Bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide], cyperquat (1-methyl-4-phenylpyridinium), and perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide} were evaluated for their potential use as postemergence herbicides for selective yellow nutsedge (Cyperus esculentus L.) control in Kentucky bluegrass (Poa pratensis L.) in field studies. High rates of these herbicides as single or split applications were effective and only slightly reduced verdure of Kentucky bluegrass, indicating excellent selectivity. In greenhouse studies perfluidone exhibited growth retardant properties. Shoot dry weight production was inhibited and root dry weight of treated plants was markedly reduced. These two factors are undesirable features for commercial sod production.

MSMA (monosodium methanearsonate) and DSMA (disodium methanearsonate) killed 27 to 90% of the broomsedge (Andropogon virginicus L.) plants when applied at 1.1 to 6.7 kg/ha in July. These rates did not reduce yields of smooth bromegrass (Bromus inermis Leyss.) or affect the density of Kentucky bluegrass (Poa pratensis L.) growing in association with the broomsedge.

Although similar in mode of action, 1,2-dihydroxybenzene (catechol) and 1,1′-dimethyl-4,4′bipyridinium ion (paraquat) at different levels were required to kill plants. Both chemicals were fast-acting, they both required light to be active, and herbicides that inhibit photosynthesis protected the plants temporarily against the action of both compounds. Paraquat and catechol had additive effects on black nightshade (Solanum nigrum L.) but not on redroot pigweed (Amaranthus retroflexus L.). Catechol protected redroot pigweed against the action of paraquat.

Uptake and movement of various herbicides and auxins by bean (Phaseolus vulgaris L.) petiole sections were studied. Isopropyl m-chlorocarbanilate (chlorpropham) was the most mobile of the compunds studied, followed in order of decreasing mobility by: indole-3-acetic acid (IAA), 3-amino-s-triazole (amitrole), (2,4-dichlorophenoxy)acetic acid (2,4-D), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), and 3-amino-2,5-dichlorobenzoic acid (amiben). Amiben immobilization may have been due to glucoside formation in the tissues. IAA was rapidly transported through basipetally but not acropetally oriented tissue. Tissue orientation had little effect on the movement of the other compounds. Mobility of the compounds studied, in general, appears to be a function of the amount of uncomplexed parent chemical. Retention is likely the result of conjugation with products in the cells or of physical binding in the cells.

Purple nutsedge (Cyperus rotundus L.) plants from tubers uniformly planted in fumigated soil were treated with 2,4-D [(2,4-dichlorophenoxy)acetic acid], paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), or dinoseb (2-sec-butyl-4-6-dinitrophenol). Repeated applications were made as required on the 1972 and 1973 plantings for one growing season. Emerged plants and their parent tubers were killed by four (1972) or five (1973) applications of paraquat. Three applications of 2,4-D were required for control in 1972. In 1973, a single treatment of 2,4-D afforded almost complete control. Three applications of dinoseb were required in 1972, but five were required in 1973.

Seeds of white spruce (Picea glauca, Moench), Colorado spruce (P. pungens, Engelm.), and Scotch pine (Pinus sylvestris L.) were treated with simazine in water at rates up to 1000 ppm for 20 hours, washed 10 min., rinsed twice, and sown. There was no effect on Colorado spruce or Scotch pine, but white spruce seeds were seriously affected above 250 ppm. Simazine has been considered not to affect seeds.

I am honored to meet here today with this distinguished group of scientists, engineers, educators and businessmen. I have looked forward to this conference as an opportunity particularly to discuss the problem of chemicals in our environment, a matter which concerns us all deeply … and to describe some of the steps we are taking in the Department in this regard. I also want to discuss our activities as they apply to the broader context of the responsibilities of science and education today in agriculture.

Pensacola bahiagrass (Paspalum notatum F.) is a leading pasture grass in the Southeastern and Gulf Coast states where it produces high quality forage on relatively infertile soils low in available moisture. It is a major seed crop on which many farmers rely as a cash crop. Weeds compete strongly with this grass during its establishment and even after establishment of a sod, various annual or perennial weed species may encroach. Control of such weeds often is desirable.

Zimmerman has summarized the plant hormone activity of trichlorobenzoic acid and various substituted derivatives. The effects have been found to be formative in nature.

The aim of this paper is to bring attention to weed ecology research that is taking place in an unexpected discipline: archaeology. While archaeobotanists (archaeologists or botanists who specialize in archaeological plant remains) have been accessing literature in weed ecology for decades and applying the findings to their own studies, their results are almost exclusively published in archaeological journals such as the Journal of Archaeological Science or Vegetation History and Archaeobotany. For this reason, their work is underutilized by weed ecologists, especially those who have an interest in historical weed ecology. Archaeobotanical research could help weed scientists understand the long-term effects of agricultural practices on weed communities and predict the potential impacts of climate change. This paper begins with a brief review of the history of archaeobotany as a discipline, then describes ways in which weed ecology is applied in archaeobotany, including Functional Interpretation of Botanical Surveys (FIBS). Finally, we present opportunities for future collaboration between archaeobotanists and weed scientists.

Herbicide resistance, documented in many economically damaging weed species, is a major threat to global crop production. The injudicious use of herbicides, often in the absence of diverse weed control strategies, poses an immense selection pressure on weed communities for resistance evolution and weed adaptive traits such as high seed dormancy. This study evaluates the interaction among developing herbicide resistance, seed size, and seed dormancy of ripgut brome (Bromus diandrus Roth), wild oat (Avena fatua L.), and hare barley [Hordeum leporinum Link; syn. Hordeum murinum L. ssp. leporinum (Link) Arcang.] collected from within intensively managed fields (in-crop) in comparison with populations in surrounding ruderal (non-crop disturbed) areas with no history of exposure to herbicides within the Western Australian grainbelt. Seed size of the three species varied by farming system (continuous cereal-intensive annual crops, diverse annual crops, pasture based) and habitat (in-crop, ruderal). Field populations of H. leporinum and B. diandrus tended to have greater seed size compared with ruderal populations. Larger seeds had significantly more dormancy in all three weed species. Field-collected populations that were exposed to herbicide applications for at least the past 5 yr exhibited significantly greater seed dormancy compared with their counterparts present in ruderal areas within the same geographic area. The association between increased seed dormancy and developing multiple herbicide resistance further complicates effective weed management.

One of the cultural practises used to control weeds in wheat fields is the application of 2,4-D sprays. The spray is applied as a post emergent selective after the wheat and the weeds have made some growth. The success of selective weed control in wheat depends upon the relative resistance of the wheat plants and the relative susceptibility of the weed plants to the 2,4-D spray. Major factors affecting successful weed control in wheat fields are the stage of growth of both wheat and weed plants, the quantity and formulation of 2,4-D applied, the solvent or carrier for the 2,4-D, the variety of wheat, and the species of weeds present.

Establishment of new seedings of alfalfa is often difficult because of the many hazards encountered during the first season of growth. In the Central Great Plains moisture is often the major factor determining the degree of success of the operation. This condition can be accentuated by the presence of a population of annual grasses such as the foxtails (Setaria spp.) and barnyard grass (Echinochloa crusgalli L. Beauv.). These grasses have a more rapid seedling growth rate than alfalfa and tend to produce a drouthy condition in the soil by rapid utilization of the available moisture. The same effect often results from the use of oats or other small grains as companion crops.

Photosystem II (PS II)-inhibitor herbicide resistance in Ontario waterhemp [Amaranthus tuberculatus (Moq.) Sauer] populations is conferred via target-site resistance (TSR) and non–target site resistance (NTSR) mechanisms. Metribuzin-resistant (MR) A. tuberculatus is due to TSR. Conversely, in other populations of PS II–inhibitor resistant A. tuberculatus, plants are resistant to atrazine but metribuzin sensitive (MS). The objective of this study was to determine the biologically effective dose of metribuzin applied preemergence and postemergence for the control of MS and MR A. tuberculatus. Ten field experiments were conducted in 2019 and 2020 to determine the effective doses of metribuzin for 50%, 80%, and 95% control of MS and MR A. tuberculatus. Metribuzin applied preemergence at the calculated doses of 133, 350, and 1,070 g ai ha−1 controlled MS A. tuberculatus 50%, 80%, and 95%, respectively, whereas the calculated doses of 7,868 and 17,533 g ai ha−1 controlled MR A. tuberculatus 50% and 80%, respectively, at 12 wk after application (WAA). Metribuzin applied postemergence at the calculated doses of 245 and 1,480 g ai ha−1 controlled MS A. tuberculatus 50% and 80%, respectively; the calculated dose for 50% MR A. tuberculatus control was greater than the highest dose (17,920 g ai ha−1) included in this study. Metribuzin at 560 and 1,120 g ha−1 and pyroxasulfone/flumioxazin (240 g ai ha−1) applied preemergence controlled MS A. tuberculatus 88%, 95%, and 98%, respectively, at 12 WAA, whereas the same treatments only controlled MR A. tuberculatus 0%, 4%, and 93%, respectively, at 12 WAA. Metribuzin at 560 and 1,120 g ha−1 and fomesafen (240 g ai ha−1) applied postemergence controlled MS A. tuberculatus 65%, 70%, and 78%, and MR A. tuberculatus 0%, 1%, and 49%, respectively, at 12 WAA. Based on these results, PS II–inhibitor resistant A. tuberculatus with NTSR (enhanced metabolism) is controlled with metribuzin applied preemergence and postemergence; in contrast, PS II–inhibitor resistant A. tuberculatus with TSR (glycine-264-serine altered target site) is not controlled with metribuzin.

Crabgrass, Digitaria sanguinalis (L.) Scop., is one of the most troublesome annual turf weeds over much of the United States. In the sub-tropical climate of Southern California its life cycle appears to be quite different from that in most of the United States. To the author's knowledge, its behavior in such a climate has not been described. Studies of its natural development here were conducted in 1959 and 1960.

Cotton seedlings emerged normally following applications of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) before or after furrowing for the preplanting irrigation, but 7 to 10 days after emergence stands were sometimes reduced when diuron was applied before furrowing. Stand reductions were most severe when cottonseed were planted at or above the layer of diuron-treated soil. Cotton varieties differed in tolerance to diuron. Preplanting applications controlled annual weeds until mid-season and treated cotton produced normal yields, except where stands were reduced. Fiber properties and boll components of treated cotton were not altered. Content of diuron was highest in young cotton plants. No diuron was found in cottonseed at harvest using an analytical procedure having a sensitivity of 0.1 ppm.

Amitrole (3-amino-1,2,4-triazole) is absorbed and actively bound to non-physiological sites in Salmonella typhimurium. Accumulation of amitrole is inhibited by purines; but the effect does not seem to explain adenine protection against growth inhibition by amitrole. Guanine, xanthine, and hypoxanthine cannot replace adenine in growth protection but do inhibit accumulation of amitrole in the bacterial cells.

Russian thistle (Salsola tragus L.) is among the most troublesome weeds in cropland and ruderal semiarid areas of the Pacific Northwest (PNW). Predicting S. tragus emergence timing plays a critical role in scheduling weed management measures. The objective of this research was to develop and validate a predictive model of the seedling emergence pattern of S. tragus under field conditions in the PNW to increase the efficacy of control measures targeting this species. The relationship between cumulative seedling emergence and cumulative hydrothermal time under field conditions was modeled using the Weibull function. This model is the first to use hydrothermal time units (HTT) to predict S. tragus emergence and showed a very good fit to the experimental data. According to this model, seedling emergence starts at 5 HTT, and 50% and 90% emergence is completed at 56 HTT and 177 HTT, respectively. For model validation, independent field experiments were carried out. Cumulative seedling emergence was accurately predicted by the model, supporting the idea that this model is robust enough to be used as a predictive tool for S. tragus seedling emergence. Our model can serve as the basis for the development of decision support systems, helping farmers make the best decisions to control S. tragus populations in no-till fallow and spring wheat systems.

Terbacil (3-tert-butyl-5-chloro-6-methyluracil) was applied to highbush blueberry plants (Vaccinium corymbosum L. ‘Pemberton’, ‘Rancocas', ‘Jersey’, and ‘Concord’) growing in a Rifle peat, Camas clay loam, or Mossy Rock silt loam for control of quackgrass [Agropyron repens (L.) Beauv.]. Control was 80 to 100% from applications made in April after the blueberry plants broke dormancy. Higher dosages proved phytotoxic from these applications on Camas clay loam. Applications in February or March while the blueberry plants were still dormant caused no phytotoxicit; to the blueberry plants and provided 80 to 90% quackgrass control. Four consecutive yearly applications caused no residual buildup to the point of phytotoxicity to blueberry plants. Carry-over of terbacil in the soil from year to year did occur.

Field studies were established in 1974 and 1975 at various locations in San Diego County, CA, to evaluate several herbicides for the control of chamise (Adenostoma fasciculatum H.&A.) and redshank chamise (Adenostoma sparsifolium Torr.). Herbicide effects on vegetation were reevaluated in 1982. Plots originally treated with 2.2 or 4.5 kg ae/ha of glyphosate [N-(phosphonomethyl)glycine] had virtually no chamise regrowth 8 yr after treatment. The herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid], combinations of 2,4-D with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] or dichlorprop [2-(2,4-dichlorophenoxy) propionic acid], fosamine [ethyl hydrogen (aminocarbonyl)phosphonate], triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and picloram (4-amino-3,5,6-trichloropicolinic acid) had no long-term effects on chamise. Soil collected in 1982 from glyphosate-treated plots contained similar numbers of chamise seeds but fewer seeds of other species compared to untreated plots. Canopy cover of redshank chamise was similar in treated and untreated plots after 8 yr. These results document the effectiveness of glyphosate in killing the underground root-crown of chamise, which prevented sprouting, but not redshank chamise.