A recent paper (Shields et al. 2006) reports trapping seed of horseweed in the planetary boundary layer (PBL) of the lower atmosphere at heights up to 140 m above ground level. While it claims that seeds have not been trapped from the PBL before, it is shown here that seeds of other weedy composites were trapped at altitudes up to 610 m above ground level in southern Australia more than 40 yr ago.

Timely results from whole-plant, herbicide-resistant weed screenings are crucial to heighten grower awareness. However, the high degree of physiological dormancy of giant ragweed (Ambrosia trifida L.) seed exacerbates this process. The most effective methods for alleviating dormancy, to date, are either labor-intensive (embryo excision) or require several weeks (soil stratification). This research describes a conditioning process involving clipping and aeration of seed in water that is highly effective at alleviating dormancy and requires less skill and time compared with previous techniques. Ambrosia trifida seeds were collected over 2 yr at two different collection timings (September 25, “early”; October 25, “late”), subjected to various treatments intended to release dormancy, and evaluated for emergence over 18 d in the greenhouse. The use of germination-promoting chemicals (ethephon, gibberellic acid, and thiourea) generally provided no increase in emergence compared with water and occasionally produced seedlings with abnormal growth unsuitable for further experimentation. Conditioning yielded between 30% and 33% emergence for both early and late collections of seeds with no afterripening period compared with 0% emergence for seeds imbibed in water. Following an 8-wk period of dry storage at 4 C, conditioning yielded nearly 80% emergence for both collection timings, while emergence of seeds imbibed in water was 10% and 27% for early and late collections, respectively. Soil stratification in moist soil for 8 wk at 4 C was the second most effective treatment, yielding 46% to 49% emergence across both collections. Parameters of the Weibull function further indicated the conditioning treatment had the fastest rate of emergence and shortest lag phase between planting and first emergence. Methods to germinate A. trifida without an afterripening period have previously been unsuccessful. Therefore, the seed-conditioning method outlined in this work will be useful in expediting the confirmation of herbicide-resistant A. trifida incidences.

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.

Bromacil was introduced at the beginning of the 1960s for PRE and early POST control of grasses and broadleaf weeds, particularly in citrus (Rutaceae spp.) orchards and pineapple [Ananas comosus (L.) Merr.] plantations as well as in noncultivated areas. Both the acidic form of bromacil and its lithium salt are highly soluble in water; the herbicide is moderately to highly persistent in the soil with a half-life from 60 d to 8 mo and is prone to percolate in the soil and reach groundwater. In Costa Rica, bromacil was registered for both citrus and pineapple, but in recent years its major use has been in pineapple. An average of 60,000 kg of active bromacil per year were imported before its banning in 2017. Pineapple is grown in more than 40,000 ha; the recommended rate of bromacil was 1.6 to 3.2 kg ha−1. In a survey conducted by the National University between 2001 and 2004, bromacil was the most frequently found pesticide, at levels between 0.5 and 20 µg L−1, in water springs and wells in the pineapple-growing area of the Caribbean side of Costa Rica. Further studies conducted more recently also documented the presence of bromacil in the ground and surface water in areas where pineapple is planted. The local standard for the quality of drinking water of 2015 established maximum acceptable values of 0.1 µg L−1 and 0.5 µg L−1 for a single pesticide and for the sum of all pesticides present, respectively, but it was amended for bromacil to comply with requirements determined by the Constitutional Court to “non-detectable by method.” This paper provides an account of the scientific and administrative considerations for the banning of bromacil that occurred on May 24, 2017.

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.

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.

Madrone (Arbutus menziesii Purch.) and tanoak (Lithocarpus densiflora (H & A) Rehd.) are often considered undesirable along the Pacific Coast. These weed trees are removed to increase forage production; to remove competitors of more valuable timber trees, especially Douglas fir (Pseudotsuga menziesii (Mirb) Franco); or to obtain firewood or charcoal. Tanoak is occasionally cut for tanbark harvest. Control of stump sprouting following cutting would be desirable.

The most economical time to control invading noxious shrubs is at an early stage in the invasion, when stands are sparse. One method of doing this is with a ground spray rig (Fig. 1). With such a rig the problem is to get the guns out from the vehicle so that a reasonable-sized swath can be covered. The out-rigger apparatus described herein can be used to cover a swath of 50 feet where the brush is fairly dense, to 90 feet on sparser stands.

Several ring-substituted derivatives of benzoic acid inhibited pantothenate biosynthesis in Escherichia coli. The metabolic site of inhibition was the conversion of ketopantoate to pantoate. This action caused pantothenate-reversible reductions in growth only in strains of E. coli with inherent limited capacities for biosynthesis of ketopantoate. Inhibition of pantothenate biosynthesis was tentatively concluded to be of little physiological significance as a site of action responsible for herbicidal activities of benzoic acids.

Mature yellow foxtail [Setaria glauca (L.) Beauv.] infestations, growing in rows of corn, were harvested in 3 foot segments from paired 30 foot rows of corn. Basic analyses of variance were calculated so that the variances of plot sizes involving multiples of 3 feet could be determined and compared. Precision indices were calculated for harvesting various fractions of the plot area. Loss of precision did not exceed 25 percent when only 40 percent of the total area was harvested in random samples of 1-row X 3 feet, or in multiples of this basic unit. Practical implications of the findings are related to estimates of weed yields in crop-weed ecology studies and herbicide evaluation tests.

Weeds have plagued man in his agricultural pursuits since biblical times in spite of backbreaking efforts to control them by hand and mechanical methods. At this second meeting of the Weeds Journal of Weed Society of America it appears appropriate to review briefly some of the modern accomplishments in weed control and to take stock of future needs.

According to Bonner, at least three different oxidase systems may be involved in the final step of the transfer of electrons to oxygen. Each of the terminal oxidases has been shown to occur in many plants and in many relative combinations.

Studies with plant growth-regulators are severely handicapped unless methods are available for quantitative determinations of these chemicals. Beginning with the classical work of Went, several techniques have been developed to obtain a quantitative measure of plant growth-regulating chemicals. Brown and Weintraub, Hitchcock and Zimmerman and Frankton have discussed the use of biological assays as quantitative tests for various hormone-type chemicals. Thus far, the only biological methods developed beyond the semi-quantitative stage are those depending on cell elongation in shoots, inhibition or elongation of roots, and the stimulation of ovary development.

Stands of Russian knapweed (Centaurea repens L.) were reduced over 80 per cent by several combinations of crops, cultivation and herbicides. Two of the best crop rotations in a 4-year trial were: (1) a short season of intensive cultivation and a mid-August seeding of bromegrass that was sprayed with 1 lb/A of butoxyethanol ester of 2,4-dichlorophenoxyacetic acid (2,4-D) during June and 1 or 1½ lb/A during August of the second and third years. (2) Bromegrass seeded with an oat companion crop sprayed with ⅓ lb/A of 2,4-D ester the first year and annual applications of 2,4-D in June and mid-August during the second and third years. The best use of non-selective herbicides in two 2-year trials was spring application of 4 lb/A of diethylamine salt of 2,3,6-trichlorobenzoic acid (2,3,6-TBA) or 6 lb/A of diethylamine salt of polychlorobenzoic acid (PBA), plowing 10 days later, and a corn crop sprayed with ⅓ lb/A of 2,4-D ester followed by a spring-seeded oat crop sprayed with d13 lb/A of 2,4-D ester and postharvest application of 4 to 6 lb/A of 2,3,6-TBA and 6 to 8 lb/A of PBA, and plowing 10 days later. Reinfestation from established plants was not prevented, but annual application of 2,4-D prevented reinfestation from seedlings.

Growth of Oxalis cernua Thunb. was determined in different temperature regimes. Growth occurred in the 55 to 75 F range. Temperature variation promoted growth. Bulbs sprouted more rapidly and uniformly after storage at 35 F than after storage at 95 F. The weed probably is best adapted to areas with winter soil temperatures between 55 and 75 F.

Disking, relisting, cultivation and no repreparation were employed in repreparing for planting seedbeds that had received preemergence treatment with 3-(3,4-dichlorophenyl)1,1-dimethylurea (diuron). Only the relisting method of seedbed repreparation appeared hazardous with respect to crop injury from herbicidal residues. Retreatment with diuron tended to increase injury symptoms in replanted cotton but yields were not significantly reduced by retreatment. Early-season weed competition, preventable by preemergence treatment, appeared to be more hazardous to yields than slight to moderate herbicidal injury to the cotton. Cotton replanted on plots treated once or treated twice significantly outyielded that on untreated plots in one of the two years in which all plots were replanted.

Among 15 different herbicides tested for eradication of Turkey oak (Quercus laevis Walt.) over a period of four years on Lakeland fine sand in Florida, only monuron, diuron, and fenuron at minimal rates of 10 lb/A were effective. One full growing season after application was required for complete kill. Phenoxy compounds gave variable top-kill but not satisfactory control. AMS, dalapon, and four formulations of benzoic acid were ineffective in these tests.

Out of 13 different grasses, Pensacola bahiagrass (Paspalum notatum Flugge) and weeping lovegrass (Eragrostis curvula Schrad.) were best adapted to these deep sandy soils. Seedbed preparation was essential to obtain a good stand of either. After establishment, the lovegrass vigorously persisted throughout the experiment; the bahia also persisted but the lack of fertilization was extremely evident. Both grasses could be established satisfactorily on soil treated two years earlier with monuron or diuron at 10 lb/A.