Experiments were conducted to determine the influence of spray carrier salts, UV light, and temperature on sethoxydim phytotoxicity to oat or yellow foxtail. Spray solution pH and ions present were both important to sethoxydim phytotoxicity to oat. Sodium and calcium salts were antagonistic to sethoxydim phytotoxicity only when the spray carrier pH exceeded 7. Ammonium salts and ammonium hydroxide were synergistic with sethoxydim, and the synergism was independent of spray solution pH. Ammonium sulfate, but not ammonium hydroxide, overcame sodium bicarbonate antagonism of sethoxydim. The antagonism of sethoxydim phytotoxicity by sodium bicarbonate was greatest in the presence of UV light and most pronounced when treated plants were exposed to mid-day sunlight. Sodium bicarbonate or low temperature may reduce the speed of sethoxydim absorption allowing for greater UV degradation of unabsorbed sethoxydim on the leaf surface.

In 1985, the Swedish government mandated a 50% reduction in agricultural pesticide use by 1990. The reference point was based on the average of total pesticide sales (kg ai) between 1981 and 1985. The goal was to halve the risks to users and to the environment. A two-pronged approach dealing with risk and with the actual reduction in agricultural pesticide use was developed. By 1991, 215 ‘unsafe’ or less effective pesticide products were withdrawn by producers or cancelled by the National Chemical Inspectorate, leaving only 322 registered. Additionally, the government was able to report a 47% reduction in agricultural pesticide use where 64, 54, and 2% reductions occurred in insecticides, herbicides, and fungicides, respectively. However, the treated area did not decrease. Pesticide reduction was achieved largely in cereal grain production by switching from high-dose to low-dose herbicides, reducing rates of herbicides, removal of inactive isomers from racemic mixtures, cancellation of TCA for quackgrass control, increased set-aside, and improved sprayer precision. During the same 5-yr period, Scotland achieved an equivalent reduction without government intervention, indicating that the reductions were largely due to changing herbicide technology. Determining the need for similar programs must take into account: 1. initial use rates (in 1987, average total pesticide use rates in the U.S. and in Sweden were 1.8 and 1.5 kg ai/ha, respectively, and following the mandate period, Swedish use has decreased to 0.8 kg ai/ha); 2. measurement criteria; and 3. the long-term effect of reducing herbicide rates on replenishing the soil weed seed bank reserves.

Current United Kingdom (UK) government policy on pesticides is aimed at minimizing rather than arbitrarily reducing usage. It is to be achieved through a rigorous Approvals process, the setting of statutory maximum residue limits, regular monitoring, legislation on the safe use of pesticides on farms, and a core-funded research program on topics such as improved forecasting of pest infestations, more effective application techniques, alternative control strategies, integrated pest management and sustainable farming systems. Over the longer term these measures are expected to bring about substantial real decreases in pesticide usage, without the need to impose arbitrary reduction targets, such as have been implemented by several other European countries. Reductions in the usage of particular chemicals will also occur as a result of the implementation of European Community (EC) environmental legislation on pesticide levels in ground and drinking water and pesticide discharges into the North Sea. With herbicides, the tonnage of active ingredient applied in the UK declined substantially during the 1980s, due mainly to the increased use of products which were more biologically active at lower dosage rates than those they replaced. The actual percentage of crops sprayed remained at 95 to 100. Further reductions are likely in the 1990s, enhanced by factors such as dose-cutting by farmers in response to economic rather than environmental pressures and an increase in set-aside. Weed scientists are currently studying the long-term effects on weed population dynamics of reduced herbicide inputs in cereals, set-aside management, and more environmentally friendly, lower input rotations, as part of a wider program of research designed to provide government with scientifically based information upon which to decide future policies.

Field experiments were conducted in 1991 and 1992 to evaluate corn tolerance to nicosulfuron following in-furrow or surface-band applications of seven soil-applied insecticides. The organophosphate insecticides evaluated included terbufos (15G and 20CR formulations), phorate, chlorpyrifos, fonofos, and DPX-43898, as well as the synthetic pyrethroid tefluthrin. Potential for a nicosulfuron/ insecticide interaction to injure corn was ranked as follows: terbufos 15G = phorate > terbufos 20CR > fonofos. Chlorpyrifos, DPX-43898, or tefluthrin followed by nicosulfuron caused no significant corn injury. Corn injury and yield reduction were greater in corn treated in-furrow compared with surface-band. Soil moisture at nicosulfuron application was more influential in causing corn injury and loss of yield than growth stage of corn at nicosulfuron application.

Pesticide registration in Canada is a Federal responsibility. Authority to recommend and use a pesticide often is Provincially controlled. A survey on “the status of pesticide reduction” within the various provinces of Canada revealed that only 3 of 10 had a policy to reduce pesticide use. In Ontario is an example of a successful non-mandatory program toward the reduced use of pesticides. A coordinated effort among government, industry, and growers has resulted in increased research, education, and extension for pesticide use. Licensing for sellers and users of pesticides has been effective in assisting the reduction of active ingredient pesticide sales.

Post-application seasonal (May-July) average concentrations of atrazine, cyanazine, and, to a lesser extent, alachlor sometimes exceed their Maximum Contaminant Levels (MCLs) (3 ug/L for atrazine and 2 ug/L for alachlor) or Maximum Contaminant Level Goal (MCLG) (1 ug/L for cyanazine) in surface waters of the Mississippi and Great Lakes Basins. These three chemicals are among the primary pre-emergent herbicides applied to corn. MCLs and MCLGs are compared to annual average concentrations for regulatory purposes. However, annual average concentrations are much less frequently reported than post-application seasonal averages. In most cases, both seasonal and annual average concentrations are substantially less than the MCLs or MCLG. However, actual and estimated annual mean concentrations occasionally exceed the MCLs or MCLG. Actual or estimated exceedences occur more frequently for atrazine and cyanazine than for alachlor, and may occur more frequently in lakes or reservoirs with long retention times than in streams and rivers. Additional year round data, and data for lakes and reservoirs, are needed to determine the extent to which such exceedences occur throughout the corn belt. The American Water Works Association (AWWA) believes that substantial numbers of Community Water Systems (CWSs) within the corn belt are currently, or will be, in violation of the revised Safe Drinking Water Act (SDWA) with respect to atrazine and cyanazine. They are concerned that such violations could result in numerous CWSs having to implement expensive tertiary treatment systems such as granular activated carbon to decrease herbicide concentrations. The United States Environmental Protection Agency, (US EPA) is continuing to review data on the pesticide concentrations in reservoirs and lakes that registrants have been submitting over the last 18 mo under the 6(a)(2) adverse impact provision of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). The US EPA is also currently using computer modeling and other methods to evaluate potential alternative and/or supplemental herbicides to reduce atrazine use. In June 1992, the US EPA approved revised labeling that is designed to reduce indirect atrazine loadings to surface waters. Additional mitigation methods have been proposed and are being considered.

The influence of incorporation vs no incorporation on the efficacy of granular triallate applied in mid-October at 1400 and 1700 g ai/ha to control wild oat was evaluated in spring wheat in west central Saskatchewan over a 7-yr period. All fall-applied triallate reduced wild oat panicles and fresh weight, and increased yield compared to untreated checks. With applications in standing wheat stubble there was no difference in wild oat control from incorporation versus no incorporation. All triallate treatments reduced wild oat panicles and fresh weight by over 95%, and resulted in wheat yield increases ranging from 29 to 67%. In tilled fallow, incorporated granules provided better wild oat control than when there was no incorporation. Wheat yield increases ranged from 50 to 85% for triallate treatments with yield for incorporated triallate approximately 15% greater than non-incorporated. The rate of triallate did not affect the level of wild oat control achieved with either incorporation method. In separate tolerance studies triallate incorporation method did not affect spring wheat emergence or subsequent development.

Our challenge is to develop a collective “vision” of environmentally sound agricultural systems for the future to enable us to produce food at twice our current level to meet the demands of a projected eight billion people in the year 2020. We must prove that our efforts are compatible with environmental concerns and our natural resources. Public concerns and regulatory pressures on pesticides are likely to increase throughout this decade and next. Can we produce a safe, abundant, and affordable food supply on limited land for more people, while maintaining an acceptable balance with nature? Sound, science-based public polices are essential. Industry and regulators must work together more closely, striving to understand each other better, as well as the needs of our customers and those of society. The research community, using guidance from our regulators, has provided environmentally compatible crop protection chemicals, like sufonylurea herbicides, products which are often applied at a factor of 50 to 500x lower than the conventional herbicides they replace. We will continue to discover new “ideal” pest control solutions, incorporating the best technology available. This “vision” of agricultural production for the future must be accepted and embraced not only by our industry and our regulators, but also by environmentalists, other interests and society as a whole. We must reach common ground to maintain a productive, economically viable, socially acceptable, and environmentally sound agricultural system to meet our future challenges.

Fall application of a PRE herbicide offers professional lawncare applicators additional flexibility in scheduling necessary weed control operations. A 3-yr field study was established on common Kentucky bluegrass in Urbana, IL to examine the effectiveness of fall- or spring-applied prodiamine and DCPA for spring large and smooth crabgrass control. Prodiamine was effective for crabgrass control in turf (≥ 91% control) when applied in spring at ≥ 0.4 kg/ha or when it was applied in the fall at ≥ 0.6 kg/ha (≥ 82% control). In most cases, fall-applied prodiamine at the 0.8 kg/ha rate (≥ 91% control) controlled crabgrass as well as spring-applied DCPA at the 11.8 kg/ha rate (≥ 94% control). Little reduction in turf quality (≥ 8.3) occurred when prodiamine was applied in the fall at 0.8 kg/ha or less. Only when prodiamine was applied at 2.2 kg/ha was there significant quality loss (7.3) with spring applications. In a second experiment to evaluate split fall and spring prodiamine applications for crabgrass control, all split applications had 100% crabgrass control which was not significantly different from single applications of ≥ 1.4 kg/ha.

The fate of field-applied herbicides, including losses in surface runoff with water and sediment, is highly dependent on herbicide properties. The two most important properties are soil adsorption and persistence. Adsorption affects the potential for a herbicide to be lost primarily with sediment, runoff water, or possibly leaching water. Solubility, often though not always inversely correlated with adsorption, is of secondary importance, although low solubility can limit transport with water. Persistence affects the time available to be lost in runoff. Studies have shown that for soil-applied herbicides; extraction into runoff water or movement with sediment takes place from a thin soil layer at the surface. In addition, for herbicides studied, there is little interaction between surface crop residue and applied herbicides, and washoff from the residue readily occurs with small amounts of rainfall. Runoff loss equals the volume of carrier (water or sediment) times the concentration in that carrier; therefore, practices that reduce either, or both, can reduce losses. Rate of application has been directly related to concentration and therefore loss. Reducing rate, such as by banding, soil incorporation, and avoidance of application to crop residue reduce losses. The choice of herbicide and herbicide formulation, in conjunction with application technology, as they affect properties, rate, and placement, play a large role in determining runoff loss. Runoff losses of herbicides that are strongly adsorbed and therefore transported mainly with sediment can be reduced by erosion control; runoff volume reduction can reduce losses with water of moderately to weakly adsorbed herbicides. Conservation tillage has potential to reduce both runoff and erosion. Timing of application relative to expected intense storms, both in the short and long term, can reduce the potential for runoff. If possible to determine thresholds, herbicide use could be avoided if weed infestation is below the economic effect level. Buffer or filter strips have the potential to reduce transport of herbicides lost from fields to surface water resources.

Turf managers use prodiamine to control annual grasses in mature turfs. Earlier, evaluations of prodiamine have indicated it has an elevated soil persistence and high activity on susceptible species. This persistence raises concern for prodiamine's effect on juvenile turf. An experiment was established to evaluate the effect of prodiamine on juvenile Kentucky bluegrass turf. Significant loss of quality occurred on turf less than one year old receiving a single application of prodiamine at ≥ 1.4 kg/ha. Split applications of prodiamine did not significantly decrease turf quality. Prodiamine at 0.8 and 2.2 kg ai/ha and DCPA at 23.5 kg ai/ha, applied in the fall the previous three years, significantly reduced the number of overseeded Kentucky bluegrass seedlings two years after planting. In a subsequent study, prodiamine at ≥ 0.8 kg/ha and DCPA at 23.5 kg/ha applied once the previous fall significantly reduced the number of overseeded Kentucky bluegrass dlings 56 d after planting. An analysis of prodiamine rate versus seedling density was found to be significantly correlated (r2 = 0.79).

Herbicides are an integral part of farmers' cultural practices worldwide. Growing concerns about agrochemical residues in the environment and in the food supply require a critical discussion about how to secure the environmental fitness of any weed management practice. Promising ways to minimize herbicide consumption include the introduction of new (low-rate) chemistries, the low-rate concept, innovative formulations, application timing, and a cropping systems approach. However, many questions with regard to crop/weed dynamics in different agricultural production systems require answers before final recommendations can be made, and the farmer has to occupy a central part of our considerations. Besides conducting more basic weed research to reduce herbicide rates, it will be equally important to integrate the efforts of all parties involved and to improve the communication with our customers, including the public, environmental interest groups, and politicians. To be widely accepted, weed management practices for the future have to be adapted such that the respective requirements of environment, society, and economics are fully met.

A major debate is going on in the United States regarding the proper methods for crop pest management. One issue in this debate is whether weed control should be based largely on nonchemical or chemical means. This isn't the only issue that should be of interest to weed scientists, but it is important, and it illustrates the need to extend weed science research to influence public policy.