Foliar application of herbicides, plant regulators, and nutrients is a well established practice. Yet, the many contradictory reports in the literature (7) indicate that the routes of entry into and movement within leaves are not clearly known. This situation has probably arisen because presently available techniques do not precisely establish the location of the penetrant on the cellular level.

Corn poppy (Papaver rhoeas L.) is the most widespread broadleaf weed species infesting winter cereals in Europe. Biotypes that are resistant to both 2,4-D and tribenuron-methyl, an acetolactate synthase (ALS) inhibitor, have evolved in recent decades, thus narrowing the options for effective chemical control. Though the effectiveness of several integrated weed management (IWM) strategies have been confirmed, none of these strategies have been tested to manage multiple herbicide–resistant P. rhoeas under no-till planting. With the expansion of no-till systems, it is important to prove the effectiveness of such strategies. In this study, a field experiment over three consecutive seasons was conducted to evaluate and compare the effects of different weed management strategies, under either direct drilling (i.e., no-till) or intensive tillage, on a multiple herbicide–resistant P. rhoeas population. Moreover, evaluations were carried out as to whether the proportions of ALS inhibitor–resistant individuals were affected by the tillage systems for each IWM strategy at the end of the 3-yr period. The IWM strategies tested in this research included crop rotation, delayed sowing, and different herbicide programs such as PRE plus POST or POST. All IWM strategies greatly reduced the initial density of P. rhoeas each season (≥ 95%) under either direct drilling or intensive tillage. After 3 yr, the IWM strategies were very effective in both tillage systems, though the effects were stronger under direct drilling (~95%) compared with intensive tillage (~86%). At the end of the study, the proportion of ALS inhibitor–resistant plants was not different between the IWM strategies in both tillage systems (94% on average). Therefore, crop rotation (with sunflower [Helianthus annuus L.]), delayed sowing, or a variation in the herbicide application timing are effective under direct drilling to manage herbicide-resistant P. rhoeas. Adoption of IWM strategies is necessary to mitigate the evolution of resistance in both conventional and no-till systems.

Greenhouse and field experiments were conducted to study competition between wheat and rigid ryegrass or between wheat and cowcockle using additive series and growth analysis. Wheat was the dominant competitor with either weed. One wheat plant was as competitive as 1 1 or 19 rigid ryegrass plants in greenhouse and field experiments, respectively. One wheat plant was as competitive as three to 24 cowcockle plants, depending on environmental conditions. Dry weight of roots, leaves, stems, and spikes or capsules responded similarly to the effects of competition between wheat and rigid ryegrass or cowcockle. Shoot dry weight was the easiest, fastest, and least expensive component to measure competition. Growth analyses of individual plants showed that wheat had a greater leaf area, shoot and root dry weight, and absolute growth rate than rigid ryegrass or cowcockle, particularly early in the season. A range of 120 to 240 wheat plants m−2 can minimize rigid ryegrass or cowcockle competition and achieve an acceptable grain yield in semiarid areas in Morocco.

The increasing use of toxic agents as pesticides for application contiguous to water areas has been viewed with trepidation by many fisheries workers. Herbicidal chemicals are viewed with particular alarm due to their increased use, both present and projected, for the control of aquatic vegetation where they are placed in direct contact with fish and other aquatic organisms.

Rough pigweed (Amaranthus retroflexus L.) on the average emerged 2 days earlier than yellow foxtail (Setaria glauca (L.) Beauv.) The heading and maturity of both weeds seeded in corn was delayed for 3–4 days. The interval between emergence and maturity decreased progressively as seeding dates were delayed. The tallest plants and the highest yields were produced from the early spring seedings. Competition from corn depressed yields of both weeds more than their heights. Height and yield of foxtail seeded during July were most affected. In later seedings foxtail tolerated corn competition much better than pigweed.

Field bindweed (Convolvulus arvensis L.) is a persistent, perennial weed species that infests a variety of temperate habitats around the globe. To evaluate the efficacy of general management approaches and impacts on crop yield and to identify research gaps, we conducted a series of meta-analyses using published studies focusing on C. arvensis management in annual cropping and perennial systems. Our analysis of 48 articles (560 data points) conducted in annual systems indicated that 95% of data points measured efficacy over short time frames (within 2 yr of treatment). Furthermore, only 27% of data points reported impacts of C. arvensis management on crop yield. In annual systems, herbicide control dominated the literature (~80% of data points) and was an effective management technique up to 2 yr posttreatment. Integrated management, with or without herbicides, and three nonchemical techniques were similarly effective as herbicide at reducing C. arvensis up to 2 yr posttreatment. In addition, integrated approaches, with or without herbicides, and two nonchemical techniques had positive effects on crop yield. There were few differences among herbicide mechanism of action groups on C. arvensis abundance in annual systems. There were only nine articles (28 data points) concerning C. arvensis management in perennial systems (e.g., pasture, rangeland, lawn), indicating more research effort has been directed toward annual systems. In perennial systems, biocontrol, herbicide, and non-herbicide integrated management techniques were equally effective at reducing C. arvensis, while competition and grazing were not effective. Overall, our results demonstrate that while chemical control of C. arvensis is generally effective and well studied, integrated and nonchemical control practices can perform equally well. We also documented the need for improved monitoring of the efficacy of management practices over longer time frames and including effects on desired vegetation to develop sustainable weed management programs.

An effective management plan for invasive herb populations must consider the potential for regeneration from the soil seedbank. To test this potential, we examined two species, Japanese stiltgrass and garlic mustard, at deciduous forest sites in southeastern Ohio. Seeds were buried in nylon mesh bags and recovered at regular intervals over 24 mo. Recovered seeds were tested for germination and viability. Burial was replicated on north- and south-facing slopes to test for environmental control of dormancy state. Stiltgrass seeds experienced severe mortality in the soil, rarely surviving the full 24 mo. Stiltgrass showed fractional germination in the lab ranging from 86% to 89% of viable seeds in late spring (the season of natural seedling emergence) to complete nongermination in winter. Most garlic mustard seeds survived through the experimental period (82% and 88% survival across 24 mo) with consistently low mortality (0% to 13%) unrelated to season. Slope aspect had no significant effect on survival or dormancy state in either species. Extrapolation of garlic mustard mortality implies that reproduction would need to be suppressed for a substantial period (perhaps >10 yr) to ensure eradication of a population. In stiltgrass, rapid seed mortality suggests that control can be achieved in 2 to 4 yr.

Studies were conducted to determine the effect of simulated rainfall on the phytotoxicity of several herbicides. Oil soluble herbicides 4,6-dinitro-o-sec-butylphenol (DNBP), pentachlorophenol (PCP), a 1:1 mixture of the butyl esters of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid (2,4-D: 2,4,5-T), and a 2:2:1 mixture of the isooctyl esters of 2,4–13:2,4,5-T: 4-amino-3,5,6-trichloropicolinic acid (picloram) (hereinafter referred to as M-3140), usually were less affected by artificial rainfall than were water soluble 1,1'-dimethyl-4,4'-bipyridinium salt (paraquat), dimethylarsinic acid (cacodylic acid), and cis-2,3,5,5,5-pentachloro-4-ketopentenoic acid (hereinafter referred to as AP-20), on guava (Psidium guajava L.) and mango (Mangifera indica L.). Washing reduced the activity of some oil and water-soluble herbicides on sorghum (Sorghum bicolor (L.) Moench, var. Combine Kafir-60) and dioscorea (Dioscorea composita Hemsl). As herbicide rates were increased, washing reduced the phytotoxicity of paraquat and 2,4-D:2,4,5-T less on mango and guava. Artificial rainfall applied as a mist spray at different intervals had no effect on the phytotoxicity of paraquat; it reduced the activity of cacodylic acid and increased the effectiveness of AP-20 on mango.

Millions of acres in the United States are being chemically treated each year for the control of weeds. Weed investigators have generally accepted the fact that certain herbicides affect certain plants to a greater degree than others. Because of this, numerous chemicals are being used. Except for 2,4-D, there has been little work done on the bactericidal and bacteriostatic properties of the recent herbicidal compounds. It is the purpose of this paper to report a study of the influence that several recommended and experimental herbicides have on the microbial activity of the soil population and to establish the usefulness of a simple procedure outlined by Nelson in making preliminary determinations of this type.

Astragalus miser Dougl., var. oblongifolius (Rydb.) Cronq. was analyzed for seasonal and physical distribution of its contained poison. Small chickens (Gallus domesticus, Arbor Acre X Vantress hybrids) and cattle (Bos taurus, Hereford) were used as test animals. The poisonous compound was extracted from dried plants with 95% ethanol, evaporated and redissolved in water, then semi-purified by several extractions with chloroform for toxicological studies. The poison was found primarily in the green leaves. The plants were very poisonous until they began drying in August. Once leaves became bleached at senescence, toxicity disappeared. Plants treated with the triethylamine salt of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and the alkyl amine salts of 2-(2,4,5-trichlorophenoxy)-propionic acid (silvex) were less poisonous to cattle than untreated plants. Acute poisoning in chickens was characterized by depression, accelerated heart action, followed by congestion of lungs, cardiac insufficiency, paralysis, and heart failure. Chronically poisoned birds exhibited the same syndrome but sustained more severe liver damage.

We examined the relationship between temperature and emergence of yellow nutsedge tubers to generate predictive models for the arid southwestern United States. Field experiments were conducted in California and Arizona to obtain phenological and temperature data needed to generate degree-day models. The effect of air temperature on emergence was tested with available programs using four methods to calculate degree-days (single sine, double sine, single triangle, and double triangle). Separate models were tested for each genotype examined (Arizona source and California source) as no one model was a good predictor of emergence when data were pooled. Results indicate that there is year to year variation in model accuracy but predictions of date of emergence can be made to within 2 d of actual emergence. This information can be used to schedule cultivations to reduce early yellow nutsedge competition in the field.

Glufosinate efficacy was examined in two major grass weed species, rigid ryegrass and sterile oat. Dose–response pot experiments under controlled environmental conditions showed that sterile oat was more successfully controlled by glufosinate than was rigid ryegrass. Glutamine synthetase was extracted from both species and assayed in vitro. Glufosinate readily inhibited glutamine synthetase activity in both species, indicating no differential sensitivity to the target enzyme. Thin-layer chromatography analysis of glufosinate showed no significant metabolism of glufosinate in either species. Absorption and translocation studies with 14C-glufosinate showed that the radiolabel was rapidly absorbed into the leaves of both species. However, translocation of radiolabeled glufosinate from the treated leaf to the meristematic regions was significantly greater in sterile oat, whereas translocation to the tip of the leaf was significantly greater in rigid ryegrass. This indicates that there is a difference in glufosinate distribution between the two species. It is likely that this difference in the distribution of glufosinate results in sterile oat being more easily controlled by glufosinate than is rigid ryegrass.

Toadflax invasion into natural areas has prompted interest in weed management via biological control. The most promising biological control agent currently available for the control of Dalmatian toadflax is Mecinus janthinus, a stem-boring weevil that has been shown to significantly reduce toadflax populations. Some land managers, however, are reluctant to release approved weed biological control agents based on concerns about possible nontarget impacts. Few postrelease examinations of biocontrol impact and host specificity have been performed, despite the call for such information. This study examined the host specificity of Mecinus janthinus, postrelease, in relation to Colorado sites to provide information to managers about its relative safety as a weed biological control agent. This study employed three components: (1) greenhouse choice and no-choice experiments; (2) no-choice caged field experiments; and (3) release-site evaluation of nontarget use of native plant species where this weevil has been released and has established. Both greenhouse and field experiments failed to demonstrate nontarget use of native plant species by M. janthinus in the region where it was studied, even in no-choice starvation tests. We found no evidence of nontarget herbivory on native plants growing at toadflax sites where M. janthinus was well established. These results support the continued use of M. janthinus as a low-risk biological control agent for the management of toadflax in the Rocky Mountain Front Range.

Early spring spray applications of the potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram) and certain formulations of 1:1 mixtures of picloram plus (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) controlled yaupon (Ilex vomitoria Ait.). Ester formulations of picloram or picloram plus 2,4,5-T were ineffective. Combinations of surfactant and oil: water carriers usually did not improve herbicide performance over water carriers. Granular picloram was superior to sprays when applied as soil treatments at equal rates and controlled yaupon at most dates of application. Post oak (Quercus stellata Wangenh.) and blackjack oak (Quercus marilandica Muenchh.) were controlled more effectively by picloram or picloram plus 2,4,5-T sprays on the foliage than by granular picloram as a soil treatment. Picloram granules usually killed winged elm (Ulmus alata Michx.) regardless of date of application.

Seeds of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] planted immediately after extraction from mature seed pods germinated 84% and after burial overwinter germinated 97%. Seedling emergence was limited to depths of less than 4 inches. Seedling roots developed adventitious buds capable of producing new shoots about 5 weeks after emergence. Preemergence and early postemergence treatments with 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) gave 100% control of seedlings in greenhouse experiments. Heavy natural infestations of honeyvine milkweed in corn (Zea mays L.) were controlled 95% with 2,4-(dichlorophenoxy)acetic acid (2,4-D) at 0.5 lb/A when treatments were made before the weed started climbing on corn stalks. Later treatments required higher rates of 2,4-D, the use of 2,4,5-(trichlorophenoxy)acetic acid (2,4,5-T), or the combination of 2,4-D plus 2,4,5-T for adequate control.

Residue levels of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} in soil were determined indirectly by measuring the chlorophyll content of wheat (Triticum aestivum L.) grown on a Norfolk sandy loam (Typic paleudult; fine loam, siliceous, thermic) 14, 22, 39, and 66 days after a preemergence application of the herbicide. The half-life for 0.22 and 0.45 kg/ha of fluridone was estimated to be 18 days. Phytotoxicity increased with increasing pH in newly-treated soils and in soil sampled 14 days after treatment. Higher chlorophyll levels in wheat grown in soil sampled 39 days after fluridone application indicated a decrease in biologically-active herbicide. Soil removed from the field following later cultivation produced small reductions in chlorophyll at pH 4.0 and 5.2, but at pH 7.0 significant fluridone activity was still present in the soil after 66 days. Cultivation may have increased the surface concentration of the herbicide.

Field pennycress (Thlaspi arvense L.) was seeded in rows at approximately 10-day intervals from June 1 to August 30, 1963, and from July 12 to August 31, 1966, in subarctic, south-central Alaska (61.5° N.). Plants from June 20 and earlier seedings produced mature seed as summer annuals; those from seedings during the first 3 weeks of July produced elongated stems and green pods, while those from later seedings produced unelongated, basal rosettes. Seedlings that emerged during July or later were potential winter annuals. No study plants survived the 1963-64 winter. The 1966 plantings survived the 1966-67 winter as follows: July 12, 50%, July 20, 54%, August 1, 93%, and August 12, 23, and 31, 100%. Morphology, time of flowering, and seed pod production of plants surviving the winter also were influenced by planting date the previous growing season. To prevent field pennycress from producing seed as a summer annual, plants that emerge before the middle of July must be eradicated. Plants that emerge during July or later should be destroyed as seedlings or prior to seed production time the following year.

The aryloxyphenoxypropionate and cyclohexanedione herbicides, which inhibit acetyl-coenzyme A carboxylase (EC 6.4.1.2), have also been hypothesized to act at specific sites on the plasmalemma. An impermeant sulfhydryl binding agent was reported to block the diclofop acid-induced depolarization of the membrane potential (Em) in rigid ryegrass. A correlation between the antagonistic interaction with auxin herbicides both in the field and in the Em response, and the repolarization of Em in herbicide-resistant rigid ryegrass following removal of diclofop acid also provide support for this hypothesis. However, similar membrane responses in resistant grasses and broadleaf species suggest that the membrane response may not be important in the phytotoxic activity of the postemergence graminicides under field conditions. In addition, an antagonistic interaction was not observed in roots of susceptible grasses exposed to combinations of diclofop-methyl and 2,4-D. Furthermore, the repolarization of the Em in diclofop-resistant rigid ryegrass was correlated to differential acidification of the external solution and an increase in the protonated form of diclofop acid, rather than a site-specific interaction at the plasmalemma. Although the membrane response is probably not involved in herbicide phytotoxicity in agricultural systems, a higher extracellular pH in the resistant biotypes of rigid ryegrass may inhibit the movement of these weak-acid herbicides across the plasmalemma, and possibly contribute to increased herbicide tolerance.

Crop and weed competition studies rarely determine how plant-to-plant interactions alter the structure and physiology of crop roots. Soybean has the ability to detect neighboring weeds and to alter growth patterns including the allocation of resources to root growth. In this study, we hypothesized that low red : far red light ratio (R : FR) reflected from aboveground vegetative tissue of neighboring weeds would alter soybean root morphology and reduce root biomass and nodule number. All experiments were conducted under controlled conditions in which resources of light, water, and nutrients were nonlimiting. Low R : FR reflected from aboveground neighboring weeds reduced soybean seedling root length, surface area, and volume, including the number of nodules per plant. An accumulation of H2O2, an increase in malondialdehyde (MDA) content, a reduction in flavonoid content, and a decrease in 1,1-diphenyl-2-picrylhydrazyl (DPPH)–radicle scavenging activity were observed. The reduction in flavonoid content was accompanied by a decrease in the transcription of GmIFS and GmN93 and an increase in transcript levels of several antioxidant genes. These molecular and physiological changes may have a physiological cost to the soybean plant, which may limit the plant's ability to respond to subsequent abiotic and biotic stresses that will occur under field conditions.

Management practices and cropping systems that serve as integrated weed management practices, and at the same time can contribute to improved soil quality, will be important for the sustainability of agricultural production systems. The objective of this study was to assess weed species population density under contrasting tillage (conventional tillage [CT] and no tillage [NT]), residue burning (burn and no burn), and residue level (low and high) treatments after 5 and 6 yr of consistent management in a wheat–soybean double-crop production system. A field experiment was conducted from fall 2001 to fall 2007 in the Mississippi River Delta region of eastern Arkansas on a Calloway silt–loam. Weed assessments were conducted twice during the soybean growing season, before (early season) and after herbicide application (late season) in 2006 and 2007. Total weed density was greater under CT (513 plants m−2) than under NT (340 plants m−2) early in the growing season in 2006, but was greater under NT than CT late in the season in 2007, suggesting that the effectiveness of glyphosate on total weeds differs between CT and NT. Averaged across residue levels, grass species density was greatest in the NT–burn (68 to 167 plants m−2) combination and lowest in the NT–no-burn (41 to 63 plants m−2) early in the growing season in both years. Broadleaf density was greater early (200 to 349 plants m−2) than late (18 to 20 plants m−2) in the growing season under both CT and NT in 2006, but in 2007 broadleaf density did not differ by tillage treatment between seasons. Perennial weed density was greater in the burn (99 plants m−2) than in the no-burn (59 plants m−2) treatment in 2006. No tillage, no burning, and a high residue level appeared to contribute to the suppression of most weed species without reducing herbicide efficiency.