Living mulches are cover crops grown simultaneously with and in close proximity to cash crops. Advantages of living mulches over dead cover crops may include increased weed suppression, reduced erosion and leaching, better soil health, and greater resource-use efficiency. Advantages of living mulches over synthetic mulches may include enhanced agroecosystem biodiversity and suitability for a wider range of cropping systems. A major disadvantage of this practice is the potential for competition between living mulches and cash crops. The intensity and outcome of mulch-crop competition depend on agroecosystem management as well as climate and other factors. In this review, we consider the management of living mulches for weed control in field and vegetable cropping systems of temperate environments. More than 50 yr of research have demonstrated that mechanical or chemical suppression of a living mulch can limit mulch-crop competition without killing the mulch and thereby losing its benefits. Such tactics can also contribute to weed suppression. Mechanical and chemical regulation should be combined with cultural practices that give the main crop a competitive advantage over the living mulch, which, in turn, outcompetes the weeds. Promising approaches include crop and mulch cultivar selection; changes to planting time, density, and planting pattern; and changes to fertilization or irrigation regimes. A systems approach to living mulch management, including an increased emphasis on the interactions between management methods, may increase the benefits and lower the risks associated with this practice.

Striking a balance between the weed control capacity of living mulches and their competition with the main crop is complex. At rates that avoid severe injury to living mulch, herbicides may reduce their vigor while simultaneously contributing to weed control. In a 2-yr field study carried out in Freeville, NY, we evaluated the effects of various combinations consisting of two herbicides, applied sequentially at reduced rates, on the growth of a sunn hemp living mulch and weeds (including common lambsquarters, common purslane, hairy galinsoga, and Powell amaranth). When a herbicide with primarily POST activity (Type 1; e.g., rimsulfuron, 0.005 to 0.007 kg ai ha−1) was applied first, performance of sunn hemp (1700 to 3900 kg ha−1 dry biomass; 10% to 88% groundcover) was poor and weed growth (25% to 62% groundcover) was high, likely because sunn hemp was severely injured at a young growth stage and was outcompeted by weeds. A follow-up application (approximately 2 wk later) of a herbicide with primarily PRE and residual activities (Type 2; e.g., metribuzin, 0.05 to 0.15 kg ai ha−1), with a surfactant to enhance its POST activity, had little effect on established weeds. However, because sunn hemp was already 20 cm tall at weed emergence, applying a Type 2 herbicide first did not cause severe injury to sunn hemp and reduced weed pressure, thereby also enhancing sunn hemp performance (3,800 to 6,100 kg ha−1 dry biomass; 85% to 94% groundcover). Moreover, the follow-up application of a Type 1 herbicide affected the smaller weeds more (4% to 21% groundcover) than the better-established sunn hemp. Our results demonstrate that an appropriate sequence of herbicides at reduced rates may be important to control weeds while maintaining a healthy living mulch stand.

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 studies determined the influence of developmental stage on mow-killing of winter wheat and rye. Both crops were clipped at either three or four different growth stages in 1992 and 1993. When mowed at first node, wheat biomass was 4350 and 1970 kg/ha in 1992 and 1993, respectively. At this stage, primary tiller apices were below 10 cm and regrowth was vigorous. Mowing prior to 75% heading consistently yielded more than 1000 kg/ha regrowth 8 wk later. Wheat cut after flowering produced 15 460 and 9160 kg/ha dry matter in 1992 and 1993, respectively, but less than 30 kg/ha total regrowth. At first and second node, rye produced 4440 and 1800 kg/ha biomass in 1992 and 1993. When mowed belore boot, more than 50% of the total rye biomass was due to regrowth. Rye mowed at boot yielded 6940 and 3740 kg/ha in 1992 and 1993 respectively, and regrowth measured 780 and 910 kg/ha 8 wk later. Mowing after flowering resulted in no measurable regrowth. Soil temperature and PAR were affected by mow-kill date and biomass. Biomass at first mowings (first and second node) in both wheat and rye reduced seasonal soil temperatures 3.5 C compared to bare soil temperatures; while biomass at kernal-filling lowered temperatures 6.0 C. Measured 8 wk after mowing, first node mowings absorbed between 55% and 70% PAR, while plants mowed at kernal-filling absorbed less than 5%.

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.

Time of hilling (4, 5, or 6 weeks after planting; WAP) and 0.5x, 1x, and split (0.5x + 0.5x) rates of metolachlor + metribuzin were evaluated in conventional tillage (CT) and rye-stubble, reduced tillage (RT) potato plots. Weed populations 4 to 10 WAP were generally higher in CT than in RT. Weed control was excellent in both tillage systems when 1x rates of metolachlor + metribuzin were applied delayed preemergence, or in a split application where 0.5x was applied delayed PRE and hilled 6 WAP, and followed with a second application of 0.5x metolachlor + metribuzin 7 days after hilling (DAH). Weed control with 0.5x rates of metolachlor + metribuzin applied 7 DAH, when hilled 4 and 5 WAP, was equivalent to the lx and split-rate treatments. Weed control was reduced only when hilling was delayed to 6 WAP and 0.5x of metolachlor + metribuzin applied 7 DAH. Total yields were not influenced by tillage, hilling, or herbicide treatment, however, larger numbers of green and small-sized tubers reduced marketable yields in RT.

Following suggested guidelines developed by the Environmental Protection Agency (EPA), comparative snap bean herbicide performance field trials were conducted from 1993 to 1995 in New York. Data were obtained on crop injury, weed control, and weed biomass, and crop yield, quality, and losses during harvest. Trifluralin, EPTC, and pendimethalin applied preplant incorporated (PPI) and applications of metolachlor applied preemergence (PRE) provided less than adequate control of redroot pigweed, common lambsquarters, and hairy galinsoga. Cultivation improved weed control with PPI and PRE applications. Metolachlor + fomesafen PRE provided good control of hairy galinsoga, adequate redroot pigweed control, and marginal control of common lambsquarters. Fomesafen applied postemergence (POST), combinations of metolachlor applied PRE with fomesafen or bentazon applied POST, and fomesafen + bentazon applied POST adequately controlled the three weed species without cultivation. Herbicide treatments had little measurable impact on snap bean quality or losses during harvest. Information from product comparison trials may be useful in developing recommendations for growers but may prove less than adequate in providing data necessary for a thorough evaluation of the relative benefits of individual herbicides as intended by EPA guidelines. Difficulties were encountered in following the guidelines, and costs of conducting the product comparison trials for a single crop in one growing region exceeded $90,000 over 3 yr.

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.

Five cultivation implements (two flex-tine cultivators, brush hoe, and rolling and shovel cultivators) were evaluated for weed control and effect on broccoli, snap bean, and sweet corn yield. Each implement was used alone or in combination with flex-tine cultivators. Standard broadcast herbicide treatments were: broccoli, metolachlor at 2.3 kg ai/ha posttransplant; snap bean, metolachlor preemergence (PRE) at 2.3 kg ai/ha followed by fomesafen postemergence (POST) at 0.4 kg ai/ha; sweet corn, atrazine at 1.1 kg ai/ha plus metolachlor at 2.3 kg ai/ha PRE. In the snap bean trials, an additional treatment consisted of metolachlor at 2.3 kg ai/ha PRE applied in a 25-cm band over the crop row followed by fomesafen POST at 0.4 kg ai/ha directed at the crop row, with a subsequent shovel cultivation. In the sweet corn trials, all cultivation treatments received an application of atrazine at 1.1 kg ai/ha plus metolachlor at 2.3 kg ai/ha PRE in a 25-cm band over the crop row. In broccoli, weed control and yields with all cultivation treatments were comparable to those with broadcast herbicide. In snap bean, flex-tine cultivators failed to control weeds and prevent yield reductions compared to the broadcast herbicide treatment. When either the brush hoe or the shovel cultivator was preceded by flex-tine cultivation, weed control and snap bean yield were comparable to those with broadcast herbicides. Banded herbicides followed by shovel cultivation also controlled weeds and prevented yield reductions. In sweet corn, banded herbicides controlled in-row weeds, and despite variable between-row weed control, all cultivation treatments yielded as well as the broadcast herbicide treatment. Relative performance of the cultivators was influenced by soil type and rainfall as well as crop canopy characteristics.

Experiments compared the effect on weed control and potato yield of banded applications of metolachlor plus linuron with or without flex-tine, rolling, and shovel cultivation prior to hilling. Cultivation without banded herbicide resulted in greater prehilling in- and between-row weed densities and reduced late-season weed control as compared to broadcast herbicides or cultivation with banded herbicides. Although the flex-tine and rolling cultivators were expected to provide improved in-row weed control, there were few differences between these and the other cultivation implements. Despite reduced weed control with cultivation alone, potato yields were not reduced.