Yaupon (Ilex vomitoria Ait. ♯ ILEVO) in the Post Oak Savannah of Texas was treated with liquid and dry formulations of herbicides. Sprays of Bay Met 1486 {N-[5-(ethylsulfonyl)-1,3,4-thiadiazol-2-yl]-N, N′-dimethylurea} and picloram (4-amino-3,5,6-trichloropicolinic acid), sprays and pellets of tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and boluses of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1N,3H)-dione] at 4.5 kg ae or ai/ha were the most effective treatments, reducing the canopy 87 to 99% and killing 68 to 93% of the yaupon after 2 yr. The percentage of dead yaupon after 1 yr was similar to that found 2 or 3 yr after treatment. Most herbicides, except clopyralid (3,6-dichloro-2-pyridinecarboxylic acid), reduced the yaupon canopy sufficiently to allow an increase in understory grass and broadleaf vegetation, particularly 1 yr after treatment.

The herbicide dichlobenil (2,6-dichlorobenzonitrile) inhibited soil nitrification significantly at 100 ppm following 1 and 2 weeks incubation but did not inhibit nitrification at the rates recommended for weed control.

Translocation of the 14C-labeled methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] was determined in cotton (Gossypium hirsutum L. ‘DPL 16′) from preemergence treatments and applications to leaves and stems in the field. Significantly greater methazole concentrations occurred in cotton from treatments to stems of 18 to 22-cm tall cotton than to leaves of 10 to 12-cm tall cotton or when applied preemergence. The radiolabel translocated primarily into the mature stems and leaves with lesser amounts translocating into the roots. Little 14C moved into the young growing points or into the seed and fiber of mature cotton. The distribution pattern of the 14C-label is characteristic of compounds which move primarily in the apoplast.

The historic maternal environment; the identity of competing, neighboring plants; and biotic stresses, such as fungal disease and herbivory, interact to influence the competitive ability, reproductive output, and plasticity of weed populations. A weed capable of altering its phenotype in response to environmental factors is better able to compete for resources in agroecosystems, thereby reducing crop yields and contributing more seeds to the seed bank. Velvetleaf is a highly competitive annual weed in many North American cropping systems, exhibiting a high degree of phenotypic plasticity in response to biotic and abiotic factors. We examined the effects of seed size (small and large), competitive environment (with and without soybean), and stress level (none = no treatment, moderate = pathogen inoculation, high = pathogen plus herbicide) on velvetleaf allometry and reproductive output during three field seasons. Only under the high-stress treatment was velvetleaf biomass, height, and reproductive output compromised (> 15% each), and these traits were further reduced with soybean competition. Soybean competition alone reduced velvetleaf biomass (> 50%), height (25%), and seed output (50%), but effects of competition varied with stress level. Velvetleaf plants that originated from large seeds (≥ 10 mg) generally outperformed plants originating from small seeds (< 10 mg) except under the high-stress treatment. These findings suggest that velvetleaf life-history traits and reproductive output in the current generation are a function of both present and historic factors. Management strategies for this species should involve tactics that not only reduce its competitive ability (e.g., biomass, height) but also decrease its seed production via synergistic stressors such as increased crop competitiveness, reduced-rate herbicide applications, and pathogen infection.

Cowvine (Ipomoea lonchophylla J.M. Black) is a native and widely spread summer broadleaf weed in Australia. It contains glycoresins, which are toxic to livestock. However, limited information is available on seed germination ecology and growth phenology of this species. A series of experiments were conducted to determine the response of I. lonchophylla to different environmental conditions. Results showed that the primary dormancy exhibited by I. lonchophylla is due to the physical impediment of the hard seed coat. The seed germination percentage was the highest at the constant temperature of 27 C and alternating temperatures of 35/25 C. Germination of I. lonchophylla was not stimulated by light, suggesting that this species is non-photoblastic. Ipomoea lonchophylla germination was intolerant of a medium to high level of salt stress, and germination was completely inhibited at 250 mM NaCl. The emergence of I. lonchophylla was not restricted by seeding depth up to 8 cm, but only 5% emergence was recorded when seeds were planted at a 16-cm depth. The germination percentage was also drastically reduced by 90% to 100% after exposure to either 3 mo in silage, 48-h digestion in steers, or silage plus digestion treatments. The growth and reproductive phenology of I. lonchophylla was affected by emergence time. Plants that emerged in late spring (November 15) were able to produce more berries per plant than those that emerged in midsummer (January 15) in southern New South Wales. Information gained in our study concerning high soil salinity, ensiling, and digestion will help to develop more sustainable and effective integrated weed management strategies for controlling and reducing the spread of this weed.

The effects of temperature and the annual growth cycle on the formation of root suckers were determined by propagating root cuttings of black locust (Robinia pseudoacacia L.). The percentage of cuttings which formed suckers in an air temperature of 60 F was significantly lower than that of cuttings at 70 to 80 F. In the annual growth cycle experiment, cuttings removed in June formed significantly fewer suckers than those removed during January, March, August, or November.

The pre- and postemergence herbicidal activities and specifications of 16 substituted toluidines on eight species were determined at two application rates. CF3-analogs were more active as preemergence treatments, and CH3-analogs were more active as postemergence treatments. Preemergence toxicity to crops was decreased in the CF3 and CH3 series when the N-substituents contained more than six carbons.

The injurious effects of different rates of fenuron (3-peynyl-1,1-dimethylurea) on four species of brush were recorded for two years in two different types of southwestern brushlands, the Oak-chaparral and the Chihuahuan Desert Shrub. Fenuron was more injurious to fire sprouts than to mature plants of turbinella oak (Quercus turbinella Greene) in the Oak- chaparral type especially at 2 to 8 lb/A ai. The effects of fenuron on mature plants were reduced by burning, suggesting that much of the fenuron absorbed was residual in the stems, twigs, and leaves where it was destroyed by the fire. The effect of fenuron on the fire sprouts changed only slightly between six months and two years. Gibberellic acid was applied to sprouts and mature oak plants appeared to slightly reduce the injurious effects of some rates of fenuron during the first six months but no gibberellin induced differences were observed after two years. In the Chihuahuan Desert shrub type, tarbush (Flourencia cernua DC.) and whitethorn (Acacia constricta Benth.) were about equally susceptible to injury by fenuron with creosotebush (Larrea tridentata (DC.) Cov.) slightly more resistant. Summer applications just before the rainy season were most effective and 4 lb/A combined high shrub kill with greatest grass growth.

Although 8 and 16 lb/A ai killed and injured both grasses and shrubs on the oak plots, grass naturally reseeded into these plots within six months after treatment, but on the Chihuahuan Desert area grass had not recovered on the plots treated at 8 lb/A after two years. This difference in grass re-establishment was probably due to rainfall differences which would give differences in leaching of fenuron. Palatability of the grasses in the oak plots increased due to fenuron treatments, particularly on the heavily treated plots. These studies indicate that moderate rates of fenuron, applied just prior to favorable seasonal rains and repeated at several-year intervals, may be used to control turbinella oak sprouts and mature Chihuahuan Desert shrubs. However, treatments would only be economical where high forage and watershed values would result.

Dalmatian toadflax (Linaria dalmatica (L.) Mill.), a native of southeast Europe, has acquired a firm position in some plant communities in northeastern Washington. The first herbarium specimen for Washington State University was collected in 1926 on the Little Spokane River near the city of Spokane. Since that time, it has invaded a considerable area of northeastern Washington, and scattered patches appear over much of the eastern half of the State. In 1954 the estimated acreage was 30,000. Dalmatian toadflax has now spread into Idaho, western Montana, and Oregon. It also occurs in the prairie provinces and inter-mountain regions of Canada and has been reported near Flagstaff, Arizona.

In reviewing weed control literature, papers are frequently encountered in which the data have been presented without statistical evaluation. It is important for research workers in the herbicide field to be able to estimate the validity of their comparison just as it is for the workers engaged in fertilizer studies or any other phase of field research. Arithmetic means presented alone in a graph or in a table are extremely difficult to evaluate. Even though the author of a paper may have confidence in the significance of his data, it is difficult for the reader of a research report to evaluate the conclusions if an estimate of the experimental error is not presented. This may seem to place undue emphasis on statistical analysis itself. Yet in the relatively new field of weed control, few workers have had sufficient experience to judge the significance of differences of varying degree.

Injections with 4-amino-3,5,6-trichloropicolinic acid (picloram), 2-methoxy-3,6-dichlorobenzoic acid (dicamba), and butoxyethanol ester of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) satisfactorily killed the tops of scarlet oak (Quercus coccinea L.) and white oak (Quercus alba L.) when applied in March or June. Triethylamine salt of 2,4,5-T adequately killed the tops of the oaks in June but not in March. Picloram was the most lethal herbicide used on red maple (Acer rubrum L.), and sprouting was controlled more effectively on all species with picloram than with the other herbicides.

The principle of the variable dosage or logarithmic sprayer was described first in 1955. Since that time at least two sprayers utilizing this principle have appeared. Certain limitations were, however, encountered in adapting these sprayers for small plot testing under field conditions.

The effect of ethametsulfuron on populations of canola was evaluated in field and laboratory trials. Three canola populations (TR4, CB9604, and BC86-18) and the open-pollinated canola cv. ‘AC Parkland’ were treated with several doses of ethametsulfuron at the two- to four-leaf stage. In the field experiment, plant densities were determined before spraying and again at plant maturity. Density reductions during the growing season were observed for all populations (6 to 17%), but reductions due to ethametsulfuron above 0.3 g ha−1 depended on year, being noted for TR4 in 1997 (40 to 65%) only. In laboratory trials, only TR4 demonstrated sensitivity to ethametsulfuron, up to 49% visual damage averaged over all plants. The response was binary, with about 40% of plants at any given herbicide rate surviving unharmed and the remaining 60% of plants exhibiting > 90% visual damage. It is concluded that TR4 is sensitive to ethametsulfuron and further work, including a comprehensive genetic study, is required to determine the inheritance of sensitivity.

The extent to which weed species vary in their ability to acquire and use different forms of nitrogen (N) (inorganic and organic) has not been investigated but could have important implications for weed survival and weed–crop competition in agroecosystems. We conducted a controlled environment experiment using stable isotopes to determine the uptake and partitioning of organic and inorganic N (amino acids, ammonium, and nitrate) by seven common weed and non-weed species. All species took up inorganic and organic N, including as intact amino acids. Concentrations of 15N derived from both ammonium and amino acids in shoot tissues were higher in large crabgrass [Digitaria sanguinalis (L.) Scop.] and barnyardgrass [Echinochloa crus-galli (L.) P. Beauv] than in common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and sorghum-sudangrass [Sorghum bicolor (L.) Moench × Sorghum bicolor (L.) ssp. drummondii (Nees ex Steud.) de Wet & Harlan]. In contrast, the concentration of 15N derived from nitrate was higher in wild mustard (Sinapis arvensis L.) shoots than in wild oat (Avena fatua L.) shoots. Root concentration of 15N derived from ammonium was lower in sorghum-sudangrass compared with other species, except for A. retroflexus and A. fatua, while root concentration of 15N derived from nitrate was lower in A. retroflexus compared with other species, except for C. album and S. arvensis. Discriminant analysis classified species based on their uptake and partitioning of all three labeled N forms. These results suggest that common agricultural weeds can access and use organic N and differentially take up inorganic N forms. Additional research is needed to determine whether species-specific differences in organic and inorganic N uptake influence the intensity of competition for soil N.

Control of weeds growing around field edges to limit seed production is an important component of preventative weed management. POST herbicide rates that are effective on weeds growing within a dense corn or soybean canopy may not be high enough to control weeds at the edge of a field. A study was conducted from 2004 through 2006 to compare velvetleaf growth and fecundity at the edge of the field as opposed to within the crop in response to a range of glyphosate rates. Treatments included position (plot center or edge), time of emergence (VE or V4 crop growth stage) and glyphosate rate (0 to 900 g ae ha−1). Without herbicide application, velvetleaf plants grown on the edge flowered earlier, had thicker stems, and produced more seed capsules than plants grown in the center of the plots. At glyphosate application rates of 200 to 900 g ha−1, the percentage of plants surviving and reproducing was higher on the edge than within the crop. Edge plants treated with 900 g ha−1 of glyphosate produced more seeds than center plants that received no herbicide. Dose–response curves were used to estimate the glyphosate rate that would reduce seed production of surviving plants to 80% of the untreated plants. Plants emerging at the VE stage were estimated to require 300 g ha−1 within the corn or soybean canopy and 668 g ha−1 on the crop edge, whereas plants emerging at the V4 stage would require 0 g ha−1 within the canopy and 280 g ha−1 on the crop edge.

Fenac [(2,3,6-trichlorophenyl)acetic acid] and 4-amino-3,5,6-trichloropicolinic acid (picloram) at 28 and 2.2 kg/ha, respectively, controlled woollyleaf bursage (Franseria tomentosa Gray) for 3 years in noncropped areas. Effective control of woollyleaf bursage was obtained when treated at the bud stage or earlier with an ester formulation of (2,4-di= chlorophenoxy)acetic acid (2,4-D) at 2.2 kg/ha or 3-amino-s-triazole (amitrole) at 4.5 kg/ha in an oil-water emulsion carrier or 3,6-dichloro-o-anisic acid (dicamba) at 2.2 kg/ha in a water carrier with 0.5% surfactant. Picloram, at 0.44 kg/ha or more, controlled woollyleaf bursage at any time of application.

Dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) applied at 0.37 kg/ha controlled black nightshade (Solanum nigrum L.) better than did trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0.56 kg/ha. Dinitramine applied at 0.37 kg/ha was equal to 0.56 kg/ha of trifluralin for control of green foxtail [Setaria viridis (L.) Beauv.], yellow foxtail [Setaria glauca (L.) Beauv.], and redroot pigweed (Amaranthus retroflexus L.). Dinitramine produced more root aberrations in sugarbeets (Beta vulgaris L. ‘Mono Hy D2′) than did trifluralin when sprayed on nonexposed or exposed hypotcotyledonary tissues of seedlings. When soil surrounded most of the hypocotyls at the time of application, 0.56 kg/ha of dinitramine affected 57 to 87% of the roots, whereas the same rate of trifluralin affected 1 to 8% of the roots. When the hypocotyls were exposed at the time of application, 100% of the roots were affected by dinitramine compared to 25% of all roots treated with trifluralin. Dinitramine applied at 0.37, 0.42, and 0.56 kg/ha lowered the quality and yield of sugarbeet roots, with the highest rate significantly reducing percentage purity, percentage sucrose, and recoverable sucrose. Trifluralin did not affect these parameters.

Regional pine seedling tolerance experiments were conducted on five pine (Pinus spp.) species at ten forest nurseries in 1974. Similar studies in 1975 included four pine species at nine locations. From these studies, herbicides appearing safe for preemergence use are bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate] at 1.7, 3.4, and 6.7 kg/ha; butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] at 2.2, 3.4, 4.5, and 6.7 kg/ha, napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] at 1.7 kg/ha; napropamide at 1.1 kg/ha plus bifenox at 3.4 kg/ha; dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) at 0.37 and 0.74 kg/ha; diphenamid (N,N-dimethyl-2,2-diphenylacetamide) at 4.5 kg/ha, trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 1.1 kg/ha; and profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] at 1.1 and 2.2 kg/ha. Southern pine seedling tolerance to oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) was unacceptable at 1.1 and 2.2 kg/ha. Napropamide severely stunted seedlings at 6.7 kg/ha but affected seedlings only slightly at 3.4 kg/ha.

The effect of picloram (4-amino-3,5,6-trichloropicolinic acid) on regeneration of detached leaves of Echeveria elegans Bgr. was studied. Picloram stimulated callus production at all concentrations. Low concentrations of 1 to 15 ppmw picloram did not affect shoot organogenesis and the same, however, stimulated rhizogenesis. Inhibition of both root- and shoot-organogenesis was noticeable at concentrations below 20 ppmw and above. Roots increased in number at all picloram concentrations below 40 ppmw, the maximum number being at concentration of 15 to 20 ppmw of the herbicide. Observations indicated that root elongation was considerably suppressed. Picloram-induced callus contained mature parenchyma cells devoid of contents and considerable amount of tissue disruption was noticed. Irregular vascular differentiation and obliteration of tissues particularly in the region of tracheary elements, were obvious. Although normal apical organization was lacking in root primordia and in arrested short roots, these elongated normally into mature roots when they were transferred to water, thus indicating that apical meristems were not severely affected by picloram.