A two-year herbicide residue study was conducted at a commercial nursery to determine the presence of herbicide residues in pond water and sediment following normal production cycles. The runoff water from irrigation and rainfall was contained on the nursery and reused for irrigation. The nursery site was approximately 60 ha with two interconnected ponds, one for containment of runoff water and one serving as a source of irrigation water. The most commonly used herbicides were oxyfluorfen plus pendimethalin (granular formulation-Ornamental Herbicide 2); approximately twice as much herbicide was applied during the second year of the study. Herbicide levels found in pond water and sediment were approximately two-fold greater during the second year corresponding to the increase in active ingredients applied. The highest concentration of oxyfluorfen found in water and sediment was 0.04 μg/ml and 4.0 μg/g, respectively. The highest concentration of pendimethalin found in water and sediment was 0.008 μg/ml and 14.3 μg/g, respectively. In irrigation water samples, the highest concentration of oxyfluorfen and pendimethalin detected was 0.005 μg/ml and 0.002 μg/ml, respectively. The herbicides did not accumulate in water or sediment over the two-year period. No landscape plant phytotoxicity problems are likely at the herbicide levels detected in irrigation water samples.

Manure applied to cropland may serve as a source of weed introduction and dispersal. In 36 manure samples from 20 farms, apparently-viable seeds from 13 grasses and 35 broadleaf plants were found. Common lambsquarters was on more than half the farms, yellow foxtail on 35%, common chickweed and dandelion on 30%, and wild mustard, redroot pigweed, and barnyardgrass on 25%. Four farms had manure with no seeds at all; the remainder averaged 75 100 per 1000 kg manure. Twelve milking-cow and heifer barns on six farms with large velvetleaf infestations also were sampled with an average of 133 000 seeds per 1000 kg manure. Only one barn contained velvetleaf seeds. When compared to soil seedbank numbers, manure is not an important seed source for New York farms. However, problems may arise with imported feeds heavily infested with weed seed or which contain even small numbers of noxious weeds.

Field experiments were conducted at Vegreville, Alberta in 1984, 1985, 1986, and 1988 to determine the effects of green foxtail and pale smartweed on yield of wheat, barley, and canola. There was considerable variation among years in the response of crop yield to both weeds and in the relationship between weed dry weight and weed density. Mostly relationships between crop yield and either weed density or dry weight were poor, suggesting that the weeds competed weakly with the crops. Thus density or dry weight may be poor predictors of crop yield losses due to green foxtail or pale smartweed. Where the crops emerged ahead of these weeds, and where soil moisture was not a limiting factor, crop yield losses were minimal and control with herbicides probably uneconomical. In some instances, growth and development of the weeds was suppressed by the crops to the extent that little or no weed dry matter was present at crop maturity. This was most evident with barley, and where the crops emerged ahead of the weeds.

In field experiments at three locations, wheat row spacing, seeding rate, and herbicide treatment affected Italian ryegrass control, wheat yield, dockage in the grain, and net returns. Diclofop at 560 or 840 g ai/ha controlled Italian ryegrass better than chlorsulfuron at 18 or 26 g ai/ha. Net returns were increased at all locations by diclofop POST at either rate and at two locations by chlorsulfuron PRE at either rate. Although increasing the wheat seeding rate reduced dockage at two of three locations, net returns were maximized by herbicide application alone without increased seeding rates or reduced row spacing.

Postemergence applications of nicosulfuron and primisulfuron were compared to preplant glyphosate and atrazine plus simazine for quackgrass control in reduced tillage and no-till corn. The level of quackgrass control was reduced by no-till practices. At 6 wk after planting, glyphosate and atrazine plus simazine were most effective in controlling quackgrass. Quackgrass biomass 12 wk after planting indicated that the performance of the herbicides were generally similar, although primisulfuron was less effective in no-till. One year after corn planting, levels of quackgrass control in the tilled plots were the same as or better than in the no-till treatments. Atrazine plus simazine was the most effective herbicide treatment over tillage systems, while primisulfuron was the least effective.

Phenmedipham was registered for use at 1.1 to 1.7 kg ai/ha in 1970 and desmedipham at 1.1 to 1.4 kg ai/ha in 1974 for postemergence control of broadleaf weeds in sugarbeet. Phenmedipham was sold from 1970 through 1981 and desmedipham plus phenmedipham (1:1), as a premixed product, has been sold since 1982. Development of multiple applications of reduced rates began in 1972 primarily to reduce sugarbeet injury. The technique was promoted to farmers after 1976. Ahalf-rate of phenmedipham and/or desmedipham applied twice at a 5- to 7-d interval controlled weeds better and caused less sugarbeet injury than a single full-rate application, and allowed application to smaller than four-leaf sugarbeet. Suggested sugarbeet size for the first application changed from 4-leaf in 1970 to cotyledon to two-leaf in 1992. Earlier application to more susceptible small weeds allowed a further rate reduction. The use of soil-applied herbicides prior to phenmedipham and/or desmedipham increased weed control and sugarbeet injury. Application to small weeds and sugarbeet by air or by ground sprayers at spray pressures over 1040 kPa controlled weeds better and injured sugarbeet more than when applied by ground sprayers at 280 kPa. Desmedipham and phenmedipham rates presently are adjusted for sugarbeet size, application method, soil-applied herbicide, and environment. The suggested initial application rate of phenmedipham and/or desmedipham in 1992 was 0.13 to 0.28 kg/ha as compared with 1.1 to 1.7 kg/ha in 1970. A typical rate of desmedipham or desmedipham plus phenmedipham applied in 1992, including multiple application, was approximately 0.7 kg/ha less than typical rates from 1970 through 1977.

During the early years of herbicide use, the total amount of ai applied per ha increased in attempts to obtain season-long weed control, peaking in the decade of the mid-1970's to mid-1980's. Since then, the chemical load applied for broadleaf weed control has shown a consistent, if not dramatic, decline. A much more significant reduction has occurred in grass weed control. Main reasons for the reduction are a move from PPI and PRE treatments to POST, the development of repeat low-dose herbicide techniques, and the introduction of more active postemergence grass herbicides. In general, this change has been achieved with a concomitant improvement in crop safety. These developments occurred as a coincident benefit in pursuing the target objective of giving growers more convenient and flexible weed control and not as a specific attempt to reduce chemical use. This paper discusses the evolution of weed control programs in the U.K., France, Germany, and the U.S.A. All show a similar trend, though the pace of change has been slower in the U.S.A.

There is distinct regional variation in forestry uses of herbicides. Different land ownership patterns affect policies and practices, and crop tree species characteristics differ within and among regions. Recent decreases in land areas treated have been attributed to budget reductions, changes in operating conditions, and pressures from the general public. Factors affecting future reductions in amounts of herbicides used will include new chemistry, improved delivery technologies, incorporating vegetation management into all aspects of young stand silviculture, and employment of alternative methods.

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.

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.

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.

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.

The first weed scientists were under great pressure to solve weed problems and when the magic of chemical technology appeared they seized it to replace human and animal energy for weeding. Today, weed scientists are striving for a reasonable accommodation between a productive and protected environment. Many weed scientists now believe that management, not control, should dominate weed science. Full integration of weed science into future agricultural systems requires that its practitioners make the quality and quantity of food produced equivalent goals.

The purpose of my presentation is to demonstrate the impact that weeds have on man and the U.S. economy. My approach will be to introduce the concept of weed impacts. What do I mean when I reference weeds and the effects that they have on man and his activities? Second, what are the sectors of the U.S. economy that are impacted by weeds? Third, I will illustrate the types of impacts that weeds have on various sectors of the economy and I will categorize these impacts so that they become meaningful. Last, I will discuss the economics of weed management, covering indexes of weed management inputs over time and discuss the relative value of various weed management tactics.

For this presentation we would like to discuss some history of weeds and their control, the evolution of weed science, the development of herbicides and the changing dynamics of weed science research. As mentioned by previous speakers, weeds cause great loss to almost every crop production enterprise in the United States and around the world. Man has sought to control weeds by various methods including cultural practices, cultivation, hoeing, and with herbicides. Pioneer weed scientists were individuals trained in the areas of physiology, botany, and agronomy. They applied their knowledge and training to the understanding of growth, development, and control of weeds in the late 1800's and early 1900's.

Concerns in the public and agricultural sectors about the impacts of agricultural practices have led many weed scientists to refocus research efforts toward development of alternative strategies of weed management. To develop methods of weed management that will supplement or replace herbicides, the impacts of agricultural practices on weeds must be better understood. With a foundation of knowledge in basic weed biology, alternatives to herbicides can be made available in the future.