size. The economic optimum threshold populations were estimated to be 0.3 to 0.4 velvetleaf plants per 10 m2 and 0.4 common sunflower plants per 10 m2. The economic thresholds calculated to be 2.6 velvetleaf plants per 10 m2 and 1.5 common sunflower plants per 10 m2. The economic optimum threshold was calculated to be 7.5-fold and 3.6-fold lower than the economic thresholds for velvetleaf and common sunflower, respectively. The larger ratio for velvetleaf reflected the large quantity and longevity of seeds produced. The smaller ratio for common sunflower reflected the shorter persistence of the seeds and higher seed predation rates.

Collections of woolly morningglory from New Mexico were determined to be tall morningglory (Ipomoea purpurea) or, in some cases, ivyleaf morningglory (I. hederacea) by misapplication. Woolly morningglory is a variant of tall morningglory with lobed leaves known as I. purpurea var. diversifolia by some sources, although modern taxonomists consider this variant to be undeserving of variety rank.

The effect of weather variation on pesticide losses was estimated with the Erosion-Productivity Impact Calculator (EPIC) model. Weather variations had little effect on pesticide loss from a hypothetical site near Memphis, TN, but the effect was more dramatic and in the expected direction at Des Moines, IA. Atrazine losses at Des Moines were reduced by lowering relative humidity or rainfall intensity. Increasing the CO2 level from 300 to 660 ppm slightly increased atrazine losses. Results from these two sites are very limited and only serve to demonstrate modeling potential for addressing weather/pesticide problems. Further, more comprehensive studies are needed to better estimate pesticide loss sensitivity to weather variation.

Conventional strategies for developing component technologies are being challenged by the complexities of today's agricultural environment. The needs for support of adaptive research, for sufficient field sites to evaluate location specificity of technologies, and for testing components as parts of total farm systems are not easily met within the confines of the experiment station. On-farm research strategies involve the farmer and rancher in project design, field implementation, collection and evaluation of data, and interpretation of results. Farmer presentations in extension meetings and field tours involve these cooperators in the demonstration and technology sharing process. Farmers in Nebraska and Wisconsin have applied this process to research nitrogen levels in continuous and rotated cereals, the use of allelopathic chemicals from rye (Secale cereale L.) to reduce herbicide costs in soybean [Glycine max (L.) Merr.] production, on other alternative weed management strategies, and strip cropping to reduce soil erosion and meet government program compliance requirements. Useful in a wide range of ecological and economic circumstances, participatory methods using farming systems research and extension strategies have global applications.

Basic, applied, operational, and human activity research systems represent an array of inquiry methodologies. Techniques or methods within each methodology exhibit similar functions, although purposes and results of each inquiry process differ. Appreciation and possible use of the entire inquiry process focuses attention on scale questions within a hierarchy, and encourages use of all methodologies to enhance resolution of diverse situations. Systems inquiry recognizes the need for weed scientists and agriculturists to participate in activities ranging between reductionist science and human action research.

A screening procedure to minimize adverse water quality impacts of pesticide application is presented that matches pesticide parameters to site-specific soil ratings. The pesticide parameters include a Relative Leaching Potential Index (RLPI), a Relative Runoff Potential Index (RRPI), the U.S. Environ. Prot. Agency (USEPA) lifetime health advisory level (HAL), and aquatic toxicity (LC50). Criteria used in developing soil ratings are described. Pesticide selection is accomplished by matching pesticide parameters values for the array of pesticides that control the pest of interest to soil ratings at the application site using selection criteria. A worksheet is presented to facilitate organization of information for the selection procedure and to serve as a record of the pesticide applicator's decision. The linking of an environmental fate model to a geographic information system (GIS) to create thematic maps of pesticide leaching potentials in terms of probability of exceeding the HAL in groundwater is described. A cost vs. groundwater hazard index frontier is described that suggests a method to assess the economic consequences of alternative pesticide selections.

A mail survey was undertaken in 1991 to obtain information on beginning weed science courses being taught in the United States and Canada. Out of 74 questionnaires sent to 44 states and 7 provinces, there were 54 responses of which 49 institutions had a beginning weed science course. The responses showed that these courses are taught primarily once a year (88%) in the fall term (77%). Most schools are under the semester system (82%) with the credits arranged so that there are about 30 hours of lecture per term with a one-credit laboratory. The students in beginning weed science courses are mostly seniors (47%) and juniors (34%) and are primarily from Agronomy, Plant Science, or Crop Science departments (46%) and Horticulture (23%). The average time spent on different topics agreed well with the priorities and are listed in the text. The survey also gathered data on weed identification requirements, special requirements of individual courses, evaluation of students, additional comments by instructors, and special teaching guides or techniques that instructors are willing to share with others.

In support of the registration and reregistration processes under FIFRA ‘88, numerical models are used to estimate the dissolved runoff and soil erosion loadings of pesticides to surface waters and the subsequent fate and transport of pesticides in the receiving waters. Uses for simulations include:

1. Helping to determine whether additional studies on the fate and distribution of a candidate chemical in the environment and/or ecological effects may be needed when full chemical characterization is incomplete.

2. Helping to more fully integrate data submissions of laboratory and field observations.

3. Estimating probable fate and distribution of an agrochemical after a severe runoff event.

4. Comparing alternative chemical application rates and methods for the same chemical/soil/crop/environmental combinations.

5. Comparing different soil/crop/environmental combinations representing different geographical areas with the same chemical.

6. Evaluating preliminary designs of proposed field studies.

7. Gaining insight into the environmental fate of modern chemicals that are applied at 1 to 2% of the rates of older chemicals when sampling designs and analytical methods are not available.

The Office of Pesticide Programs (OPP) commonly employs the SWRRB (45, 46) and PRZM (8, 9) models for runoff and EXAMS II (5), a fate and transport model, for surface waters. These three models are used in conjunction with appropriate databases for soils, chemical properties, and meteorological and other environmental parameters. Registrants are encouraged to clearly state assumptions, identify values for parameters by citation, report results of simulations with summary tables and graphics, and interpret their results in relation to current scientific disciplines.

Itchgrass [Rottboellia cochinchinensis (Lour.) Clayton ♯ ROOEX] is a large aggressive annual in the Poaceae. This weedy grass is native to Southeast Asia. It now occurs also in tropical and subtropical areas of Australia and Africa and has been introduced into the West Indies and North, Central, and South America. It apparently was introduced into the United States at Miami, Fla. and Lafayette, La. in the early 1900s (1, 6, 7).

The ARS Pesticide Properties Database (PPD) is a compendium of chemical and physical properties of a collection of widely used pesticides. At present, there are 92 compounds in the database and we have focused on 19 of the most important properties impacting on groundwater and atmospheric quality. The PPD relies upon experimentally determined data points. With the help of the National Agricultural Chemicals Association (NACA) we have been communicating directly with manufacturers to obtain the original experimental data with which they characterize pesticide properties and fulfill requirements for federal and state regulations. This provides the basis for the PPD which is augmented with data from the scientific literature. Features of the PPD are: 1. 19 parameters are provided for each pesticide. 2. References are given for all data. 3. When there are several values for a given property, all are cited. 4. All data have been verified and provide the latest, most reliable figures available.

Nettles belong to the genus Urtica, in the Urticaceae, which includes about 30 species of herbs, shrubs, and trees of world-wide distribution (3, 12). These species have recognizable similarities but vary considerably in height - from 0.3 to 0.66 m to 2.6 or 3 m tall (15). Nettles have a peculiar notoriety. As the 17th century herbalist Nicholas Culpeper (5) wrote, “Nettles are so well known, that they need no description, they may be found by feeling for them in the darkest night.”

Registrant use of computer simulation modeling is generally accepted by regulators in lieu of some experimental data for risk assessment, provided worst-case assumptions and extremely conservative criteria for negligible risk are used. These requirements taken together mean that only extreme cases escape the requirement for actual environmental data. This conservatism reflects the uncertainty in both exposure estimates by the models and in the hazard estimates from toxicologists. Until the credibility of estimated environmental concentrations given by models is improved by more experimental data and experience on the part of both registrants and regulators, the models will continue to be considered not-validated by many. There are four current developments that provide a compromise between the two impossible extremes of total model validation and total field measurement: (1) as models develop more process detail the parameters become more fundamental in nature and these are generally more amenable to independent estimation or measurement; (2) the reporting of probabilistic analyses and probable errors of results by modelers will enhance credibility; (3) the development of data sets for specific crop/site/pesticide/weather scenarios will allow users to modify those parts of the input they are concerned with while retaining confidence that parameters with which they are unfamiliar will have reasonable values; and (4) meso-scale and micro-scale physical simulation experiments can fill the gap between laboratory and field results. The most important need for enhancing model credibility is full access by the pesticide science community to all the information available, so that we may increase our understanding. Legal mechanisms should be considered for longer ownership of exclusive marketing rights of active ingredients, in exchange for complete public disclosure of the environmental fate and toxicology data submitted to regulatory agencies.

Common tansy [Tanacetum vulgare (L.) Bernh. ♯CHYVU], a native of Europe and Asia, is a perennial herbaceous composite growing erect to 1 m. It bears finely divided leaves and, in summer, umbels of small, button-shaped yellow flowers. It has had many traditional uses as medicine, preservative, and repellent from Medieval times to modern—uses which have been validated by contemporary research.