The addition of a combination of methyl cellulose, sodium acetate and an alkyl aryl sodium sulfonate (sodium petroleum sulfonate) to spray solutions increased the toxicity of 2,2-dichloropropionic acid (dalapon) to oats and Cynodon dactylon L. The most effective combination tested on oats in the laboratory was 2.25% methyl cellulose, 1.75% sodium acetate, and 0.8% of an alkyl aryl sodium sulfonate. Lower concentrations of the three materials, combinations of any two of these additives, or any one added alone were less effective. Under field conditions, the response of Cynodon dactylon L. to dalapon was more rapid, control was more uniform and regrowth slower when dalapon sprays contained the three additives. Methyl cellulose increased and maintained the spray load on the grass foliage. Alkyl aryl sodium sulfonate probably increased penetration of dalapon. Sodium acetate increased the toxicity of the spray.

Selective postemergence spraying of cotton in the western irrigated areas for control of weeds has not been widely practiced because of the lack of adequate herbicides and little knowledge of the effect of varying rates of the more promising herbicides on the growth, yield and fiber quality of cotton.

In four field experiments, acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} applied preemergence at 1.1 kg/ha was not phytotoxic to peas (Pisum sativum L.) and increased the yield of shelled peas by an average of 25% compared to the weedy control. Yields were highest in all four experiments at the 1.1 kg/ha rate and tended to decline at higher rates of application. Growth chamber studies demonstrated that pea tolerance to acifluorfen was not affected by temperatures of 16/10 to 27/21C (light/dark) nor by stimulated rainfall of 0.5 to 5.0 cm. Peas and soybeans [Glycine max (L.) Merr.] were more tolerant of acifluorfen than were snap beans (Phaseolus vulgaris L.) and lima beans (Phaseolus lunatus L.) when acifluorfen was applied preemergence in the greenhouse or in hydroponic nutrient solution.

Field research to determine the influence of weed control systems in winter barley on subsequently no-till-planted grain sorghum was conducted from 1985 to 1987 in northwest Georgia. Herbicide treatments applied to fully tillered winter barley included 2,4-D, dicamba, metribuzin, oryzalin, oryzalin plus metribuzin, fluorochloridone, or thiameturon. None of these herbicides affected barley grain yields compared to nontreated plots. Treatments containing oryzalin reduced johnsongrass fresh weights in the subsequently planted grain sorghum. Oryzalin plus metribuzin, in 1 of 2 yr, resulted in higher seed yields of subsequently planted grain sorghum compared to the other treatments except for oryzalin used alone. Treatments containing paraquat plus propazine plus metolachlor applied to grain sorghum provided good weed control when averaged across barley treatments and resulted in the highest grain sorghum yield. No grain sorghum injury from herbicides used in the previous winter barley crop was observed.

Palmer amaranth (Amaranthus palmeri S. Watson) is a major biotic constraint in agronomic cropping systems in the United States. While crop–weed competition models offer a beneficial tool for understanding and predicting crop yield losses, within these models, certain weed biological characteristics and their responses to the environment are unknown. This limits understanding of weed growth in competition with crops under different irrigation methods and how competition for soil moisture affects crop growth parameters. This research measured the effect of center-pivot irrigation (CPI) and subsurface drip irrigation (SDI) on the actual evapotranspiration (ETa) of A. palmeri grown in maize (Zea mays L.), soybean [Glycine max (L.) Merr.], and fallow subplots. Twelve A. palmeri plants were alternately transplanted 1 m apart in the middle two rows of maize, soybean, and fallow subplots under CPI and SDI in 2019 and 2020 in south-central Nebraska. Maize, soybean, and fallow subplots without A. palmeri were included for comparison. Soil-moisture sensors were installed at 0-0.30, 0.30-0.60, and 0.60-0.90-m soil depths next to or between three A. palmeri and crop plants in each subplot. Soil-moisture data were recorded hourly from the time of A. palmeri transplanting to crop harvest. The results indicate differences in A. palmeri ETa between time of season (early, mid-, and late season) and crop type across 2019 and 2020. Although irrigation type did not affect subplot data, the presence of A. palmeri had an impact on subplot ETa across both years, which can be attributed to the variable relationship between volumetric soil water content (VWC) and ETa throughout the growing season due to advancing phenological stages and management practices. This study provides important and first-established baseline data and information about A. palmeri evapotranspiration and its relation to morphological features for future use in mechanistic crop–weed competition models.

Waterhemp [Amaranthus tuberculatus (Moq.) Sauer] is one of the most troublesome weeds in the United States. An A. tuberculatus population (CHR) was identified in Illinois, USA, as resistant to herbicides from six different site-of-action groups. Recently, the same population was also recognized as dicamba resistant. This study aimed to identify key resistance genes and the putative dicamba resistance mechanism in A. tuberculatus via transcriptomics analysis. Multiple differentially expressed (DE) genes and co-expression gene modules were identified as associated with dicamba resistance. Specifically, genes encoding glutathione S-transferases (GSTs), ATP-binding cassette transporters, peroxidases, and uridine diphosphate (UDP)-glycosyltransferases (UGTs) were identified. Results indicated enhanced oxidative stress tolerance as the primary mechanism for reducing dicamba toxicity. Results also point to potential glycosylation via UGTs and conjugation via GSTs of dicamba and its by-products. This is the first transcriptomics characterization of dicamba resistance in A. tuberculatus. Multiple non-target-site resistance genes were identified, indicating a cross-resistance pattern in the CHR population leading to a putative-enhanced oxidative stress response. Regions of multiple DE genes (i.e., genomic hot spots) across the A. tuberculatus genome corroborate previous results and potentially add to the complexity of non-target-site resistance traits.

Globe artichoke [Cynara cardunculus L. var. scolymus (L.) Fiori] is one of the most important crops across the Mediterranean basin, where weeds are an important biotic constraint limiting crop yields. However, the effects of globe artichoke–cropping systems on weeds have been rarely tested. Following the demand for eco-friendly weed management practices, a multi-location trial (13 farms) was carried out, measuring weed seedbanks and aboveground communities within four globe artichoke–cropping systems: globe artichoke monoculture (ART), past cultivation of globe artichoke (8 to 10 yr ago) (past-ART), a globe artichoke–durum wheat (Triticum durum Desf.) rotation (ART-WHEAT), and a control where globe artichoke was never grown. Both below- and aboveground weed communities were dominated by annual therophytes, but a low correspondence was found between both types of communities. Averaged over farms, ART highly reduced both the weed soil seedbank (1,600 seeds m−2 on average) and the aboveground weed biomass (only 3.4 g dry weight m−2) compared with the control, with a decrease of 72% in the soil seedbank and 99% in the aboveground flora. Moreover, on the farms where globe artichoke was previously grown, a very low aboveground weed biomass (77% less than control) was found. In addition, ART contributed to the preservation of high levels of weed diversity (except for aboveground communities) and therefore avoided the creation of a specialized weed flora. In conclusion, we suggest the inclusion of globe artichoke into crop rotation schemes in Mediterranean agroecosystems as a sustainable tool for reducing both the soil weed seedbank and aboveground weeds, thus reducing the requirement of direct weed control methods and preserving the environment.

False cleavers (Galium spurium L.) is an aggressive weed from the Rubiaceae. Here we assemble a chromosome-scale draft of its genome, laying the foundations for determining the genetic basis of auxinic herbicide resistance and for systematic research into its polyphyletic genus. We use the genome to examine the population genetics of material from the Canadian Prairies and, in concert with a common greenhouse experiment, to examine whether the phenotypic variation observed in the field results primarily from genetic or environmental factors. The genome assembly covers approximately 85% of G. spurium’s expected 360-Mbp genome size, with 94% of BUSCO (Benchmarking Universal Single-Copy Orthologs) genes complete and most single copy (89%). Approximately 37% of the genome is repetitive elements and 35,540 genes were annotated using RNA-seq data, including 100 homologues for genes involved in, or potentially involved in, herbicide resistance. The genome shows strong synteny with other members of the Rubiaceae, including smooth bedstraw (Cruciata laevipes Opiz) and robusta coffee [Coffea canephora (Pierre ex Froehner]. Double-digested RAD-seq data for the 19 populations from the Canadian Prairies indicated that G. spurium has high levels of population structure (FST = 0.54) and inbreeding (FIS = 0.86) with low levels of hetrozygosity (HO = 0.02) and nucleotide diversity (π = 0.0003). Variation in flowering time and seed weight largely overlapped among populations grown in the greenhouse. A redundancy analysis investigating genotype–phenotype associations showed few associations between single-nucleotide polymorphism (SNP) variation and these characteristics. In contrast, the majority of SNPs under selection were associated with mericarp hook density. This suggests that for most traits, environmental variation rather than genetic variation likely underlies phenotypic differences observed in the field. Several genes of interest, including several homologues involved in the assembly of the Skp1-Cullin-F-Box IR1/AFB E3 ubiquitin ligase complex (e.g., CAND1, ECR1), are located in areas of the genome with evidence of selection and are targets for further investigation.

The morphological and physiological response of the slender oat (Avena barbata Pott ex Link # AVEBA) to the herbicides barban (4-chloro-2-butynyl 3-chlorophenylcarbamate) and difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) in conjunction with decreased water availability was determined for seven populations, representing three ecotypes, under greenhouse conditions. Generally, within the range of sublethal herbicide doses, with increasing herbicide rates, phytotoxicity ratings increased, but plant dry weight, tiller height, and number of spikelets were decreased. Also, the number of juvenile tillers decreased, while that of fertile tillers increased. Flag leaf area increased and flowering was delayed. The ratio of number of spikelets to plant dry weight and seed weight was influenced the least. Under the highest rates of difenzoquat, the within-plant variance of spikelet number decreased, indicating that there may have been a more equal partitioning of resources amongst tillers for spikelet production. The general influence of water stress was to amplify the effect of the herbicide. For example, the dry treatment reduced dry weight and tiller height, and delayed flowering. Within a particular herbicide treatment, the effect of the water stress was to cause reduced within-plant variance for days to flowering, flag leaf area, and number of spikelets. Three reactions were observed that could have helped buffer decreases in spikelet production: 1) An increased fraction of the dry weight of the plants was partitioned into the spikelets at the expense of other vegetative matter, 2) the increased leaf area of the primary tiller may have helped counterbalance any reduction in photosynthesis caused by herbicide action, and 3) an increased number of juvenile tillers was converted into fertile tillers resulting in an increased number of mature tillers. These data indicate that the slender oat has a remarkable “phenotypic plasticity,” which enables it to maintain reproductive structures under sublethal herbicide doses.

Weed and cucumber (Cucumis sativus L. ‘Poinsett’) growth was studied where herbicides were soil-applied or applied to emerged weeds in the established crop. Cucumber yields were decreased at least 36% in 2 of 5 yr when weeds interfered for 4 weeks after emergence. Sequential applications of bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] applied preplant and incorporated (PPI) + trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) applied postemergence and incorporated (POI) were outstanding and controlled Japanese millet (Echinochloa crus-galli Link. var. frumentacea), Texas panicum (Panicum texanum Buckl.), Palmer amaranth (Amaranthus palmeri S. Wats.), and common purslane (Portulaca oleracea L.) without affecting the growth or yield of cucumber. Compared with bensulide, the selectivity of soil-incorporated butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] with cucumber was limited. Laboratory bioassays showed that under warm field soil conditions, PPI applications of 1.7 kg/ha of butralin persisted more than 2 months, but were dissipated after 4 months. Ethalfluralin [N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine] reduced cucumber yields only when it was soil-incorporated to the crop-seed depth at planting. Applications to soil of bensulide + DCPA (dimethyl tetrachloroterephthalate) stunted cucumber plants, reduced leaf area, increased leaf thickness, and caused higher near-infrared (0.75 to 1.34 μm) leaf reflectance.

Key metabolic enzymes and germination were studied in developing and mature, dormant and nondormant prickly sida (Sida spinosa L.) seeds. Isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, fructose-1,6-diphosphatase, and phosphofructokinase activities were determined in developing and mature prickly sida seeds. Developing seeds less than 7 days after anthesis and at 17 days or greater after anthesis were unable to germinate. The 7-day-old seeds lacked all but fructose-1,6-diphosphatase activity. The 17-day-old seeds demonstrated all enzyme activities but failed to germinate because dehydration had occurred and seeds were unable to imbibe sufficient water without an afterripening period. Comparison of enzyme activities of dormant and nondormant seeds on incubation showed that only glucose-6-phosphate dehydrogenase was considerably different within the first 8 h of incubation. Nondormant seeds had considerable glucose-6-phosphate dehydrogenase activity before germination (radical protrusion at 8 h), suggesting an active pentose phosphate pathway.

Emergence of sugarbeets (Beta vulgaris L. ‘MonoHy D2’) from soil was reduced by germinating kochia [Kochia scoparia (L.) Schrad. ♯ KCHSC] seed at densities greater than 1 seed/cm2 when the fungus Rhizopus sp. was present. Water-soluble exudates from germinated kochia seed did not influence Rhizopus growth in vitro or sugarbeet germination. Cell-free culture extracts of Rhizopus reduced sugarbeet germination and radicle elongation. There appeared to be an interaction between kochia and Rhizopus, but the responsible compounds were not identified.

Along the lower Coastal Plain, from the western panhandle of Florida to the Carolinas, lie approximately ten million acres of deep sands. In northwest Florida the sandhills support chiefly scrub oaks and wiregrass (Aristida stricta). Oaks are mainly turkey oak (Quercus laevis) and bluejack oak (Q. incana). Once an understory to longleaf pine (Pinus palustris), the scrub oaks gained dominance as heavy, indiscriminate logging removed the pines. Today only scattered pines remain, and the oaks and wiregrass prevent seed from these pines from restocking the area.

Six herbicides were applied to young stands of Kentucky bluegrass at weekly intervals in treatments beginning 5, 7, 9 and 11 weeks after seeding bluegrass. In both years the arsenical containing herbicides were effective when applications were started 7, 9 or 11 weeks after seeding. Applications started five weeks after seeding were unsuccessful in 1962 but gave excellent control in 1963. Reduced stands of Kentucky bluegrass and generally poorer crabgrass control were obtained with phenyl mercuric acetate than with the arsenicals.

Sweet corn (Zea mays L.) tolerance to dicamba and several other herbicides is due to cytochrome P450 (CYP)-mediated metabolism and is conferred by a single gene (Nsf1). Tolerance varies by CYP genotypic class, with hybrids homozygous for functional CYP (Nsf1Nsf1) being the most tolerant and hybrids homozygous for mutant CYP alleles (nsf1nsf1) being the least tolerant. The herbicide safener cyprosulfamide (CSA) increases tolerance to dicamba by stimulating the expression of several CYPs. However, the extent to which CSA improves the tolerance of different sweet corn CYP genotypic classes to dicamba is poorly understood. Additionally, the effect of growth stage on sweet corn sensitivity to dicamba is inadequately described. The objective of this work was to quantify the significance of application timing, formulation, and CYP genotypic class on sweet corn response to dicamba. Hybrids representing each of the three CYP genotypes (Nsf1Nsf1, Nsf1nsf1, nsf1nsf1), were treated with dicamba or dicamba + CSA at one of three growth stages: V3, V6, or V9. Across all timings, the nsf1nsf1 hybrid was the least tolerant to dicamba, displaying 16% higher crop injury levels 2 wk after treatment and 2,130 kg ha−1 lower ear mass yields compared with the Nsf1Nsf1 hybrid. The V9 growth stage was the most susceptible time for dicamba injury regardless of genotypic class, with 1.89 and 1,750 kg ha−1 lower ear mass yields compared with the V3 and V6 application timings, respectively. The addition of CSA to dicamba V9 applications reduced the injury from dicamba for all three genotypic classes; however, it did not eliminate the injury. The use of Nsf1Nsf1 or Nsf1nsf1 sweet corn hybrids along with herbicide safeners will reduce the frequency and severity of injury from dicamba and other CYP-metabolized herbicides.

The alkanolamine salt of 2,4-dichlorophenoxyacetic acid (2,4-D), the dimethylamine salt of 2,3,6-trichlorobenzoic acid (2,3,6-TBA), and the sodium salt of 2,3,6-trichlorophenylacetic acid (fenac), were evaluated in controlling witchweed and toxicity to corn on germinating seed in petri dishes, as preplan ting, preemergence, and postemergence treatments in the greenhouse and as preplanting, soil-incorporated treatments in the field. Corn roots were affected more than the shoots by each herbicide. Fenac and 2,4-D inhibited root growth of corn seedlings in petri dishes more than 2,3,6-TBA. Fenac was the most effective herbicide for control of witchweed and weedy grasses when applied as a preplanting, soil-incorporated treatment and controlled witchweed at rates which significantly increased corn yields. Applied preplanting, 2,4-D did not control witchweed and 2,3,6-TBA at rates which gave witchweed control equivalent to that obtained with fenac was toxic to corn.

Maximum activity of isocitric lyase (EC 4.1.3.1) was reached at 24 hr incubation of afterripened (nondormant) prickly sida (Sida spinosa L.) seed. Enzyme activity declined gradually with incubation times in excess of 24 hr. Actinomycin D (Act D) at 5 μg/ml had essentially no effect on 24-hr germination but inhibited development of isocitric lyase activity 83%. Cycloheximide (CH) at 10 μg/ml inhibited 24-hr germination of punctured seed only 7% but inhibited development of isocitric lyase activity 76%. Seed incubated in water 12 hr before being transferred to Act D at 5 μg/ml for an additional 12 hr did not escape sensitivity to the antibiotic. Isocitric lyase activity was inhibited when assayed at 24 hr total incubation. In the reverse experiment, seed incubated in Act D 12 hr before being transferred to water, isocitric lyase activity at 24 hr was not affected. Apparently prickly sida seed lacked a performed mRNA for isocitric lyase and transcription and translation of the mRNA occurred shortly after initiation of radicle protrusion (~8 hr).

It is indeed a real pleasure for me to have the opportunity to participate in this third meeting of the Weeds Journal of Weed Society of America. The years I spent in the Weed Investigations Section were among the most rewarding of my professional life.