Herbicide-resistant weeds are a growing concern globally; in response, new herbicide resistance traits are being inserted into crops. Isoxaflutole-resistant soybean [Glycine max (L.) Merr.] will provide a new mode of action for use in this crop. Ten experiments were conducted over a 2-yr period (2017, 2018) to determine herbicide interactions between isoxaflutole and metribuzin on soybean injury, weed control efficacy, and soybean yield on a range of soil types. Soybean leaf-bleaching injury caused by isoxaflutole was most severe at sites with higher levels of rainfall after application. Control of weed species with isoxaflutole (52.5, 79, and 105 g ai ha−1) and metribuzin (210, 315, and 420 g ai ha−1) differed by site based on amount of rainfall after application. At sites where there was sufficient rainfall for herbicide activation, isoxaflutole at all rates controlled common lambsquarters (Chenopodium album L.), Amaranthus spp., common ragweed (Ambrosia artemisiifolia L.), and velvetleaf (Abutilon theophrasti Medik.) >90%; metribuzin at all rates controlled Amaranthus spp. and witchgrass (Panicum capillare L.) >80%. Control of every weed species evaluated was reduced when there was limited rainfall after herbicide application. The co-application of isoxaflutole + metribuzin resulted in additive or synergistic interactions for the control of C. album, Amaranthus spp., A. artemisiifolia, A. theophrasti, Setaria spp., barnyardgrass [Echinochloa crus-galli (L.) P. Beauv], and P. capillare. Isoxaflutole and metribuzin can be an effective management strategy for common annual broadleaf and grass weeds in Ontario if timely rainfall events occur after herbicide application.

Winter wild oat [Avena sterilis ssp. ludoviciana (Durieu) Gillet & Magne; referred to as A. sterilis here] is one of the major weed species of the Avena genus, given its high competitive ability to infest cereal crops worldwide, with special concern in Spain. A nine-location field experiment was established across Spain where a total of 400 A. sterilis seeds per location were sowed in four replicates in autumn 2016 to monitor the emergence during two growing seasons in dryland conditions. The data were used to test the prediction ability of previously published thermal (TT) and hydrothermal time (HTT) models and to develop new models, if required. Overall, the average percentage of emergence was 30% during the first season and 21% during the second season. In both seasons, the main emergence flush occurred between November and February. According to the phenological stage, A. sterilis achieved the tillering earlier in southern sites, between November 25 and the end of December, compared with northern sites, where this stage was reached at the end of January. The newly developed model described the emergence with precision, using three cardinal temperatures to estimate the TT. The three cardinal points were established at −1.0, 5.8, and 18.0 C for base (Tb), optimum (To), and ceiling temperature (Tc), while the base water potential (Ψb) was established at −0.2 MPa for the HTT estimation. This study contributes to improving prediction of the emergence of A. sterilis and provides knowledge for decision support systems (DSS) for the control of this weed.

According to climate models, drier summers must be expected more frequently in Central Europe during the next decades, which may influence plant performance and competition in grassland. The overall source–sink relations in plants, especially allocation of solutes to above- and below-ground parts, may be affected by drought. To investigate solute export from a given leaf of broadleaf dock, a solution containing 57Co and 65Zn was introduced through a leaf flap. The export from this leaf was detected by analysing radionuclide contents in various plant parts. Less label was allocated to new leaves and more to roots under drought. The observed alterations of source–sink relations in broadleaf dock were reversible during a subsequent short period of rewatering. These findings suggest an increased resource allocation to roots under drought improving the functionality of the plants.

A microcoulometric gas chromatographic method with a sensitivity of 0.01 ppm is described for the analysis of 2,4-dichlorophenoxyacetic acid (2,4-D) in milk and forage. The method will analyze 2,4-D as the acid, ester, and bound form from a single sample. Results show the superiority of this method over previous procedures. The formation of 2,4-D ethyl ester from the butyl ester in forage is discussed.

In 1994, the National Jointed Goatgrass Research Program was initiated with funding from a special USDA grant. The 15-yr program provided $4.1 million to support jointed goatgrass (Aegilops cylindrica Host.) research and technology transfer projects in 10 western states. These projects resulted in approximately 80 refereed manuscripts, including journal articles and extension publications. The research covered various topics related to the biology and ecology of jointed goatgrass as well as its management and control in wheat (Triticum aestivum L.) production systems. This review summarizes the research on jointed goatgrass published after Donald and Ogg’s 1991 review, most of which was conducted as part of the USDA-funded National Jointed Goatgrass Research Program. Specific topics that were studied and reviewed here include A. cylindrica genetics, especially as it relates to gene flow and hybridization rates with wheat and fertility of the resulting hybrids; vernalization requirements; seed dormancy, longevity, and germination requirements; competitiveness with wheat; and herbicide resistance acquired through evolution or gene flow from wheat. With respect to management, a wide variety of practices were evaluated, including various tillage types and frequencies; crop rotations, especially diversified wheat production systems that include spring-seeded annual crops; competitive wheat cultivars, seeding dates, seeding density, and row spacing; fertility management, including nitrogen application timing and placement; and field burning. Finally, many studies evaluated the use of herbicides, especially the introduction of imazamox in imidazolinone-resistant wheat cultivars, as well as comparison of adjuvant systems and application timings. In addition to the many management practices that were studied individually, several integrated management systems were evaluated that combined crop rotations, tillage, and herbicide programs. Between 1993 and 2013, weed scientists in 14 western states estimated that jointed goatgrass infestations decreased by 45% to 55% and attributed the reduction to the implementation of more diverse crop rotations, improved cultural practices, and use of imazamox-resistant wheat technology. This is evidence that the practical implications of the National Jointed Goatgrass Research Program have been successfully implemented by growers throughout the western United States.

Field experiments were conducted to determine whether aerial and subterranean stem sections taken from Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] plants in four stages of development (spring-vegetative, bud, postbloom, and fall-vegetative) could survive and produce infestations the following year. Partially buried aerial stem sections from all stages of development had greater survival 28 days after planting than completely buried aerial stem sections. Few completely buried aerial stem sections survived. Partially or completely buried subterranean stem sections from Canada thistle at the postbloom stage had the highest survival rate. Few partially or completely buried subterranean stem sections from the other three growth stages survived. Surviving stem sections from spring-vegetative, bud, and postbloom stages of Canada thistle produced adventitious roots that overwintered and produced new infestations the following spring. Surviving stem sections from Canada thistle at the fall-vegetative stage did not develop an adequate root system for winter survival.

Since weeds in cranberry bogs cannot be successfully controlled by mechanical equipment, there has been considerable interest in chemical means of control. Among the chemicals that have been and are presently being used are iron sulfate, paradichlorobenzene, sodium chloride, sodium arsenate, sodium arsenite, copper sulfate, kerosene, and other herbicidal oils (2). All these chemicals have to be applied in relatively large quantities, which makes for a large per-acre cost of treatment and involves many problems inherent in the application of large quantities of materials. There is, then, considerable interest in a chemical which can be applied in relatively small quantities and which will provide satisfactory control of weeds in the bogs.

Winter wheat infested with four populations of coast fiddleneck (Amsinckia intermedia Fisch. & May) was treated with 2,4–dichlorophenoxyacetic acid (2,4–D). One weed per square foot reduced grain yield. Weeds competed strongly as early as the rosette stage. Treating the weed infested wheat with 2,4–D increased yield. A vigorous, early-established crop of wheat competed effectively with the weeds.

Certain members of the phenyl carbamate series and some salts of trichloroacetic acid have been known for several years to possess strong herbicidal properties, particularly toward monocotyledonous plants. This action has been described by Ivens and Blackman (4), McCall and Zahnley (5), Freed and Bierman (2), and others. Inconsistent results obtained in the usage of these chemicals have discouraged many workers from accepting them as useful weed control tools. Recently, Freed (3) analyzed several factors influencing the success or failure of IPC (isopropyl–n–phenyl carbamate). Among these are biochemical specificity, decomposition by soil microorganisms, moisture requirements, and stage of plant development. It has also been demonstrated by Anderson et al (1) that rapid evaporation of carbamates may be a critical factor at temperatures above 75 °F.

Autoradiographs following treatment of Cyperus esculentus L. with C14-labeled amitrole indicated that it was readily translocated from the point of application to the seed. Seed germination was significantly reduced following amitrole applications.

Thiobacillus thioparus, Azotobacter chroococcum, Rhizobium leguminosarum, Aspergillus niger, Paramecium caudatum, Colpidium sp., and a mixed culture of soil ciliates were not adversely influenced nor stimulated by the presence of dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA). Soil from plots treated 7 years at 5.0 ppm showed no accumulation of DCPA. Plate counts of actinomyces, bacteria, and molds from field and laboratory-treated soils showed no adverse effect. A mixed culture of soil algae and fungi grew significantly more in the presence of DCPA.

Oxalic acid and oxalates occur in many plants. Consumption of plants containing high concentration of oxalates can be poisonous to animals. This has been reported by several investigators (5, 7, 9). However, in only a few plants are oxalates found in sufficient quantities to be lethal. Some species with a relatively high oxalate content are: sorrel (Rumex spp.), rhubarb (Rheum spp.), greasewood (Sarcobatus vermiculatus Torr.), soursobs (Oxalis cernus Thunb.), and halogeton (Halogeton glomeratus C. A. Mey.).

Experiments conducted for two consecutive years indicated that barnyardgrass, large crabgrass, and giant foxtail interfered with the growth and development of container-grown ‘Gold Drop’ bush cinquefoil. Grass weed densities ranging from one to six weeds per container reduced Gold Drop bush cinquefoil growth. Bush cinquefoil shoot dry weight, averaged over all grass weeds, was decreased as much as 75% after 83 days of interference. The reduction of cinquefoil growth was independent of the number of grass weeds in the container.

A 3.6 g/L solution of glyphosate [N-(phosphonomethyl)glycine] applied to selected parts of bermudagrass [Cynodon dactylon (L.) Pers.] shoots did not kill the entire plant. However, phototoxicity increased as more parts of the plant were treated. No differences were observed when solutions of 3.6 and 5.4 g/L glyphosate were applied at 94 and 373 L/ha. However, greater herbicide efficacy was obtained when 1.8 g/L solution was applied at the higher volume. Translocation of this herbicide appeared to follow the typical source-sink relationship. A 7.2 g/L solution of glyphosate applied at 373 L/ha was necessary to kill the plant.

The phylogenetic relationships within two major locoweed genera, Astragalus and Oxytropis, and among varieties of woolly loco found in New Mexico were analyzed by comparing their chloroplast rpoC1 and rpoC2 gene sequences. Nucleic acids from locoweed species and varieties collected from different geographical locations in New Mexico were amplified using specific primer sets and subjected to restriction fragment analyses. Identity of the amplicons was confirmed by determining the 5′-end sequences from pea and woolly loco var. matthewsii. The amplified sequences from all samples were digested with 16 different restriction enzymes. Presence or absence of individual restriction fragments was scored as binary characters and used to develop a similarity coefficient matrix for cladistic analyses to determine the phylogenetic relationships. The target sequence was conserved, yielding 7% polymorphic data. Oxytropis species were monophyletic and, as expected, formed a clade distinct from Astragalus. The average similarity coefficient among woolly loco varieties was very high (0.9733), but the varieties still separated into three different clades. The phylogenetic relationship among woolly loco varieties coincided with their geographic distribution but was unrelated to insect feeding preference.

Annual weeds were allowed to compete until or after each of the first three postemergence irrigations of furrow-irrigated cotton (Gossypium hirsutum L. ‘Deltapine 16’). Beds and furrows were shaped with a sectioned, rolling cultivator three times between cotton emergence and the second irrigation. Cotton boll components and fiber properties were not affected by periods of competition with annual weeds. Weeds allowed to compete after the first or second irrigations significantly reduced the 4-year average yield of cotton by 16 and 12%, respectively. Competition that began after the third or fourth irrigation, or that ended after the first, second, or third irrigation was less detrimental and did not significantly affect yields.

Detection and degradation of linuron [3-(3,4-dichlorophenyl) -1 - methoxy -1 - methylurea] in organic soils were studied using biological assays and chromatographic techniques. The level of linuron that caused 50% growth reduction of onion (Allium cepa L.) varied among three soils of greatly differing organic matter contents. Linuron and its metabolites were successfully separated with florisil column chromatography using a five-fraction solvent system; however, only linuron and 3 - (3,4 - dichlorophenyl) -1 -methylurea could be extracted from organic soil samples at satisfactory recovery rates. Soil samples from eight grower fields and from field plots were analyzed to determine the residue level of these two compounds. Quantitative assessment of the compounds was made with high pressure liquid chromatography. Results of the biological assay and chromatographic analysis showed that linuron and its phytotoxic metabolite, 3 - (3,4 - dichlorophenyl) -1 - methylurea, were not accumulating in the organic soils of Ontario and that the levels detected were not phytotoxic to onions when grown in pot bioassays.

Effects of the herbicides SC-0224 and glyphosate on the pool levels of free amino acids, soluble protein, and protein synthesis in inflated duckweed were compared. SC-0224 caused larger increases than glyphosate in the pool levels of amino acids; the increases caused by SC-0224 were similar, however, to those caused by trimethylsulfonium iodide (TMS-I). Expressed on a per gram fresh weight basis, none of the treatments changed soluble protein or the incorporation of 14C-leucine into soluble protein. On a per flask basis (allowing for decreased growth in treated flasks), both herbicides and TMS-I decreased soluble protein and 14C-leucine incorporation. Decreases in soluble protein and 14C-leucine incorporation were equal for SC-0224 and TMS-I but larger than for glyphosate. These data indicate that differences in the phytotoxicity of SC-0224 and glyphosate may be due to the action of the trimethylsulfonium portion of the SC-0224 structure.

The persistence and effectiveness in pumpkin [Cucurbita moschata (Puch.) Poir.] weed control of several starch xanthide (SX) and commercial formulations of the ammonium (NH3) salt and methyl (CH3) ester of chloramben (3-amino-2,5-dichlorobenzoic acid) were studied in the laboratory and field. The soluble concentrate (SC) of chloramben NH3 salt and the emulsifiable concentrate (EC) of chloramben CH3 ester controlled weeds throughout the growing season on a silt loam soil. SC chloramben NH3 salt was not effective, and EC chloramben CH3 ester was inconsistent in weed control on sandy soil. Manipulation of the SX formulation produced products with slow, uniform release rates. The release rates (crosslinking reagent in parenthesis) rank as follows, from fastest to slowest: SX(Ca2+) CH3 ester = SX(H2O2) acid > SX(H2O2) CH3 ester > SX(Fe3+) acid > SX(Fe3+) CH3 ester. In trials on silt loam and sand, SX formulations did not control weeds better than EC chloramben CH3 ester.

Laboratory studies were conducted to determine the effect of seed coat on woolly cupgrass seed moisture and oxygen uptake, and to determine if water-soluble growth inhibitors are present in the seed. Intact dormant seeds did not respond to any temperature regime or to oxygen concentrations above atmospheric level. Dehulling increased germination of dormant seed to about 85%. Oxygen concentrations above atmospheric level increased germination of partially dehulled (1/4 distal end of the seed dehulled) seeds an additional 10%. Oxygen uptake by dehulled dormant and intact nondormant seeds was greater than intact dormant seeds. Leaching intact dormant seeds did not promote germination, nor did the leachate inhibit germination of nondormant seeds. Embryos excised from dormant seeds germinated under laboratory conditions. Results from this study suggest that the woolly cupgrass seed coat may inhibit germination by controlling oxygen availability to the embryo.