In 1982 and 1983, effects of soybean row spacing and irrigation on weed resurgence following postemergence herbicide applications were evaluated. Also, ‘Forrest’ and ‘Ransom’ cultivar effects and early and late planting date influences on weed resurgence were evaluated in 1982 and 1983, respectively. In both years, as row spacing increased, weed resurgence increased. Photosynthetically active radiation measurements indicated the amount of weed resurgence coincided closely with the differing amounts of light penetrating to the soil surface. Irrigation, planting date, and cultivars showed no significant effect on weed resurgence. In 1982, a significant cultivar by row spacing interaction was obtained. In 1983, the late planting date showed a trend for less weed resurgence under irrigated conditions, although the difference was not significant. Soybean canopy measurements indicated development was greater under irrigation.

Thirty soybean cultivars were grown in a hydroponic culture to observe differential tolerance to AC 263,222. Root length was reduced with 1.1 mM AC 263,222 in 18 of the 30 cultivars. ‘Bedford’, ‘Asgrow 5403’, and ‘Asgrow 6297’ were cultivars with a root length reduction of 30% or more, whereas roots of ‘DPL 506’, ‘RA 606’, and ‘Coker 6727’ were reduced less than 7%. Root weight was reduced in only 10 of the 30 cultivars. Asgrow 6297, ‘Bragg’, and ‘Narow’ root weights were reduced more than 20%. Shoot weight was reduced in 23 cultivars, and ‘Coker 6955’, ‘Braxton’, ‘Coker 485’, ‘Epps', and Coker 6727 shoots were reduced more than 25%. The most tolerant cultivars were ‘Centennial’, RA 606, ‘Tracy M’, ‘Johnston’, and ‘Hartz 7126’. The most sensitive cultivars to AC 263,222 with all response variables measured were Bedford, Asgrow 6297, Asgrow 5403, Coker 6955, Narow, Bragg, and Braxton. These cultivars all have ‘Jackson’ as a common parent. This suggests a genetic basis for AC 263,222 sensitivity in soybean.

Creeping wartcress was first identified in the Imperial Valley of southeastern California in 1982. From two limited invasions of approximately 2 ha each, by 1987 this weed had infested 1500 ha. Creeping wartcress can behave as an annual or biennial weed and is a member of the mustard family (Brassicaceae). Creeping wartcress seed germinates from September through March and flowers first appear in racemes in late February, continuing through May.

Research was conducted to determine the influence of salts on 2,4-D toxicity to kochia. Calcium, magnesium, sodium, potassium, and iron salts except for sulfate and phosphate salts of calcium and sodium were antagonistic to 2,4-D diethanolamine. None of the ammonium salts antagonized 2,4-D control of kochia. Effects of individual ions generally antagonistic to 2,4-D were additive when in mixture. 2,4-D generally controlled kochia better when mixed with various acids than with their ammonium salts in distilled, sodium bicarbonate, or ferric sulfate water carriers, relating to the lower pH with the acids. However, low pH was not essential in overcoming salt antagonism of 2,4-D for kochia control, nor was 2,4-D always effective with low pH. Sulfate and monobasic phosphate anions were most effective in overcoming sodium bicarbonate and calcium chloride antagonism of 2,4-D. The concentration of diammonium sulfate needed to overcome sodium bicarbonate antagonism of 2,4-D increased with sodium bicarbonate concentration. Diammonium sulfate at 2% (w/v) overcame 1200 mg L–1 sodium as sodium bicarbonate. Nonionic surfactants and oil adjuvants also overcame antagonism of 2,4-D caused by water from several sources.

Field experiments were established in 1989 and 1990 to determine the effects of application rate and timing on sicklepod control and soybean tolerance to POST applications of AC 263,222 and chlorimuron. When applied to 3-, 6-, or 10-leaf sicklepod, 35 g ai ha-1 or more AC 263,222 controlled more than 85% of sicklepod early in the season, and season-long when applied to 3- or 6-leaf sicklepod. At all timings, 70 g ha-1 or more AC 263,222 resulted in better control than a PRE application of 420 g ai ha-1 metribuzin followed by 9 g ai ha-1 chlorimuron applied POST. At 35 g ha-1 or more AC 263,222, application timing did not affect sicklepod control. However, control was reduced with 18 g ha-1 when applications were delayed from 3- or 6-leaf to 10-leaf sicklepod. At the 10-leaf sicklepod growth stage, a PRE application of imazaquin increased both sicklepod control and soybean yield with 35 g ha-1 AC 263,222 as compared with AC 263,222 applied alone. Soybean injury and height reductions with AC 263,222 at 35 g ha-1 and above were greater than with chlorimuron; however, increased soybean injury or height reduction was not reflected in pod numbers or yield.

Bentgrass was used to bioassay oxyfluorfen in leaching experiments done in columns of soilless potting media and soils, with herbicide incorporated into the upper 2 to 4 cm. Depth of herbicide leaching increased in order in the following soils: peat and sand (1:1) mix, Stockton clay soil, Yolo fine sandy loam soil, and redwood bark and sand (3:1) mix. Depth of leaching was not related to soil organic matter content. Equilibration experiments showed that peat adsorbed 4 to 5 times more oxyfluorfen than redwood bark. Less leaching was observed in potting mixtures containing peat than bark. Raising the oxyfluorfen dose from 20 to 200 ppmw increased the depth of leaching and concentration of herbicide in the leachate, while a 10-fold increase in water volume had only a limited effect. Twenty ppmw of oxyfluorfen incorporated in the top of a peat-containing potting medium has a low risk of leaching out of the container.

A 4-yr field study was conducted near Grassrange, MT to determine the effects of single and repetitive picloram treatments for leafy spurge control in a native pasture. Single applications of picloram at 0.28, 0.56, 0.84, and 1.12 kg ae ha–1 averaged 0, 5, 22, and 61% leafy spurge shoot control 3 yr after treatment. Only the single applications of picloram at 1.68 and 2.24 kg ha–1 maintained leafy spurge control above 80%. A retreatment with 0.56 kg ha–1 picloram was required to maintain effective control for 3 yr when less than 1.68 kg ha–1 was applied. Leafy spurge canopy cover in the 1.68 and 2.24 kg ha–1 treatments averaged 14 and 6% 3 yr after treatment; however, all other single applications required retreatment.

The adoption of herbicide use within Illinois has passed through four stages characterized by methods of application. These stages include an initial stage of POST applications, the PRE stage, the PPI stage, and the most recent stage marked by diversification of application methods. Data from 19 pesticide use surveys conducted in Illinois since 1957 were used to determine trends in pesticide use. Herbicide use has increased from 33% of the corn and 1% of the soybean hectarage treated in 1957 to applications on approximately 97% of all the corn and soybeans in 1990. Total herbicide use in Illinois peaked at 3.0 × 107 kg ai annually in 1982 and declined to 2.1 × 107 kg in 1990. Total herbicide use in Illinois between 1950 and 1990 is estimated at 5.0 × 108 kg ai.

Paraquat was applied at 0.28 and 0.56 kg ai ha-1 to winter wheat at five growth stages at 0800, 1300, and 1600 hr to determine whether growth stage or time of application influenced winter wheat response to paraquat. Paraquat bioactivity was affected by growth stage. Biomass reduction by paraquat was 84% when winter wheat was in the 1 to 3 leaf stage, but only 68% when application was delayed until tillering. Paraquat bioactivity continued to decrease at later growth stages. The time of day when paraquat was applied did not affect its bioactivity on winter wheat.

Field experiments were conducted to compare the timing of non-selective herbicide application on common lambsquarters under reduced tillage culture after wheat harvest. Common lambsquarters was controlled more effectively with herbicides applied to plants that were allowed to recover from removal of topgrowth during wheat harvest. When herbicides were applied immediately after wheat harvest, only glufosinate (HOE-39866) at the low and medium rates provided greater than 70% control.

Experiments were conducted over 2 yr and at two locations in Central Georgia to determine the influence of paraquat applied for weed control in the spring and following first harvest on alfalfa yield and crown carbohydrate content. Paraquat at 0.28 and 0.56 kg ai ha-1 controlled most annual cool-season weeds at 20 d after March treatment. These rates controlled annual warm-season weeds when applied as early as 7 d after first harvest. Treatments applied during March and as late as 7 d after first harvest did not influence alfalfa production or crown carbohydrate content. However, paraquat applied 14 d after first harvest reduced alfalfa yield 40% and significantly decreased crown carbohydrate content at second harvest but the alfalfa had fully recovered by the third harvest. This indicates that alfalfa is resilient to chemical defoliation by paraquat applied for weed control.

Process-level simulation models can be a unique and effective medium for teaching concepts of crop biology and management which can usually only be studied in the field. WEEDING was developed from several research models to demonstrate concepts of weed ecology, herbicide efficacy and selectivity, and economic thresholds for weed control decisions. Users of WEEDING interactively grow a soybean crop, making management decisions throughout the seaason. The program includes real weather data and a realistic assortment of soybean varieties, soil types, weed species, and weed control options. Production costs and profit are calculated at the end of a simulated season. The structure of a process-level model driven by real weather data simulates the risk involved in management decisions.

An invert emulsion with low viscosity and excellent water-holding properties was developed for delivery of fungal weed pathogens (mycoherbicides). Alternaria cassiae, a pathogen of sicklepod, proliferated after incorporation of spores in the emulsion. The oil phase (CDQ-1) contained paraffin wax, a paraffinic spray oil, and an unsaturated monoglyceride emulsifier (Myverol 18–99). The oil phase was mixed 1:1 (by weight) with water to form the invert, which was sprayed onto glass plates for testing of water retention properties. Water contents ranged from 22% (with A. cassiae present) to 41% (without fungus) for 0.6 to 0.7-mm2 spray deposits after 24-h storage at 21 C and 65% relative humidity. An invert emulsion containing lactofen was prepared using the CDQ-1 formulation.

Several precision postemergence-directed sprayers with different nozzle designs and arrangements were evaluated for potential use in sweet corn for wild-proso millet (PANMI) control in field trials from 1987 to 1989. Ametryn at 2270 g ha-1 plus oil-emulsifier mixture (OEM) at 1.3% v/v and sethoxydim alone or plus OEM applied postemergence-directed selectively controlled PANMI in sweet corn. Sethoxydim at 220 g ha-1 plus OEM controlled PANMI best when averaged over the 3-yr period. Ametryn plus OEM did not injure corn and sethoxydim at 110 g ha-1 plus OEM caused little or no corn injury and no yield reductions when applied with any of the sprayers. Generally, only sethoxydim at 220 g ha-1 plus OEM injured corn. The amount of injury was different among sprayers, with the nozzle designs and arrangements responsible for corn injury. Injury was minimized when sethoxydim was applied with a sprayer equipped with 150 degree dual orifice nozzles spaced 38 cm apart and mounted on skids that contacted the soil to assure constant nozzle height. This sprayer, or sprayers of similar nozzle design, show the most potential for use by sweet corn growers.

Integrated weed management (IWM) is a component of integrated pest management (IPM), which is an interdisciplinary practice involving disciplines such as entomology, nematology, plant pathology, weed science, horticulture, agronomy, ecology, economics, and systems science. Most descriptions of IPM mention three elements: a) multiple tactics (for example, competitive varieties, cultural practices, herbicide usage) used in a compatible manner; b) pest populations maintained below levels that cause economic damage, and c) conservation of environmental quality. Integrated weed management was discussed in 1981 during a Weed Science Society of America (WSSA) Symposium entitled Integrated Weed Management Systems Technology for Crop Production and Protection. Topics presented included modeling weed biology, crop manipulation, biological control, herbicide technology, research needs, teaching approaches, and extension implementation. Our paper was presented as part of a symposium on IWM at the 1990 WSSA meeting. This paper describes some of the research that weed scientists have conducted during the past 40 yr. Topics examined include an introductory review of IPM, trends in several categories of weed research, goals and suggestions stated during the 1981 WSSA Symposium on IWM, IWM accomplishments since about 1981, and the future of IWM as a component of IPM.

A practical and objective system is needed to determine the lowest rates of the most efficacious herbicides to meet each producer's specific weed control problems. Determining which method of weed control to utilize is difficult today with increasing product choices, the growing use and complexity of herbicide mixtures, regulatory pressures to reduce rates, and the closer integration of weed control with other crop decisions. Expert computer systems could improve current practices and use herbicide mixtures as a tool to increase herbicide efficiency. Such systems would account for herbicide dose and mixture responses; select most economical herbicides; optimize adjuvants; recommend control at economic thresholds; and vary rates according to weed spectrum, density, and local environmental conditions. An example using chlorimuron and thifensulfuron illustrates how these systems could use quantitative dose response and mixture information.

The number of computer applications for purposes of weed control decisions has increased dramatically in the past eight yr. During this time, many efficacy-, and population-based weed control decision aids have been developed. The complexity of decisions range from those based on optimal weed control (independent of net profitability) to those predicting weed population effects before most profitable treatments are selected. While the number of software applications has increased sharply, national software databases have not been funded and tracking has been made difficult. The purpose of this paper is to review the criteria upon which efficacy- and population-based weed control decision aids are founded, and to identify software currently available in each of the two categories.

Tebuthiuron has been found in soils and plants a decade after application to rangelands in semi-arid areas. Forage production, length of growing season, and preference by grazing animals are greater on treated than on untreated areas. It is not understood how these differences occur. Blue grama forage was assayed for concentrations of N, P, K, Ca, Cu, Fe, Mg, Mn, and Zn in treated and untreated plants on adjacent paired plots in the field, 6 to 11 yr after tebuthiuron applications at three locations in Arizona. Only Fe and Mn concentration differed among treatments, being significantly higher (P = 0.05) in blue grama from treated plots.

A growing awareness of environmental issues in Canada has had a major influence on government policies. An initiative was launched by the government of Ontario to promote research toward the development of an integrated weed management (IWM) system. Research in IWM must take all aspects of the cropping system into consideration and evolve in a progressive manner. This approach must encompass the role of conservation tillage, knowledge of the critical period of weed interference, alternative methods of weed control, enhancement of crop competitiveness, modeling of crop-weed interference, influence of crop rotation and seed bank dynamics, and education and extension of the findings. The complexity involved in addressing these issues requires a multi-disciplinary approach.