Selective control of red sorrel (Rumex acetosella L.) in Kentucky bluegrass (Poa pratensis L.) seed fields was obtained with 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 7-oxabicyclo(2.2.1)-heptane-2,3-dicarboxylic acid (endothall), 3-amino-2,5-dichlorobenzoic acid (amiben), 2,3,6-trichlorophenylacetic acid (fenac), and 2,3,6-trichlorobenzoic acid (2,3,6-TBA). Kentucky bluegrass seed yields and germination were not significantly reduced by application of any of the herbicides in the fall even though rates higher than necessary for red sorrel control were used. Application of dicamba in the spring at more than 1/2 lb/A reduced Kentucky bluegrass seed yields and germination. Endothall reduced seed yields when applied in the spring at 4 or 5 lb/A.

Diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl) glycine] applied posttransplant in peppers (Capsicum annuum L.) but preemergence to hairy galinsoga [Galinsoga ciliata (Raf.) Blake # GASCI] controlled the weed at 1.7 to 2.2 kg ai/ha. No serious crop injury or yield reduction was observed when diethatyl was applied to peppers at 9 kg/ha posttransplant or at bloom. Soil ridging, practiced to improve drainage and control the crown rot phase of Phytophthora blight (Phytophthora capsici L.), limited the duration of weed control by disrupting the herbicide-treated surface soil and exposing untreated soil. Diethatyl applied at 2.2 kg/ha posttransplant and again at pepper bloom, after the soil ridges were formed, controlled hairy galinsoga throughout the entire growing and harvest season.

The effect of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], desmedipham [ethyl m-hydroxycarbanilate carbanilate(ester)], propanil (3′,4′-dichloropropionanilide), and dibromothymoquinone (DBMIB) (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) on proton translocation and photophosphorylation in isolated spinach (Spinacia oleracea L.) chloroplast fragments was investigated. In the absence of added cofactors, O2, or artificial electron acceptors, cyclic electron transport occurred, which was coupled to energy conservation. Under aerobic conditions O2 acted as the terminal acceptor in non-cyclic electron transport. Proton translocation and photophosphorylation in the cyclic process were enhanced by diuron, desmedipham, and propanil, while in the non-cyclic process they were inhibited by all three herbicides. DBMIB inhibited proton translocation and photophosphorylation in both processes. Proton translocation and its enhancement increased with increasing light intensities. The finding that the plastoquinone (PQ) antagonist DBMIB disrupted cyclic as well as noncyclic electron flow, while diuron enhanced the cyclic and inhibited the noncyclic process, indicated that the acceptor site for endogenously-cycling electrons must lie between the active site of diuron inhibition and PQ, The close similarity in the behavior of diuron, desmedipham, and propanil suggests that their site of action is the same.

The effect of soil matric potential from −0.02 to <–1.5 MPa on Texas panicum growth in drainage lysimeters covered by an automatic rainfall shelter was measured in 1984, 1985, and 1986. Rate of tiller production was faster for plants established in April than June in 1984 and 1985, but not 1986. In 1985 and 1986, dry weight was greater, but total seed production was less for plants established in April than June. Irrigation when the soil matric potential was −0.02, −0.075, or −1.5 MPa did not affect rate of tiller production in 1984. Irrigation when the soil matric potential was −1.5 MPa decreased dry weight of plants but increased seed number per panicle compared to irrigation when the soil matric potential was −0.02 MPa in 1985 and 1986. Plants grown in lysimeters irrigated at soil matric potential <–1.5 MPa in 1985 and 1986 did not wilt at 8:00 a.m.; therefore, they were not watered after establishment. These nonirrigated plants averaged 0.9 and 0.4 kg dry weight and produced 92 200 and 16 100 seeds in 1985 and 1986, respectively.

Tolerance of corn (Zea mays L. ‘B’), cotton (Gossypium hirsutum L. ‘coker 413’), soybean (Glycine max Merr. ‘Hardee’), turnip (Brassica rapa L. ‘Tendergreen’), sorghum (Sorghum bicolor (L.) Moench. ‘Georgia 615’), purple nutsedge (Cyperus rotundus L.), yellow nutsedge (C. esculentus L.), and johnsongrass (Sorghum halepense (L.) Pers.) to 2,6-dichlorobenzonitrile (dichlobenil) at 0, 0.14, 0.28, 0.56, 1.12, and 2.24 kg/ha in four Georgia soils was determined. Equivalent rates of dichlobenil generally were more toxic in Davidson clay loam which had the highest clay content. Crop tolerance was corn > sorghum > cotton > turnip. Purple and yellow nutsedge tolerance to dichlobenil was intermediate to that of the crops tested. Johnsongrass response was equivalent to that shown by sorghum.

Experiments were conducted to determine the influence of water depth, fall flooding, and burial depth on the development of common waterplantain (Alisma triviale Pursh. # ALSPA) in wild rice (Zizania palustris L.). The optimum water depths for common waterplantain from corms were 20 cm when grown outside in submerged pots at St. Paul and 2 and 15 cm when grown in a sloping field at Grand Rapids. Growth of common waterplantain from seeds was maximum at the lowest water depths (2 to 7 cm) at both locations. Wild rice dry weight and seed yield in the same experiments were maximum at the 20- and 30-cm water depths at St. Paul and the 15- and 28-cm depths at Grand Rapids. The increased wild rice seed yield and dry weight at these depths was related to increased tiller production. Wild rice yield was similar at all water depths at Grand Rapids when grown with common waterplantain from corms at a density of 11 plants/m2. Water depths that decreased the effect of common waterplantain interference with wild rice, reduced wild rice yield. Establishment of common waterplantain from corms was maximum at the 5- and 15-cm depths and was severely reduced at the 0- and 30-cm soil depths in soils not flooded in the fall but flooded in the spring. Fall flooding killed all corms regardless of burial depth. Corm mortality under fall-flooded conditions may be due to the effects of ice-encasement.

Two, 4-dichloro-6-fluorophenyl-p-nitrophenyl ether (CFNP) is similar in herbicidal property and chemical structure to nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether). CFNP inhibits the growth of the hypocotyl and young buds of germinating weeds. Henry Crabgrass (Digitaria adscendens H.B.K. Henr.) was controlled by CFNP at 0.5 kg/ha, however sunflower (Helianthus annuus L.) was tolerant to 16 kg/ha of CFNP. CFNP also effectively controlled largeseed dodder (Cuscuta indecora Choisy) which is a serious problem in sunflower. Although trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) did not control common dodder at 8 kg/ha, CFNP gave control at 0.5 kg/ha.

Combinations of antagonistic herbicides can be helpful in the search for seed-applied chemical safeners to protect crop plants from herbicide injury. If a particular herbicide combination is selectively antagonistic so that the crop is not injured but weed control efficacy is not reduced, it should be possible to develop a new, more selective formulation of the herbicide which includes the antagonist or antidote. A promising new approach involves the use of early pretreatments of crop plants with subtoxic levels of a particular herbicide to increase crop tolerance to later, higher rates of that herbicide. When there are different mechanisms for herbicide detoxification in different plant species, it should also be possible to develop selective herbicide synergists that would provide equal efficacy at lower rates with greater crop tolerance. As our knowledge of herbicide metabolism and mode of action develops, it will be increasingly possible to use other chemicals to selectively synergize or safen herbicides to solve problems in important crop-weed situations.

The persistence of 2,4-D [(2,4-dichlorophenoxy) acetic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] was studied in the chaparral environment. Chamise (Adenostoma fasciculatum H. & A.), grass and forbs, soil surface litter, and soil were sampled for up to 360 days after herbicide (4.5 kg/ha) application. Over 50% of the 2,4-D and 2,4,5-T recovered was found on soil surface litter while 18 to 31% was found on vegetation. Much less herbicide (0.1 to 0.2%) was found in soil (0 to 5 cm) than in foliage or litter. No herbicide residues were found below the 0 to 5 cm soil sample zone. Herbicide residues on foliage and litter decreased rapidly (up to 93%) within 30 days after application but remained constant thereafter until winter rainfall began. Residues of both herbicides were evident in chamise foliage (0.01 to 0.02%), surface litter (0.01 to 0.03%), and soil (0.01%) up to 360 days after application.

Reliable estimates of weed fecundity require determination under ranges of management practices such as differing crops and tillage systems. We measured components of reproductive output per plant (numbers of primary tillers, panicles, and seeds; and sizes of panicles) in three emergence cohorts of green foxtail and yellow foxtail growing among corn and soybean in moldboard plow (MP), chisel plow (CP), ridge till (RT), spring disk (SD), and no till (NT). Differences in emergence between crops and foxtail Cohorts 1, 2, and 3 were 5, 0, and −7 d, respectively. In MP, Cohort 1 of green foxtail produced 2.3 primary tillers and 5.6 panicles per plant, and Cohort 1 of yellow foxtail produced 4.6 primary tillers and 9.0 panicles per plant. Panicle size was variable for both species across tillage systems, crops, and cohorts both years. Green foxtail plants produced the most seeds per plant (3,811) in NT corn, and cohorts did not vary greatly, whereas fecundity was highly variable across tillage systems and cohorts in soybean, where it averaged 3,240 (± 388) seeds per plant. Green foxtail seed number per plant were closely related to panicle numbers per plant for each year in corn (r 2 = 0.90) and soybean (r 2 = 0.78), and the relationship did not vary among tillage systems. Yellow foxtail seed number per plant was closely related to panicle number per plant, and it was specific for each tillage system in corn (r 2 = 0.60 to 0.85) and soybean (r 2 = 0.65 to 0.92). Estimates for vegetative and reproductive growth were more reliable for green foxtail than for yellow foxtail across tillage systems, crops, cohorts, and years.

A technique was developed for evaluating the stability of a herbicide suspended in nitrogen solutions of varying molarity. Dispersion stability is expressed as the difference in specific gravity (D value) between a salt solution + herbicide and the salt solution alone using a Westphal balance. The lower the D value, the less herbicide in suspension. Even very low molar solutions significantly lowered the D value. Further, the lower the percent active ingredient in the herbicide the more effectively the surfactants, and possibly other components of the formulated product, offset the adverse effect of salt on dispersion stability.

Nontoxic concentrations of 2,4-D [(2,4-dichlorophenoxy)acetic acid] increased the toxicity of ametryne [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine], when applied to the roots of waterhyacinth [Eichornia crassipes (Mart.) Solms], when applied to the roots or foliage of corn (Zea mays L.), and to a lesser extent, when applied to the roots of soybean [Glycine max (L.) Merr.]. Nontoxic concentrations of 2,4-D frequently also increased the absorption of ametryne, water, and radioactive calcium by all three species. Mixtures containing toxic concentrations of 2,4-D with ametryne were not synergistic and sometimes the mixtures were less toxic than ametryne alone. Toxic concentrations of 2,4-D also decreased plant dry weight and the absorption of ametryne, water, and calcium. Low concentrations of ametryne increased the absorption of water and sometimes calcium while high concentrations decreased dry weight and the absorption of water and calcium.

Latin America is a region of contrasts including mountains and valleys, deserts and jungles, forests and prairies, prosperous and poor, modern and traditional, small farms and huge ones, malnourished and well-fed, machines and manpower, herbicides and machetes. Any country from Mexico to Chile would provide examples of these contrasts. The countries share a common heritage of language, culture, religion, and education. Each is unique in its present developmental stage and future plans (6).

Picloram (4-amino-3,5,6-trichloropicolinic acid) injected directly into a small, central-Arizona stream was lost by normal stream flow actions, such as the mixing of fast- and slow-moving water, and the interchange of surface and subsurface water in gravel and sand beds along the stream. Picloram was injected at a concentration of 6.26 ppmw; the maximum amount detected was 2.362 ppmw at 0.4 km downstream, 0.943 ppmw at 0.8 km, 0.316 ppmw at 1.6 km, 0.014 ppmw at 3.2 km, 0.001 ppmw at 6.4 km, and none further downstream. Picloram was detected near the limits of detection (0.001 to 0.004 ppmw) 2 days after injection at the 0.4-, 0.8-, and 1.6-km sites. In photodegradation tests, sunlight decomposed 57% of the picloram in containers after 8.8 h of exposure.

The antagonistic effect of Na-bentazon on sethoxydim absorption and herbicidal activity has been documented. The addition of ammonium sulfate (AMS) with a surfactant overcomes the observed loss of sethoxydim activity. Nuclear Magnetic Resonance (NMR) was used to study the chemical effects of commercially formulated Na-bentazon, NaCl, NaHCO3, Na-bentazon plus AMS, and NaHCO3 plus AMS on commercially formulated sethoxydim. Technical grade Li-sethoxydim and sethoxydim were analyzed and 1H-NMR spectra were used as comparative standards. Data indicate an association of Na+ from Na-bentazon, NaHCO3, and NaCl with the sethoxydim molecule. NH4+ from AMS appears to associate spatially with sethoxydim but does not exert the same electronic effect on the sethoxydim ring protons as observed with Na+ or Li+. The addition of AMS to sethoxydim plus Na-bentazon or NaHCO3 treatments prevents the complexation of Na+ with the sethoxydim molecule. The data support the hypothesis that the observed Na-bentazon antagonism and ammonium sulfate reversal of antagonism are chemically based.

Western ironweed (Vernonia baldwini Torr.) seedlings emerge from an exalbuminous achene. By 6 days after germination, a cortical collar was discernible between the hypocotyl and root. A pair of lateral buds arose exogenously from the outer two to three layers of this zone through dedifferentiation of cortical parenchyma. Sprouting of lateral buds could be stimulated in a few seedlings by 15 days after germination if they were clipped between the cotyledons and the hypocotyl-root transition zone. One of the seedling buds could be activated by top removal up to 40 days after germination when both could be stimulated to sprout. Ability to form new stems vegetatively was reflected in rate of anatomical maturity of the seedling buds.

The chloro-substituted benzoic acids discussed in this paper have been evaluated experimentally as soil sterilizing herbicides for field bindweed (Convolvulus arvensis L.) control at the Ft. Hays Experiment Station since 1955. The value of soil sterilization in a perennial weed control program in the Great Plains region is evidenced by recommendations made by several state experiment stations. Prior to 1950, most semi-permanent soil sterilization was accomplished with such chemicals as sodium chlorate, boron compounds, and arsenicals. These compounds continue to be important even though the poisonous qualities of arsenic compounds and the hazards of handling sodium chlorate are well recognized.

Experiments involving the application of nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] at 0.56, 1.12, or 1.68 kg/ha on each of three successive plantings of pickling cucumbers (Cucumis sativus L. ‘Explorer’) were conducted during a 2-yr period. Residues of nitralin in soil increased with rate and number of applications. Nitralin residues accumulated to higher concentrations in a soil with 2.9% organic matter than in a soil with 0.7% organic matter. However, cucumber plants were injured less in the soil with the highest concentrations of herbicide. Oats (Avena sativa L. ‘Carolee’) planted following cucumbers were injured by nitralin residues resulting from the highest application rates. Bioassays and chemical analyses suggested that no appreciable soil residues of nitralin remained during the succeeding year.

Acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} and bentazon [3-(1-methylethyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] plus acifluorfen were applied through hydraulic flat-fan nozzles or controlled-droplet applicators (CDA) in water plus surfactant, soybean [Glycine max (L.) Merr.] oil and water emulsions, and soybean oil alone. Except for inadequate weed control with CDA applications at 7 L/ha, method of application did not affect weed control of common cocklebur (Xanthium strumarium L. #3 XANST) or smooth pigweed (Amaranthus hybridus L. # AMACH) at high rates of bentazon plus acifluorfen (560 plus 280 g ai/ha or above). With low rates (280 plus 140 g/ha or less), hydraulic flat-fan nozzles were more effective than CDA applications. Early CDA applications of acifluorfen in an oil carrier at a volume of 9 L/ha were as effective as hydraulic nozzle applications at a carrier volume of 47 L/ha. Later applications resulted in inadequate weed control. Increasing soybean oil concentration from 2.5 to 40% (v/v) in acifluorfen spray mixtures did not significantly increase the phytotoxicity of acifluorfen.

Plots of western false hellebore (Veratrum californicum Durand), treated in 1968 and 1969 with 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 kg/ha, were reexamined in July 1979 to determine vegetative changes, especially any increases in the production of desirable species and long-term control of western false hellebore. Grass, sedge, and rush production had doubled, and broadleaved plant production, excluding western false hellebore, which was eliminated, decreased on treated plots. Western false hellebore had not reinvaded the treated plots; control remained at 100% for 10 yr. Removal of the western false hellebore on treated plots allowed an increase in grass, sedge, and rush production of 1,500 kg/ha over check plots.