Showy crotalaria (Crotalaria spectabilis Roth) seed dormancy was due to seed coat impermeability to water. The seed coats became impermeable during later stages of maturation on the plant. When incubated immediately after harvest, 9% of the mature, black seeds (11% water content) imbibed water and germinated. The remaining 91% had impermeable coats and did not germinate. After dry storage for 3 months at 23 C, 24% of the seeds imbibed water and germinated. Seeds of another seed lot, which contained seeds of different maturity stages, attained 47% imbibition and germination after storage for 1 yr. The dry, less mature green seeds had a higher percentage (51%) of permeable seeds than did the black seeds (31%) from the same lot. Several seed coat treatments induced imbibition of water and germination of previously impermeable seeds. Effective treatments included piercing of seed coats, scarification with sandpaper, soaking in 70 C water, and simply applying pressure on the strophiole area. Covering the pressed strophiole with petroleum jelly significantly blocked imbibition and indicated that water entered the seeds at only the pressed area. However, studies indicated natural loss of impermeability in showy crotalaria seeds may occur at other sites as well.

Smutgrass [Sporobolus poiretii (R. & S.) Hitchc.] in native grass and ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] pastures near Caldwell, Texas, was sprayed with herbicides in 1975 and 1976. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 4.5 kg/ha; dalapon (2,2-dichloropropionic acid) at 5.6 kg/ha; glyphosate [N-(phosphonomethyl)glycine] at 0.6 and 2.2 kg/ha; and bromacil (5-bromo-3-sec-butyl-6-methyluracil), tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] at 1.1 and 2.2 kg/ha reduced smutgrass foliar cover, particularly if applied from July to November. Dalapon, tebuthiuron, and hexazinone were the most effective herbicides for reducing smutgrass foliar cover. Other grasses generally replaced smutgrass controlled with hexazinone or tebuthiuron, while broadleaf species mostly replaced smutgrass in plots controlled with dalapon or glyphosate. Dalapon, glyphosate, bromacil, hexazinone, and tebuthiuron caused some injury to Coastal bermudagrass for 3 or 4 months following treatment. By fall of the year after treatment Coastal bermudagrass cover in treated plots was equal to or greater than that in untreated plots.

Annual bluegrass (Poa annua L.) growing in bermudagrass completes its life cycle in May and dies leaving open spaces in the turfgrass. This occurs at a time when summer annual weeds are germinating and these weeds fill the space formerly occupied by the annual bluegrass. As the summer annual weeds die in the fall, annual bluegrass germinates and fills the space formerly occupied by the summer annual weeds. To control annual bluegrass, it is important to control the summer annual grasses and manage the bermudagrass [Cynodon dactylon (L.) Pers.] to maintain a competitive groundcover especially during the peak germination period for the weeds. Herbicide programs over a three-year period were designed to control annual grasses with treatments in April for large crabgrass [Digitaria sanguinalis (L.) Scop.], in May or June for goosegrass [Eleusine indica (L.) Gaertn.] and in late August for annual bluegrass. Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-ozadiazolin-5-one] applied in August gave complete control of annual bluegrass. Although oxadiazon has a long residual life in the soil, annual bluegrass was poorly controlled with treatments made in June. Fall (August or September) applications of benefin [N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine], prosulfalin N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine and butralin [4-(1,1-dimethylethyl-N-(1-methylpropyl)-2,6-dinitrobenzenamine] provided adequate control of annual bluegrass with only a few exceptions during the three-year period. Bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] gave variable control of annual bluegrass; however, this was improved in programs with oxadiazon which provide goosegrass control during summer. In these studies, DCPA [dimethyl tetrachloroterephthalate], even with three applications a year, gave very little control of annual bluegrass. When oxadiazon was used in rotation with DCPA, adequate control was obtained.

Roots or shoots of oats (Avena sativa L. ‘Dal’) and peas (Pisum sativum L. ‘Early Perfection’) were exposed to vapors of 14C-labeled benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin [N-(2-chloroethyl)-2,6 dinitro-N-propyl-4-(trifluoromethyl)aniline], oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). All of the dinitroaniline herbicides except oryzalin were absorbed by roots and shoots of germinating oats and peas. Some root-shoot translocation of the herbicides was observed in peas, but no shoot-root transport could be detected in either peas or oats. In peas, 14C from root-absorbed benefin, fluchloralin, profluralin and trifluralin was detected in shoots, and 14C from benefin and trifluralin was detected in cotyledons. In general, vapor absorption was correlated with rates of herbicide volatilization.

Redroot pigweed (Amaranthus retroflexus L.) and robust foxtail [Setaria viridis (L.) Beauv. var. robusta-alba Schreiber or Setaria viridis var. robusta-purpurea Schreiber] were investigated to measure the accumulation of nonstructural carbohydrates throughout two separate growing seasons. Pigweed tended to accumulate more total nonstructural carbohydrates (TNC) than foxtail, particularly in the roots. In both weeds, peak levels of TNC in leaves, stems, and roots occurred during early flowering. The primary nonstructural carbohydrate in the leaves of both weeds was starch. Reducing sugars were the predominant nonstructural carbohydrate in the stems. Starch accumulated more in the leaves of the upper third of the plant and reducing sugars occurred in the greatest quantity in the middle strata of the stem. Accumulation levels of TNC in the plant organs suggested that the stem was a major sink during the vegetative growth phases of both pigweed and foxtail.

Dwarf spikerush [Eleocharis coloradoensis (Britt.) Gilly] is an aquatic plant that will displace waterweeds. It was studied to obtain information that will help to manage unwanted vegetation in natural aquatic situations. The morphology of seed and tubers was examined at the light- and scanning-electron microscope levels. Inflorescences were found to bear 3 to 12 florets that matured acropetally. The pericarp was made up largely of rows of annulated cells covered with a water-soluble, waxlike substance that leached away when stored in water at 4 to 6 C. The seed coat consisted of three layers. Each layer contained lipids, giving evidence that they were composed of cutin. When the seed germinated, the cotyledonary sheath emerged first, followed by the culms. Tubers formed and matured in about 30 days. The shoot apices of tubers each had two buds that were protected by five to seven overlapping membraneous leaf scales. When tubers sprouted the longest bud grew first. The second bud contained the culm meristem.

Strawberries (Fragaria X ananassa Duch. ‘Midway’) were grown in the field with and without the use of black plastic mulch. One to three postplant applications of glyphosate [N-(phosphonomethyl)-glycine] at 2.2, 4.5, and 5.6 kg/ha or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at 0.6, 1.1, and 2.2 kg/ha were made as directed sprays between the rows in 1976 and 1977. Glyphosate was generally more effective than paraquat for controlling weeds during the entire growing season, although both gave adequate short-term control. When late-season applications were made during 1976, a residual weed control effect was observed from both herbicides during early 1977. Crop yield, fruit size, and fruit quality were not affected by either herbicide. Similar results were obtained in a separate experiment in which strawberries were grown utilizing plastic mulch.

Cell suspension cultures of white clover (Trifolium repens L. ‘Regal Ladino’) were treated with 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], 2,4,5-TP [2-(2,4,5-trichlorophenoxy) propionic acid], and 2,4,5-TB [4-(2,4,5-trichlorophenoxy)butyric acid]. Cell population densities were monitored throughout the treatment period and herbicide remaining in the cells and culture medium was extracted and quantified at the termination of the treatment. Herbicide tolerance increased in cell populations which were conditioned by pretreatment with 2,4-DB and 2,4,5-T. However, 2,4-DB was rapidly degraded by all cell populations regardless of pretreatment. White clover cell suspension cultures treated with 2,4-D, 2,4-DB, 2,4,5-T, 2,4,5-TP and 2,4,5-TB metabolized the homologs, according to the following sequence: butyric acidåpropionic acidåacetic acid homologs. There was no difference in the rate of degradation of similar homologs of the 2,4-dichloro- and 2,4,5-trichloro- analogs.

The metabolism of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] in cell suspension cultures of white clover (Trifolium repens L. ‘Regal Ladino’) was investigated using (ring)- 14C 2,4-DB. The herbicide and its 14C-labeled metabolites were isolated from treated cells and medium after 48 h by partition and thin layer chromatography (TLC). The major portion of the radiolabel was in the glycoside fraction (47%) and incorporated into the cell structural material (34%). The remainder of the 14C remained either as the parent herbicide (8%) or an amino acid conjugate of 2,4-DB (10%).

Weed competition in the commercial production of woody ornamentals results in substantial economic losses annually due to increased labor costs and reductions in plant growth and quality. Container and field experiments were established in 1975 and continued through 1976 to evaluate oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] as a weed control agent and to determine its effect on ornamentals at selected test sites throughout the United States. Test programs were conducted with container and field grown ornamentals at 10 locations during 1975 and subsequently increased to 12 locations in 1976. Rates evaluated included 3.4, 4.5, 5.6 and 11.2 kg/ha. Highly effective control of 17 weeds was obtained for 3-month periods at rates as low as 4.5 kg/ha. Oxadiazon gave commercially acceptable control of common groundsel (Senecio vulgaris L.), a very serious weed problem in containers. Control of common chickweed [Stellaria media (L.) Cyrillo], however, was poor at all rates tested. Ornamental tolerance to oxadiazon was generally excellent. Of the 50 ornamental species evaluated in 1975, only two displayed phytotoxic symptoms; scarlet firethorn (Pyracantha coccinea Roem.) and Chinese privet (Ligustrum sinense Lour.) at 5.6 and 11.2 kg/ha following three successive applications at 3-month intervals. In 1976 trials on 63 species, phytotoxic symptoms could not be reproduced on the above species; chemical intolerance was limited to growth inhibition of aloe yucca (Yucca aloifolia L.) at 5.6 and 11.2 kg/ha.

In growth chamber studies, we measured the movement of cotyledons and leaves or leaflets in seedlings of nine weed species to determine: the magnitude of movement, whether movements followed a rhythmic pattern, and if rhythmic movements were endogenously controlled. Seedlings were always entrained under a 15-h light:9-h dark regime. Measurements were made at 3-h intervals for 3 to 4 days under four light regimes: alternating 15-h light:9-h dark; continuous light; one 15-h light:9-h dark span, followed by continuous light; and a 15-h light:9-h dark regime, in which the dark span was advanced 9 h (phase shift) when measurements were begun. No clearly defined pattern of leaf movement was found in wild mustard [Brassica kaber (DC.) L. C. Wheeler var. pinnatifida (Stokes) L. C. Wheeler]. Daily rhythmic leaf movements that did not appear to be endogenously controlled were found in redroot pigweed (Amaranthus retroflexus L.) and black nightshade (Solanum nigrum L.). Circadian rhythmic leaf movements that appeared to be under endogenous control were found in jimson-weed (Datura stramonium L.), common lambsquarters (Chenopodium album L.), common cocklebur (Xanthium pensylvanicum Wallr.), prickly sida (Sida spinosa L.), sicklepod (Cassia obtusifolia L.), and coffee senna (Cassia occidentalis L.).

Several herbicides applied either in the fall or spring at rates used for musk thistle (Carduus nutans L.) control had no deleterious effects on two cool-season grasses, smooth brome (Bromus inermis Leyss.) and intermediate wheatgrass [Agropyron intermedium (Host) Beauv.]. Herbicides used were 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, and Dowco 290 (3,6-dichloropicolinic acid). Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] was included for comparative purposes because it is known to affect the protein content of some forage grasses. Effects on the quality of the forages were measured by in vitro dry matter disappearance (IVDMD), protein and KNO3 determinations. Intermediate wheatgrass was less susceptible to damage from the highest rates of picloram and atrazine than smooth brome.

Time- and concentration-course studies were conducted to determine the metabolic sites of action of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} in isolated mesophyll cells of cotton (Gossypium hirsutum L. ‘Acala SJ-1′) and red kidney bean (Phaseolus vulgaris L.). Cotton is resistant and bean is susceptible to fluridone. The herbicide was not metabolized in cells of either species during the 2-h incubation period. At the highest concentration (10-4 M) and longest incubation time (2 h), fluridone inhibited photosynthesis, RNA synthesis, and protein synthesis 59, 56, and 32%, respectively in bean and 24, 21, and 14% in cotton. Lipid synthesis and dark respiration were only slightly affected. The lowest concentration and the shortest incubation period that inhibited photosynthesis, RNA synthesis, and protein synthesis in bean did not have any significant effect in cotton. The difference in responses may contribute to the selectivity of the herbicide. Although photosynthesis appeared to be the primary site of action, RNA synthesis was also markedly inhibited. These inhibitions and the somewhat lower inhibition of protein synthesis may ultimately contribute to the herbicidal action of fluridone in the intact plant.

Detached leaves of hemp dogbane (Apocynum cannabinum L.) were treated with 14C-glyphosate [N-(phosphonomethyl)glycine] with and without adjuvants in the treatment solution. In the absence of adjuvants, 14C absorption was not significant after the first 30 min harvest. Adjuvants increased the amount of glyphosate initially absorbed but did not extend the period of absorption. The pattern of glyphosate absorption in isolated leaf cells was similar to the pattern found in detached leaves. Significant absorption was obtained at the first 15-min sampling with no additional absorption occurring during the remainder of the 2-h incubation period. The quantity of 14C absorbed by cells was proportional to the external concentration, but the pattern of cellular absorption was unaffected by the glyphosate concentration. After 2 h of incubation, an average of 0.1% of the glyphosate had been absorbed by the leaf cells. In similar studies using 14C-leucine, 1.0% of the 14C was absorbed after 2 h with absorption still increasing in a linear fashion. A uniform distribution of 14C was obtained in detached leaves that had absorbed 14C-glyphosate through the stem. In vitro and in vivo binding studies indicated this absorbed 14C was not tightly bound to cellular components and was probably free to be absorbed by and translocated out of the cells. Since the absorption pattern in detached leaves was similar to the pattern obtained in isolated cells, cellular absorption appears to represent the major barrier in the foliar absorption of glyphosate by hemp dogbane.

Seed and tubers and dwarf spikerush [Eleocharis coloradoensis (Britt.) Gilly] survived extremely cold and hot temperatures if damp-dried before exposure. Damp-dried seed survived 14 days exposure to −196 C and 21 days exposure to 72 C, and then germinated 59 and 24%, respectively. Seed submersed in water germinated 20% when exposed to −15 C for 30 days and 4% when exposed to 60 C for 3 days. When damp-dried seed were warmed at 37 C for 21 days the germination was nearly twice that for wet seed treated similarly. Tubers that were damp-dried before exposure survived −196 C for 14 days and 49 C for 21 days and then germinated 20 and 49%, respectively. Tubers that were exposed wet to hot or cold temperatures were killed at less extreme temperatures than seed. None of the tubers exposed wet survivied −15 C for 30 days or 49 C for 3 days.

Definitions and properties of light, the effects of light on plant growth and physiological processes, and methodology and terminology for the measurement and reporting of light are reviewed. Alternatives to photometric methods now generally used in studies of the effects of light on plants in weed research are proposed. For studies of leaf energy budgets and plant water relations, the irradiance may be appropriately measured with radiometric methods and the data reported as W [watts] m-2. For studies of photosynthesis, the photosynthetic photon flux density may be measured and the data reported as μE [einsteins] m-2 s-1 or μmol [μmoles of photons] m-2 s-1. Different types of instruments are described and sources for these instruments are provided.

For 3 yr, herbicide treatments of preplant trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), postemergence diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], both herbicides, or none were superimposed on cotton (Gossypium hirsutum L. ‘Acala SJ-2′) grown on beds centered at 102 cm using a single row or two rows spaced 28 cm apart. Cotton stand, after thinning, was 5.1 plants/m in each cotton row. Herbicides controlled annual weeds regardless of planting pattern. Cultivation, without herbicides, controlled annual grass weeds much better in cotton grown in single rows than in double rows. Preplant applications of trifluralin did not influence populations of cotton plants, regardless of row pattern. Single- and double-row plots treated with trifluralin always yielded more than untreated double rows. In two of three seasons, however, single-row plots without herbicides yielded as much as those treated with trifluralin. The lower yields in the double-row cotton were associated with reduced annual grass control especially in plots not treated with trifluralin. Weed control treatments or planting patterns did not influence the occurrence of Pythium ultimum Trow or Rhizoctonia solani Kühn on cotton seedlings. The presence of Thielaviopsis basicola (Berk & Br.) Ferr. on cotton seedlings was not influenced by planting pattern but was increased by trifluralin in the third year of the study. Percentage of cotton plants with symptoms of verticillium wilt (Verticillium dahliae Kleb.) was not influenced by weed control treatments, but the percentage of diseased plants was higher in single-row than in double-row planting patterns. We attribute this response to fewer plants per hectare in single rows compared to double rows.

Adsorption of benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), profluralin [N-(cyclopropylmethyl)-α,α,α-tri-fluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) was studied in 10 Wisconsin soils. Ratios of the quantity of each herbicide adsorbed and quantities remaining in the soil solution at equilibrium (Kd value) on a Piano silt loam (Typic Argiudoll fine-silty, mixed, mesic) remained relatively constant over a range of concentrations. Herbicide adsorption by the soils was related more closely to soil organic matter than to the other soil chemical and physical properties. Diffusion of the herbicides in Piano silt loam was affected by soil water. Diffusion of trifluralin, profluralin and benefin decreased as soil water increased. Diffusion of dinitramine and fluchloralin did not change significantly with change in water content. Diffusion of oryzalin increased at the highest soil water content. None of the herbicides moved more than 10 mm in the soil during a 17-day period. In unsaturated Piano silt loam, relative mobility of the herbicides was trifluralin ≥benefin>profluralin>fluchloralin>dinitramine≥oryzalin. Oryzalin reached highest mobility in water-saturated soil.

The rate of herbicide required to reduce growth of grain sorghum (Sorghum vulgare, Per. ‘Pioneer 8417′) by 50% (GR50) and soil adsorption coefficients (Ka) were determined for the experimental herbicide, fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, in 14 soils. A linear correlation analysis was conducted between GR50 values and the chemical and physical properties and fluridone absorption coefficient (Ka) for 14 soils. The GR50 values were significantly correlated to soil organic matter and Ka. A stepwise regression analysis suggests that Ka or organic matter content can be used to predict the rate of fluridone application required for herbicidal activity.