Basal bark treatment with triclopyr butoxyethyl ester is used to control woody invasive plants, including Brazilian peppertree (Schinus terebinthifolia Raddi). However, the ester formulation cannot be applied where standing water is present, which includes wetlands where S. terebinthifolia is found. In 2009, a low-volatile acid formulation of triclopyr was labeled for use in aquatic sites, which allows for basal bark applications when standing water is present. This formulation may have utility for controlling woody plants in standing water. However, anecdotal observations of injury to non-target plants following applications during periods of inundation have been reported. To address this, mesocosm studies were conducted to assess non-target injury through triclopyr root exudation or release from the surface of treated stems via flooding. Mesocosms contained S. terebinthifolia as the treated target, while sugarberry (Celtis laevigata Willd.), buttonbush (Cephalanthus occidentalis L.), and red maple (Acer rubrum L.) were included as non-targets. In the first study, the pathway of root exudation for non-target injury following triclopyr (34 g L−1) basal bark application was isolated with activated charcoal placed at the soil surface. In the second study, mesocosms were flooded to assess triclopyr release from the surface of treated stems and subsequent non-target injury. Defoliation of non-target species posttreatment was ≤8%, and triclopyr was detected at ≤5 µg L−1 in mesocosm wells when activated charcoal was present. Posttreatment non-target defoliation up to 92%, coupled with triclopyr concentrations in surface waters and wells as high as 4,637 µg L−1, indicated triclopyr movement as a result of flooding. Additionally, triclopyr non-target injury from soil activity independent of flooding was observed. These findings provide limited evidence of triclopyr root exudation but considerable evidence of triclopyr release during flooding following basal bark treatment and support a cautionary approach to basal bark application when standing water is present.

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.

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.

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.

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 control as we know it today is a new field with frontiers and relationships that have not been clearly charted. Weed control workers are, in a sense, pioneers. The background of knowledge is still not great and many of the questions our farmers are asking have no unequivocal answer. The sources of information are still not clearly defined and many agencies are involved in the search for information. Within any one university or college one frequently finds information that the weed specialist needs developing in the departments of botany, agronomy, vegetable crops, horticulture, chemistry and agricultural engineering. Commercial organizations of many kinds are discovering new facts that we need to know. And not the least of these sources of information is the Extension Service itself because county men, and the farmers they work with, are constantly adding to our knowledge. It is a dull man indeed who can view field after field treated to control weeds without arriving at a good working hypothesis of what can be done and how to go about doing it. The role of the Extension Service in the development of weed control over the past ten years has been overlooked in our emphasis on research. I would not for a moment minimize the importance of the emphasis on research but I do decry the lack of parallel emphasis on encouraging the use of the knowledge so developed. And the Extension Service in the many states has been a potent force in developing the new information credited to research.

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.

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.

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.

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.

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.

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.

The phytotoxicity of postemergence propanil (3′,4′-dichloropropionanilide) to hard red spring (HRS) wheat (Triticum aestivum L.) was determined in the field and controlled environmental chamber. HRS wheat tolerance to propanil was influenced by cultivar, crop growth stage at time of application, and posttreatment temperature. Injury to wheat from propanil was greater at the five- than two-leaf stage of application and at 30- than at 10- or 20-C posttreatment temperatures. ‘Butte’ wheat was the most susceptible HRS wheat cultivar to propanil, with yield reductions ranging from 15 to 40% depending upon year and crop growth stage at application.

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.

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.

About 25 ppm of 4-amino-3,5,6-trichloropicolinic acid (picloram) usually were detected on grass, primarily buffalograss (Buchloe dactyloides (Nutt.) Engelm.) and blue grama (Bouteloua gracilis Willd. ex HBK Lag ex Griffiths), immediately after application of 0.28 kg/ha picloram + 0.28 kg/ha (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in northwest Texas. Less than 1 ppm of picloram usually was detected in grass tissue 30 to 60 days after treatment. At one location, detectable picloram increased in grass tissue from 32 to 60 days after application. Increases of picloram in aerial grass tissue were attributed to root uptake during a flush of vegetative growth. Picloram dissipation from grasses was not affected by irrigation to runoff at 10, 20, or 30 days after application. Detectable picloram was reduced by 93% in herbaceous, broadleaf species by 30 days after application. Treated sand shinnery oak (Quercus havardii Rydb.) leaves at the soil surface caused a slight increase of picloram in surface litter.

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.

The specific and general postemergence herbicidal properties of N′-4-(4-chlorophenoxy)phenyl-N,N-dimethylurea [chloroxuron] were influenced by formulation and the carrier employed.