Field experiments were established to observe the effects of adjuvants and time of application on weed control and ‘Terra-Vig 515’ soybean tolerance with POST applications of AC 263,222. A nonionic surfactant or a crop oil concentrate increased sicklepod control with AC 263,222 applied at either V2 or V6 soybean growth stages. Sicklepod control increased as AC 263,222 was increased from 35 to 70 g ai ha–1 only when applied without an adjuvant. Late in the season, there was no difference in sicklepod control between V2 and V6 applications. Adjuvants and application timing within herbicide treatments had no effect on pitted morningglory control, and, though adjuvants increased common cocklebur control, all treatments controlled more than 85% of both species. AC 263,222 with adjuvants at all rates and timings injured and stunted soybean more 2 wk after treatment compared to AC 263,222 alone. AC 263,222 at 35 or 70 g ha–1 with crop oil concentrate reduced yields more than AC 263,222, with either a surfactant or no adjuvant when applied to V2 soybeans.

Application of crop protection compounds to randomized small plots with motorized sprayers can be a cumbersome process for field researchers. A motorized, high clearance spraying system has been developed that allows precise application of spray mixtures to randomized plots without driving along alleys between blocks or changing sprayate bottles between treatments. A description of the spraying system is given.

Formulations of fenoxaprop enriched in the R(+) isomer, HOE 46360-08H EW (described as an emulsifiable water-based formulation) and HOE 46360-05H EC (emulsifiable concentrate), were compared with the commercial racemate EC for control of roughstalk bluegrass and tolerance of perennial ryegrass and tall fescue grown for seed. The enriched EW and EC formulations were more than twice as active as the racemate per kg total fenoxaprop, despite enrichment to only 92 and 89% R(+) isomer purity, which should have increased activity by 1.84- and 1.78-fold, respectively. Increased activity was evident both as improved weed control and as decreased crop tolerance. Although the 3.69-fold increase in activity of HOE 46360 EW on roughstalk bluegrass relative to the racemate may be partly due to changes in the emulsion, the 3.06-fold increase in activity of HOE 46360 EC suggests that the S(-) isomer somehow interferes wih the activity of the R(+) isomer. Use of 280 g ai ha–1 of the racemate could be replaced with 76 g ha–1 of the EW or 92 g ha–1 of the EC formulation of HOE 46360 for equivalent roughstalk bluegrass control, but with decreased crop tolerance in perennial ryegrass and tall fescue.

Eight field studies were conducted in soybeans at seven locations in Kansas over a 3-yr period to examine the efficacy of using reduced rates of the herbicides acifluorfen, bentazon, chlorimuron, and tank mixes of acifluorfen and bentazon. POST applications of these herbicides at 1/2X rates at 2 wk after planting (WAP) resulted in broadleaf weed control similar to that obtained from standard treatments of 1X rates applied at 4 WAP at six of seven studies with acifluorfen, bentazon, and acifluorfen plus bentazon and at five of seven studies with chlorimuron. One-quarter rates applied 2 WAP were equivalent to standard treatments for broadleaf weed control in four of seven studies with acifluorfen and chlorimuron, five of seven studies with bentazon, and six of seven studies with acifluorfen plus bentazon. One cultivation at 4 WAP, increased the broadleaf weed control with all herbicide treatments.

Field studies were established to evaluate several herbicides for buckbrush control in tall fescue pastures. Buckbrush was controlled most consistently by 2,4-D amine or low volatile ester, or package-mixes of 2,4-D plus dicamba or triclopyr. Two consecutive years of herbicide application was more effective for reducing buckbrush stem populations than one application.

Lack of consistent weed control has been a major limiting factor in the adoption of no-till soybean production. Field studies were conducted at Waseca, MN from 1987 through 1990 to evaluate the efficacy of imazethapyr applied either alone or in combination with other herbicides for weed control in no-till soybean. Fall applications of imazethapyr did not provide acceptable weed control. Imazethapyr applied 2 to 4 wk before planting provided a weed-free seedbed whereas burndown treatments applied 1 to 3 d before planting failed to do so. Early preplant imazethapyr applied during the second week of April did not control weeds as well as imazethapyr applied during the last week of April. Imazethapyr applied alone PRE failed to control weeds adequately. A split application of early preplant plus PRE imazethapyr resulted in excellent weed control, especially when metribuzin was added with each application. Imazethapyr is a promising herbicide for weed control in no-till soybean production.

The critical weed-control period in field seeded cabbage using natural weed stands was 2 wk in 1988 and 4 wk in 1989. Regression analysis showed that the length of weed-free period, weed density, and ambient light reduction by competing weeds were factors affecting cabbage yield. Weeds that emerged after the initial weed-free period shaded the soil and subsequently lowered soil surface temperatures in 1989. Velvetleaf densities of 1.2 and 3.6 plants per m2 that competed all season with cabbage reduced cabbage yields 52% and 71% of the weed-free treatment in 1988 and 76% and 92% in 1989, respectively. Cabbage yields were reduced at all velvetleaf densities seeded 0, 1, and 2 wk after cabbage, but cabbage yield was not reduced when velvetleaf was seeded 4 or 6 wk after cabbage. Cabbage yield was not different between parallel and staggered velvetleaf configurations at 0.6 plants per m2, but was reduced with longer periods of competition. Velvetleaf seed production was prevented with 6 wk weed-free period after cabbage emergence and subsequent destruction of emerging velvetleaf after cabbage harvest.

The efficacy of herbicides applied broadcast by hand with a soil carrier or sprayed with water carrier were compared for Italian ryegrass control in winter wheat in central Oklahoma. Italian ryegrass was controlled 77 to 100% with BAY SMY 1500, chlorsulfuron, and CGA-131036 applied with both carriers. Metribuzin applied POST with 187 L ha–1 water was less phytotoxic to Italian ryegrass and wheat than with 200 kg ha–1 soil. All herbicides applied with 200 kg ha–1 silt loam soil as carrier at two locations controlled Italian ryegrass 96 to 100%. Increasing herbicide rate, soil carrier quantity, or broadcasting soil-carried herbicide in two directions rather than one did not significantly improve herbicide efficacy over that of conventional spraying.

The effects of topsoil thickness on winter annual weed growth and nutrient concentration were assessed for three consecutive years in soybean plots. The topsoil treatments had high fertility levels, uniform textures, and no herbicides were used in the study. Common chickweed composed 75% of the winter annual weed species. Weed biomass production decreased as topsoil thickness decreased from 22.5 cm to 0. Topsoil thickness of 22.5 cm produced 800 kg ha–1 more weed growth than 0 cm topsoil. The weed biomass grown in thicker topsoil had higher total amounts of N, K, Mg, and Ca.

Research was conducted to determine the tolerance of flue-cured tobacco to fomesafen and the potential for weed control in tobacco with fomesafen. Treatments consisted of fomesafen at 0.4 or 0.6 kg ai ha–1 applied pretransplant incorporated (PTI), pretransplant (PRE-T), post-transplant (POS-T), postemergence-over-top (POT), or post-directed (PD). Tobacco injury within 30 d of application was as high as 30%, but tobacco recovered and few significant differences in tobacco yield, grade index, or price were observed except where fomesafen was applied PTI at 0.6 kg ha–1. Tobacco tolerance relative to time of application was generally PRE-T = POT > POS-T = PTI. Florida pusley and large crabgrass control was > 80% for all fomesafen treatments. Yellow and purple nutsedge control was approximately 30% before cultivation.

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.

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.

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.

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.

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 herbicide 2,4-D has been in commerce and a subject for research since 1944. It is undoubtedly among the most thoroughly researched pesticides in the world. In our society, 2,4-D has played an indispensable role. It is most important in the production of our food and fiber; in the control of noxious weeds causing public health problems such as common ragweed (Ambrosia artemisiifolia L.) and poison-ivy [Toxicodendron radicans (L.) Ktze.] in the maintenance of our utility supply lines and highway and railroad systems; and as a useful tool for creating desirable wildlife habitats and beautifying our parks, golf courses, and the grounds about our homes.

Recently completed toxicological studies support the conclusions of earlier studies that 2,4-D may be used without undue risk to man, wildlife, or the environment. This does not mean, of course, that we should lessen our precautions to avoid exposure to applicators, prevent spray drift from getting on bystanders, or on pets such as dogs and cats, and following general good sanitation practices in its use.

There have been some reports of an association between the use of 2,4-D and NHL. However, in our opinion after considering all the toxicological and epidemiological evidence, it has not been established that the use of 2,4-D causes NHL or any other type of cancer including soft tissue sarcomas and Hodgkin's disease. As cited in this review, most scientific experts who have carefully examined all the data share this opinion.