Puccinia obtegens (Link) Tul., an autoecious rust pathogen, is a potential biological control agent of Canada thistle [Cirsium arvense (L.) Scop.]. Ten ecotypes of Canada thistle were inoculated with uredospores of P. obtegens and sporulation was observed on all ecotypes. Infection types varied among and within ecotypes, indicating that host-resistance is one factor limiting rust infection. No correlation was found between Canada thistle susceptibility to the rust and host plant ecotype classification, stomatal density, amount of leaf pubescence, or spore germinability on leaf surfaces.

The ability of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] to establish and develop from seed was studied in laboratory and field experiments. Optimum germination temperature was 30 C. Seed incubated at cooler temperatures and then transferred to 30 C germinated equally as well as seed incubated continually at 30 C. Germination was unaffected at moisture stress levels between 0 and −4.6 bars, but was decreased at levels between −4.6 and −12.8 bars. The optimum pH range for germination was between 5 and 7. The greatest emergence of seedlings occurred at a depth of 0.5 cm with no emergence occurring at depths greater than 5 cm. Greater emergence was obtained with a loam than sandy loam at all planting depths except 0.5 cm. Field plots seeded on May 1 gave maximum seed production. Seed production decreased with each 2-week delay in planting. Planting dates of July 10 or later produced no seed. Seed germination was affected little by delayed planting. The following spring, regrowth from plants seeded on June 12 or later was less vigorous than regrowth from plants seeded earlier.

An isolate of Fusarium lateritium (Nees) emend. Snyder and Hansen was associated with naturally occurring disease of spurred anoda [Anoda cristata (L.) Schlecht.] and prickly sida (Sida spinosa L.) plants. In greenhouse inoculation studies, the Fusarium isolate was pathogenic to healthy spurred anoda and prickly sida plants. The disease symptoms were characterized by leaf, stem, and root lesions. The stem lesions enlarged with time and formed cankers that often girdled the stems and killed inoculated plants. In host-range studies, velvetleaf (Abutilon theophrasti Medic.), Venice mallow (Hibiscus trionum L.), okra [Abelmoschus esculentus (L.) Moench], and hollyhock [Althaea rosea (L.) Cav.] were also susceptible to the pathogen. This is the first report of these six species as hosts for this pathogen. Corn (Zea mays L.), cotton (Gossypium hirsutum L. and G. barbadense L.), soybean [Glycine max (L.) Merr.], and 18 other representative crop and weed species in eight families were resistant to the pathogen. F. lateritium may be a useful biological herbicide for susceptible malvaceous weeds.

Sublethal amounts of 2,4-D [(2,4-dichlorophenoxy) acetic acid] were applied to several vegetable crops in order to determine effect on yield and quality in a simulated drift experiment. Tomato (Lycopersicon esculentum Mill.) and root crops were most sensitive to 2,4-D; as little as 2.1 g/ha of acid distorted tomato fruit shape and elongated radish (Raphanus sativus L.) roots. All root crops were rendered unmarketable by 10.4 g/ha and gross yields were reduced by exposure to 104 g/ha. Yield of peppers (Capsicum frutescens L. var. grossum) was increased by exposure to 2.1 g/ha and severely depressed by 104 g/ha. Cucumber (Cucumis sativus L.) fruit shape was distorted at 11 g/ha and yield was reduced slightly. Lettuce (Lactuca sativa L.), onion (Allium cepa L.), and cabbage (Brassica oleracea L. var. capitata) were least sensitive to 2,4-D. Exposure to 20.8 g/ha did not reduce yields of lettuce or cabbage. Onion yields were reduced by application of 104 g/ha. Bush bean (Phaseolus vulgaris L.) yield was decreased by exposure to 22 g/ha, but potato (Solarium tuberosum L.) yield increased at 16 g/ha. Herbicide residues in the crop foliage were proportional to the degree of exposure. Residue analysis combined with foliar symptoms may be useful in predicting crop damage following 2,4-D drift.

Control of common milkweed (Asclepias syriaca L.) with postemergence herbicides was investigated in greenhouse and field experiments. In greenhouse experiments, amitrole (3-amino-s-triazole), dicamba (3,6-dichloro-o-anisic acid), glyphosate [N-(phosphonomethyl)glycine], and combinations of amitrole + dicamba, dicamba + 2,4-D [(2,4-dichlorophenoxy) acetic acid], glyphosate + 2,4-D, and glyphosate + dicamba reduced regrowth of 6-week-old common milkweed as compared with the untreated check. Postemergence herbicides commonly used in corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and soybeans [Glycine max (L.) Merr.] had little effect on emerged common milkweed. Removal of common milkweed top-growth as early as 1 day after treatment did not effect subsequent growth reduction from glyphosate at 0.3 kg/ha or higher. In the field, satisfactory control (70% or better) of common milkweed was obtained with glyphosate at 2.2 kg/ha applied at the early or late bud growth stage. Plots plowed 1 day after application of glyphosate at 2.2 kg/ha still retained satisfactory control of common milkweed 1 yr after treatment. Herbicides applied with a herbicide glove or a roller applicator resulted in common milkweed control similar to that obtained from broadcast spray applications.

Common sunflower (Helianthus annuus L.) interference in onions (Allium cepa L. ‘Yellow Granex PRR’) was studied at different weed densities and periods of interference. Onion yields were reduced when the highest density (360/m2) of common sunflower interference with onions from 6 weeks after emergence and when sunflower at densities of 50/m2 and 5/m2 interfered for 12 and 15 weeks after emergence, respectively. Yield was not reduced if the crop was kept weed-free for 2 to 12 weeks after emergence with the shortest weed-free periods of 2 and 6 weeks requiring high light irradiance and high soil temperature and intermediate soil moisture. Climatic factors were more useful than weed density in explaining differential interference of sunflower in onions. Onion yield was negatively linearly correlated (P<0.05) with sunflower fresh weight, but was not linearly correlated with sunflower height.

Absorption, translocation, and metabolism of foliar-applied ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulphonate] were studied to explain field observations showing differences in susceptibility among sugarbeet (Beta vulgaris L.), common ragweed (Ambrosia artemisiifolia L.), redroot pigweed (Amaranthus retroflexus L.), and common lambsquarters (Chenopodium album L.). In laboratory studies, two- to four-leaf seedlings of the highly susceptible species, redroot pigweed and common lambsquarter, absorbed greater amounts of 14C-ethofumesate from foliar application than the moderately susceptible common ragweed and tolerant sugarbeet. Sugarbeet translocated very little 14C from treated foliage to untreated plant tissue. All weed species translocated 14C-ethofumesate to untreated leaf tissue when 14C-ethofumesate was applied to seedlings at the two-leaf stage. Ethofumesate was translocated basipetally to the stem and root of two-leaf redroot pigweed and common lambsquarter seedlings. A high percentage of the 14C was found in the water-soluble fraction in sugarbeet seedlings, indicating inactivation. The amount of metabolites recovered in the non-polar fraction depended on the stage of plant growth. Total photosynthesis and respiration in redroot pigweed was inhibited 4 h after foliar application and did not recover after 96 h. Uptake and evolution of CO2 were also inhibited in sugarbeet leaves, but they recovered rapidly, depending on age of plant at treatment. The stage of plant development was the key factor determining species response to foliar treatments of ethofumesate in terms of absorption, metabolism, and total photosynthesis and respiration.

Bromacil (5-bromo-3-sec-butyl-6-methyluracil), glyphosate (N-phosphonomethylglycine), picloram (4-amino-3,5,6-trichloropicolinic acid), simazine [2-chloro-4,6-bis (ethylamino)-s-triazine], and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] were evaluated at four application rates and five application dates, May 1, June 1, July 1, August 1, and September 1, for their ability to control seven herbaceous, forest ground covers, hayscented fern (Dennstaedtia punctilobula (Michx.) Moore), New York fern (Thelypteris noveboracensis L.), short husk grass (Brachyelytrum erectum Schreb.), bracken fern [Pteridium aquilinum (L.) Kuhn var. latiusculum (Desv.) Underw.], wild oat grass (Danthonia compressa Aust.), rough goldenrod (Solidago rugosa Mill.), and flattop aster (Aster umbellatus Mill.) without residual effects on black cherry (Prunus serotina Ehrh.) seed stored in the forest floor, or on survival and growth of natural or planted black cherry seedlings. Control of most of the target species depended on the date and rate of application. Simazine had no herbicidal effect on these extremely acid (pH 3.9 to 4.4) Allegheny Plateau sites. None of the herbicides interfered with germination of black cherry seed stored in the forest floor or with establishment of seedlings. Bromacil applied at 22.4 kg/ha, picloram, at 9.0 kg/ha, and hexazinone at 13.4 kg/ha reduced survival, or growth, or both, of black cherry seedlings planted in a forest opening. Glyphosate was the most economical herbicide that met the control criteria. Application of 1.1 kg/ha between August 1 and September 1 produced acceptable control of all target species for at least 3 yr.

Field research was conducted in 1973, 1974, 1977, and 1978 to compare water-culture practices and rates of molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate) for control of “strawhull” red rice (Oryza sativa L.) in water-seeded rice (O. sativa L.). Water-culture treatments (continuously drained, alternately drained and flooded, or continuously flooded during the first 28 days after seeding) alone, or preplant, soil-incorporated treatments of molinate (3.4, 4.5, and 6.7 kg/ha) alone did not control red rice. Treatments of preplant-incorporated molinate at 4.5 and 6.7 kg/ha in a continuously flooded culture or 6.7 kg/ha in an alternately drained-flooded culture controlled 87 to 93% of the red rice and permitted production of satisfactory yields of high quality rice grain.

The newly developed herbicide buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadizol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} was studied with respect to its interaction with soils and homoionic clay minerals and its response to irradiation with ultraviolet light. Results showed that it could enter the interlamellar spaces of swelling clays such as smectite. Isothermic adsorption studies indicated that Cu+2-smectite adsorbed more buthidazole than Cu+2-kaolinite. The Cu+2-clay adsorption isotherm fitted the Langmuir model. The effect of exchangeable cations on adsorption was not significant in soils of high organic matter content. Bioassay studies indicated that buthidazole's phytotoxicity was not decreased in either clays or in organic soils. Infrared spectroscopic studies showed the coordination of buthidazole with Cu+2 through C=O Cu interaction with buthidazole resulted in a ligand-to-metal ratio to 1:1. Protonation of buthidazole occurred in Al+3-and H+-smectite. The herbicide was labile to UV-light irradiation at 254 nm but not at 366 nm. The photoconversion indicated a first-order reaction. The photolytic product(s) included the –N=C=O structure. Copper(II) ions, which form complexes, retarded photolysis of buthidazole in UV-light, but the Ca+2 ion, which is unable to form complexes, did not.

Mixtures of annual weeds emerging 1 week after and competing all season with potatoes (Solanum tuberosum L.) reduced tuber yields by an average of 54% compared to 16% in comparable treatments in which weeds emerged 3 weeks after potatoes. Weeds reduced tuber yields 19% 8 weeks after potatoes emerged and 25 to 45% 10 weeks after emergence. After full-season competition, for each additional 10% of the total dry biomass represented by weeds, there was a decrease of 12% in fresh tuber yield. This relationship was not valid if potatoes were harvested early, which reduced the deleterious effect of weeds on potato yields. Weed competition reduced both size and number of tubers, but had little effect on specific gravity of tubers. In some instances, the reduction in tuber size by weeds reduced the percentage of tubers that were marketable.

Laboratory studies were conducted to investigate the possibility that herbicide runoff from treated fields might be adversely affecting submersed aquatic plants in the Chesapeake Bay. In laboratory studies, I1 and I50 values (the concentrations inhibiting growth 1 and 50%, respectively) were calculated for three herbicides and several aquatic plants. Exposure periods varied from 3 to 6 weeks, with the 3-week exposure being most common. For atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], I1 values were usually a few parts per billion (ppb), whereas I50 values varied from ca. 80 ppb for elodea (Elodea canadensis Michx) to ca. 1040 ppb for Eurasian watermilfoil (Myriophyllum spicatum L.). The toxicity of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] was similar to that of atrazine. Glyphosate [N-(phosphonomethyl)glycine] was essentially non-toxic. Interactions between salinity and atrazine were studied using the brackish water species, vallisneria (Vallisneria americana Michx.). Increasing salinity did not affect atrazine toxicity. When atrazine was present in both the hydrosoil and water, the concentration in the water determined the toxicity. At concentrations below 1000 ppb, atrazine in the hydrosoil did not adversely affect the plants. Based on the results of these studies, and the known concentrations of herbicides in runoff water, these herbicides do not appear to pose any threat to the species tested.

Aspects of the life history and population dynamics of the Platte thistle (Cirsium canescens Nutt.), a rangeland weed, were studied in the Nebraska Sandhills from 1977 through 1979. This thistle is a monocarpic perennial, reproducing only by seed production, which typically occurs in small, scattered groups of plants. Seedling mortality at four sites was 75% during the first year, mostly because of dry moisture conditions. In plots with good vegetative cover, thistle rosette plants had a lower mortality rate, but growth rate was slower than that of rosette plants in plots with sparse vegetative cover. Seed heads developed during May and June and gained more than one-half of their dry weight shortly before maturing. Plants averaged 72, 197, and 303 seeds at three sites. Within sites, plants produced seeds in proportion to the number of seed heads per plant. Although naturally occurring biological-control agents have little effect on the vegetative growth phase of the life cycle, they greatly reduce the production of seeds.

Absorption experiments were conducted with tomato (Lycopersicon esculentum Mill. ‘VF-315’) seedlings using salts at the approximate ratio found in saline irrigation water (NaCl 41.9 mM, CaCl2 20.9 mM, and MgCl2 · 6H2O 10.5 mM) in combination with two herbicides. The osmotic pressure of this salt solution is 0.40 MPa (mega Pascal), which is equivalent to 4.0 bar or about 4.0 atm. EPTC (S-ethyl dipropylthiocarbamate) at 0.25 mM reduced the residual Na+, Ca2+, and Mg2+ content relative to the treatment with salts alone. CDEC (2-chloroallyl diethyldithiocarbamate) at 0.1 mM produced similar effects for Na+ and Ca2+. The addition of salts to either EPTC or CDEC induced significantly higher concentrations of total and residual herbicide in the tomato seedlings. The data suggest that salts reduce the tolerance of tomato to EPTC and CDEC by increasing absorption of the herbicides. The residual EPTC or CDEC in the tomato seedlings increased as the CaCl2 concentrations increased in the incubation medium. A strong linear relationship was found between the calcium content and EPTC or CDEC content in the tomato seedling tissue.

Napropamide [2-(α-napthoxy)-N,N-diethylpropionamide] inhibited root and shoot growth in corn (Zea mays L. ‘NC+ 59’) and tomato (Lycopersicon esculentum Mill. ‘Niagara VF315’) seedlings. Shoot growth was reduced less than root growth in both species. Corn roots were approximately 10 times more sensitive to napropamide than were tomato roots. Translocation of napropamide from the roots to the shoot of tomato occurred within 0.5 h and followed an apoplastic pattern. Little movement of napropamide from the roots to the shoots occurred in corn. Metabolism of napropamide was not evident in either species during an 8-h exposure. Absorption studies showed that total napropamide levels were 60% higher in corn root tissue than in tomato root tissue. The greater napropamide content in the corn roots was associated with a tightly bound fraction of the total napropamide influx.

The application of 2,4-D [(2,4-dichlorophenoxy) acetic acid], at 1.1 kg/ha to common dandelion (Taraxacum officinale Weber) resulted in 40% or less survival in lawn and hayfield habitats, in both spring and fall treatments. A significantly lower incidence of regeneration (12 to 20%) was attained independent of the season by shoot removal (spudding) combined with 2,4-D in the lawn, but not in the hayfield habitat. No measure of control was obtained by spudding alone, confirming the high capacity of common dandelion for root regeneration. Removal of leaves 2 weeks after application of 2,4-D diminished the effectiveness of control in both lawn and hayfield habitats, with 49 to 50% and 60 to 70% regeneration, respectively. Apparently, there is incomplete translocation of the herbicide within this interval. Significant mortality from spudding alone was observed only in plants less than 4 months old (64% survival). One-year-old plants responded to all treatments in the same manner as common dandelion populations as a whole. Optimum control of common dandelion in lawns was obtained by 2,4-D application in combination with spudding, during the spring.

Rhizome johnsongrass [Sorghum halepense (L.) Pers.] in late-planted soybeans [Glycine max (L.) Merr. ‘Forrest’] was effectively controlled with glyphosate [N-(phosphonomethyl)glycine] applied twice by a rope-wick applicator at 0.1 kg/ha each time. At crop maturity, wick-applied glyphosate controlled an average of 92% of the johnsongrass over a 2-yr period as compared to 51% where 2.2 kg/ha of glyphosate was applied conventionally to rhizome johnsongrass prior to planting. There was no difference in soybean yields and no visible injury to soybeans. Rhizome johnsongrass and volunteer corn (Zea mays L.) were effectively controlled in soybeans planted at the proper time with glyphosate applied by either the rope-wick applicator or recirculating sprayer. Soybean yields were reduced more when volunteer corn was treated with glyphosate that was applied with a recirculating sprayer than with a rope-wick applicator. This reduction in yield was attributed to splattering of the herbicide.

Applications of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] at rates from 0.3 to 1.4 kg/ha were made in the field to soils of 2 and 30% (w/w) soil moisture. After 2 to 4 days, all soils were irrigated to establish stands of either sweet corn (Zea mays L. ‘Jubilee’) or winter wheat (Triticum aestivum L. ‘Stephens’) used as bioassay species for ethofumesate activity. Ethofumesate, at most rates, was significantly less effective on both corn and wheat when applied to dry soil than to wet soil. In greenhouse studies, ethofumesate activity was significantly greater when incorporated into soil of 12% than 2% (w/w) moisture 2 or 4 days prior to irrigation. An increase in herbicide activity was apparent as the length of time between herbicide application and wetting increased from 2 to 4 days. Analysis of wet (20%, w/w) and dry (2%, w/w) soils treated with equal levels of ethofumesate revealed no loss of herbicide applied to wet soil over a 12-day period, but in the dry soil, the amount extracted after 12 days was 10% of the amount extracted at 0 days. These data and other considerations suggest that chemical degradation of ethofumesate is the most likely mechanism for the activity loss in dry soil.

Growth chamber studies and field trials were conducted to evaluate the toxicity of glyphosate [N-(phosphonomethyl)glycine] and certain other herbicides to wild garlic (Allium vineale L.). Toxicity to wild garlic increased with increasing rates up to 6 kg/ha. Glyphosate was more toxic to wild garlic when applied in spray volumes of 125 to 500 L/ha than in greater volumes. Addition of surfactant did not increase toxicity or absorption rates of 3 kg/ha of glyphosate, but did increase the advantage of 2 kg/ha of glyphosate over 2,4-D [(2,4-dichlorophenoxy)acetic acid]. When glyphosate was sprayed on wild garlic plants at 3 kg/ha, then washed off after 2, 4, 8, 16, and 32 h, absorption of a biologically significant amount of glyphosate required 8 h, and toxicity increased through the 32-h exposure. Injury, which increased as mowing was delayed up to 12 days after application, indicated that significant quantities of glyphosate were translocated between 3 to 12 days after treatment in a field test. Glyphosate; 2,4-D; 2,4-D + mecoprop {2-[(4-chloro-o-tolyl)oxy] propionic acid} + dicamba (3,6-dichloro-o-anisic acid); and VEL-4207 [N-phenyldiethanolamine-bis-(2-methoxy-3,6-dichlorobenzoate)], applied in a sequence of either spring-fall-spring or fall-spring, were compared for wild garlic control. All herbicides tested controlled wild garlic, but glyphosate was more effective than 2,4-D after spring-fall-spring applications. All spring-fall-spring treatments except 2,4-D + mecoprop + dicamba significantly reduced the number and weight of hardshell bulbs present 8 weeks after the last treatment. The initial treatment in the spring-fall-spring sequence was necessary to reduce hardshell bulb populations the second spring. One year after treatment wild garlic reinfested all plots.

The effect of 1.0 ppmw fluridone {1-methyl-3-phenyl-5-[3-trifluoromethyl)phenyl]-4(1H)-pyridinone} on growth of American pondweed (Potamogeton nodosus Poir.) and sago pondweed (Potamogeton pectinatus L.) was examined in plants kept in darkness or under various numbers of 12-h photoperiods. When plants were exposed to 1.0 ppmw fluridone for 1 to 10 12-h days, no stunting of American pondweed occurred until 21 days after treatment. Thirtythree days after treatment, plants that had received 4 to 10 days' exposure were most stunted. Sago pondweed was slightly more susceptible than American pondweed (87% and 50% reduction in length, respectively) 37 days after a 10-day exposure. Chlorophylls a and b were significantly lower in both species 14 days after all fluridone treatments. American pondweed plants exposed to fluridone continuously (1.0 ppmw) for 15 days, but given 0, 3, 6, 9, 12, or 15 12-h days were stunted only after having received at least six photoperiods. Stunting in sago pondweed was only slightly light-dependent. Neither species absorbed significantly more 14C-labeled fluridone after 2, 4, or 14 photoperiods compared to plants kept in darkness for the same time.