Field experiments in 1988, 1989, and 1990 evaluated the response of four pepper cultivars to PPI applications of metolachlor at Las Cruces and Artesia, New Mexico. Metolachlor at ≥ 2.2 kg ai ha–1 in 1988 and 4.5 kg ha–1 in 1990 reduced overall green pepper yields only in a Harkey very fine sandy loam soil at Artesia. Metolachlor at ≥ 2.2 kg ha–1 reduced the yield of the jalapeno cultivar ‘TAM’ and at 4.5 kg ha–1 reduced the yield of New Mexico cultivar ‘NM 6-4’ and a proprietary New Mexico cultivar in 1988. Metolachlor did not reduce the yield of any cultivar in 1989 or 1990. Metolachlor bioactivity on NM 6-4 pepper was similar in the three soils regardless of irrigation water source. Emergence of peppers was ranked Belen clay loam = Rakor loam > Harkey very fine sandy loam when the greenhouse temperature approximated field conditions. Under conditions where germination and emergence of peppers was reduced by an interaction between soil factors and temperature, further stand reduction due to metolachlor treatment caused yield reductions.

Field studies were conducted at three locations in Louisiana over two years to evaluate mid-season, foliar-applied acifluorfen, fomesafen, and lactofen for hemp sesbania control in soybean. Acifluorfen and fomesafen were applied POST at 30, 40, 50, 60, 70, 140, and 280 g ai ha–1 and lactofen was applied at 60, 80, 110, and 220 g ai ha–1. The data fit a quadratic model and log transformations were made to determine differences between treatments. Hemp sesbania control was highly correlated with herbicide rate for each herbicide. Averaged over rates of application, acifluorfen and fomesafen provided equivalent control of hemp sesbania, which was greater than that achieved with lactofen. The minimum effective rate of acifluorfen or fomesafen for 80 and 100% control of 50- to 60-cm hemp sesbania was 50 and 140 g ha–1, respectively. The minimum effective lactofen rate to provide at least 80% control was 220 g har–1.

Glyphosate and SC-0224, at rates that control dodder (75 to 150 g ae ba–1), injured flowers, caused flowers to abscise, and sometimes reduced seed yields when applied to alfalfa when buds or blooms were present. Glyphosate at 75 or 150 g ha–1 did not injure flowers, impair seed set, or reduce yield or quality of seed when applied to alfalfa foliage before the bud stage.

Twenty determinate soybean cultivars were grown in hydroponic solutions to determine differential tolerance to chlorimuron and imazaquin at pH 6, 7, or 8. ‘Epps' exhibited tolerance to chlorimuron at each pH, and to imazaquin except at pH 8. ‘9641 Pioneer’ was highly sensitive to both herbicides at each pH, and ‘Asgrow 5979’ was sensitive to chlorimuron, and to imazaquin except at pH 7. ‘Hutcheson’ was sensitive to chlorimuron at each pH, and imazaquin at pH 6. ‘Asgrow 6785’ was sensitive to chlorimuron at pH 6 and 8, with shoot weight reductions of 31 and 28%, respectively, and ‘Coker 686’ was similarly sensitive at pH 6 and 7. ‘Hartz 6200’ was tolerant to imazaquin at pH 6 and 7, ‘Hartz 6686’ was tolerant at pH 6 and 8, and Coker 686 was tolerant at pH 7 and 8. Coker 686 and 'Sharkey’ were tolerant to chlorimuron at some pH levels, though highly sensitive at other pH levels. ‘Asgrow 5403’ and Coker 686 also had varying tolerance and sensitivity to imazaquin across pH levels. Shoot length and shoot weight were the best indicators of differential cultivar sensitivity when compared with previous field studies.

Field experiments were conducted in 1989 and 1990 to evaluate differential soybean cultivar tolerance to chlorimuron and imazaquin applied PPI, as influenced by soil moisture. Natural rainfall was supplemented with irrigation to achieve three moisture regimes: low (nonirrigated), optimum (5 cm wk–1), and excessive (15 cm wk–1). Imazaquin at 140 g ai ha–1 did not adversely affect height or yield of cultivars under any of the moisture regimes. Excessive moisture, regardless of herbicide treatment, reduced height and yield with many of the cultivars. Chlorimuron at 80 g ai ha–1 caused additional plant height reductions of 8 cm or more with ‘Asgrow 5403% ‘Asgrow 5979’, ‘Coker 686’, ‘Asgrow 6785’, ‘Hartz 6686’, and 'Sharkey’ in the excessive moisture regime, and yield was reduced 450 kg ha–1 or more with ‘Hutcheson’, ‘Terra-Vig 515’, Coker 686, Asgrow 6785, and Hartz 6686. Chlorimuron in the optimum moisture regime reduced the height of Coker 686 and ‘Deltapine 566’ 10 and 11 cm, respectively; however, no yield reductions were noted.

Experiments were conducted from 1988 through 1991 to evaluate the effectiveness of imazethapyr alone and in combination with metolachlor for control of yellow and purple nutsedge. Imazethapyr alone at 0.07 kg ha–1 controlled yellow nutsedge irregularly while the addition of metolachlor greatly improved control. Metolachlor preplant incorporated (PPI) followed by imazethapyr at ground-crack (GC) or postemergence (POST) controlled 72 to 96% of yellow nutsedge, whereas a tank-mix of metolachlor plus imazethapyr PPI controlled 85 to 96%. The addition of metolachlor to imazethapyr did not result in any improvement in control of purple nutsedge. Metolachlor plus imazethapyr PPI controlled ≥ 85% of purple nutsedge PPI, whereas imazethapyr POST controlled ≥ 94%.

The efficacy of nine granular formulations of a bioherbicide containing the fungus Sclerotinia sclerotiorum (Lib.) de Bary was determined by assessing vegetative growth from tap roots of treated plants after incubation in a controlled environment. Plants treated with formulations 0788-03 or 0788-04 did not produce new petioles and leaves from tap roots after 96 h at 23 C and 100% relative humidity.

Studies were conducted in 1989 and 1990 to determine the phytotoxicity of chlorimuron and tank mixtures on ‘Florunner’ peanut. Chlorimuron plus a petroleum oil adjuvant or 2,4-DB was more phytotoxic (P = 0.05) than chlorimuron plus a nonionic surfactant, based on stunting and chlorosis. Chlorimuron mixed with chlorothalonil, chlorothalonil plus sulfur, or esfenvalerate were no more phytotoxic than the standard. Adding sulfur or nonionic surfactant to chlorimuron plus chlorothalonil did not affect phytoxicity. Sequential applications of chlorimuron and 2,4-DB did not completely negate the phytotoxicity of the tank mixture. Despite differences in phytotoxicity, yields were not reduced.

Field research was conducted in 1988 and 1989 to compare effects of clethodim, fenoxaprop, haloxyfop, and sethoxydim each applied singly and sequentially at full (1X) and reduced (0.5X) rates on barnyardgrass, bearded sprangletop, and rice. A tank-mixture of propanil plus thiobencarb (2.2 + 2.2 kg ha–1) applied sequentially was included as a standard treatment. Control of barnyardgrass and bearded sprangletop was equal to that of the standard treatment both years with 1X rates of clethodim and fenoxaprop, and with 0.5X rates of clethodim, fenoxaprop, and sethoxydim each applied after propanil; rice so treated produced high grain yields. In 1988, severe rice injury occurred after the second application of clethodim at the 0.5X rate, but rice recovered. Grass control costs were reduced 57% with a single application of fenoxaprop at the 1X rate compared with the standard treatment, but net returns were not different.

The effects of droplet size and numerical deposit density on herbicide efficacy differed among investigations that relied on commercial nozzles to produce droplets strictly within small, medium, or large sizes. A droplet generator capable of producing uniform and homogeneous droplets was therefore used in a greenhouse experiment. Four droplet size classes (150, 350, 450, and 650 μm) using glyphosate, hexazinone, and triclopyr on red alder, aspen, and white birch were studied. Herbicides applied in small (150 to 450-μm) droplets were more phytotoxic than large (660-μm) ones because of their greater numerical coverage and translocation. Leaf age, weed species, herbicide type, and mixture of droplet sizes were not critical in modifying the effects of droplet behavior; however, the concentrations of herbicide used had a positive effect. When the herbicides were applied at high concentrations, the influence of droplet size was nullified. These findings may help reduce the cost of application and the chemical burden in a forest environment.

Two relatively new methods for analyzing herbicide efficacy data are described. Weighted multiple regression using the logit transformation for plant mortality data is illustrated and compared with the more accurate maximum likelihood logistic regression procedure. A partial data set evaluating the effects of increasing application rates of picloram (0, 1.1, 2.2 and 4.5 kg ae ha–1) for control of tall larkspur is used to illustrate the methods. Suggestions are made for using logistic regression to monitor herbicide efficacy over several years.

The effect of two dates of initial manual weeding, i.e., before flowering and after flowering, and of no weeding on yield of a local groundnut variety was studied during 1988 and 1989 at Minkoameyos, Yaounde, Cameroon, in comparison with chemical weed control method or control. The use of herbicides ametryn plus promotryn for weed control gave the best mean yield, followed by handweeding after flowering, and handweeding before flowering, in that order. The no weeding treatment had the lowest yield throughout the trial period.

In a three county area, the density of musk thistle was higher than plumeless thistle in pastures in the easternmost county, equivalent in the central county, and lower in the westernmost county. Bull thistle was detected frequently, but density was always low. Detection of Canada thistle decreased from east to west.

Sulfonylurea herbicide-resistant prickly lettuce was discovered in Idaho in 1987. The objectives of these surveys were to determine the change with time in the proportion of sulfonylurea resistant and susceptible prickly lettuce biotypes on the farm where it originally occurred, and to determine the spread of sulfonylurea resistant prickly lettuce beyond its point of origin. On average, the proportion of resistant plants had decreased from 1988 to 1990, a period when sulfonylurea herbicide use was discontinued on the farm. Resistant prickly lettuce plants were found at seven sites away from the original infested farm. Several sites were near the farm along roadsides that had been sprayed with sulfometuron. This study shows that the proportion of resistant prickly lettuce decreased where previously found, but its range increased.

An experimental directed sprayer has been improved for use in conservation-tillage and no-tillage field conditions and variable row widths. The directed sprayer consists of a rear-mounted toolbar with individually flotational spraying units on lightweight runners which move over field surfaces without the collection of loose residues. Improvements allow convenient adjustments which combined lateral, vertical, angular, and fore-and-aft repositionings to correctly aim the hydraulic nozzles for desired pesticide targeting. Such new designs are needed to deliver pesticides to targets at minimum application rates and with minimum environmental impacts.

Two introduced windgrass species have become crop weeds in North America. Common windgrass is a major weed of winter cereals in Europe and was first documented in North America in the early 1800s. It is a weed of roadsides and waste areas in the northeastern United States and in winter grain fields of southern Ontario and Michigan. Interrupted windgrass was first reported in North America approximately 90 yr ago; it is adapted to more arid sites than common windgrass and is distributed predominantly in the northwestern U.S.A. During the past 10 to 15 yr, interrupted windgrass has adversely affected winter grain and grass seed producers in the Pacific Northwest due to additional control costs.

The environment for agricultural research and development, technology transfer, and production is marked by conflict among persons with diverse ideas and goals for agriculture. The objective of this analysis was to identify and compare models for researching and problem solving that can provide a conceptual framework for understanding and improving complex situations marked by conflict. The research activities of scientists involved in development of genetically-engineered-herbicide resistance were modeled as reductionist science, technology development, and optimizing systems. An analysis of these models of goal-seeking research indicated that values and assumptions implicit in goals such as greater productivity were not evaluated or questioned. Views of experts influenced development and application of technologies and systems more than concerns of producers and society. A soft systems methodology and research system is proposed to involve more diverse ideas or views of the world, to shift the role of the researcher from expert to facilitator, and to move toward consensus concerning research and technology development in agriculture.

The strategy to optimize weed management systems with a minimum use of herbicides includes both the adaptation of crop management practices and well designed decision making systems, based on postemergence observations of weed infestations. Both strategies require thorough quantitative insight into the crop weed ecosystem, which can be provided by systems analysis, using process based models. These models also can be applied to similar systems like intercropping. For practical application, however, a simple measure of weed infestation and a simple model which relates weed infestation to yield loss are required. Recent progress in model development is discussed. An alternative empirical model that predicts yield loss from the relative leaf area of the weeds shortly after crop emergence, seems to be a useful approach for prediction of yield loss shortly after crop emergence. The use of systems approaches at different levels of detail for bridging the gap between research and practical application is discussed.

Organizer's comments: Systems inquiry represents an array of research-based problem-solving approaches. European experience with the pesticide debate suggests several simple messages contained in this paper. As weed scientists, we have everything to gain by considering a global sphere of views, practices, logic, experience, and message. Read this paper for the essence, the message, the systems thinking, the research framework, and the interface between society and weed science. Read it because science and society must communicate.