Greenhouse hydroponic and field experiments were conducted to determine the effect of nitrogen (N) fertilizer on eastern black nightshade growth and N content. After 4 wk in hydroponics, the greatest shoot dry mass occurred in the 5 or 10 mM nitrate treatments. An exponential model was strongly correlated with eastern black nightshade root and shoot growth in the 5 or 10 mM nitrate treatments. Eastern black nightshade reached the exponential stage of growth approximately 21 d after transfer to the nitrate treatments. Root dry mass was only 10% of shoot biomass. There was a substantial increase in height and growth rate when plants were fertilized with 168 kg N ha−1. Eastern black nightshade was at its maximum growth 12 wk after planting, and fresh mass increased with N up to 336 kg N ha−1, the greatest N concentration in the study. The greatest N content was in the upper leaves and the least in the lower stem. These results indicate that eastern black nightshade growth is favored by high rates of N.

The genetic variation at 12 isozyme loci was investigated in the three species (Xanthium italicum, X. strumarium, and X. orientale) forming a X. strumarium complex in Italy. Very little variation was found within species at the loci studied in contrast to the considerable interspecies genetic differentiation at several loci. The gene differentiation between species was ranged from 61 to 91%. The observed genetic structure of the X. strumarium complex was consistent with that found for predominantly autogamous species. The values of maximum outcrossing rates estimated in original sampling sites and in a field test ranged from 8 to 17%, confirming previous observations that Xanthium species are predominantly self-pollinated. Gene duplications were evident in the three Xanthium species because of their likely polyploid origin. The percentage of duplicate loci exhibiting “fixed heterozygosity” was 25, 25, and 16% in X. italicum, X. strumarium, and X. orientale, respectively. Data presented supported that both mating system and ploidy level were fundamental features in adaptation process of investigated Xanthium species. Some evidence suggested that polyploidization occurred before speciation of X. italicum, X. strumarium, and X. orientale. As a consequence, a common ancestral progenitor could be postulated for the three species. During geographical adaptation, the three species fixed alternative alleles in some loci, and the process was favored by the predominantly autogamous mating system. On the contrary, fixed heterozygosity in duplicated loci allowed maintenance of a sufficient level of gene diversity in the three Xanthium species to ensure wide adaptability in different microhabitats (i.e., abandoned land, roadsides, and field crops) and to avoid the negative effect of inbreeding depression.

Field studies were established in 1974 and 1975 at various locations in San Diego County, CA, to evaluate several herbicides for the control of chamise (Adenostoma fasciculatum H.&A.) and redshank chamise (Adenostoma sparsifolium Torr.). Herbicide effects on vegetation were reevaluated in 1982. Plots originally treated with 2.2 or 4.5 kg ae/ha of glyphosate [N-(phosphonomethyl)glycine] had virtually no chamise regrowth 8 yr after treatment. The herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid], combinations of 2,4-D with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] or dichlorprop [2-(2,4-dichlorophenoxy) propionic acid], fosamine [ethyl hydrogen (aminocarbonyl)phosphonate], triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and picloram (4-amino-3,5,6-trichloropicolinic acid) had no long-term effects on chamise. Soil collected in 1982 from glyphosate-treated plots contained similar numbers of chamise seeds but fewer seeds of other species compared to untreated plots. Canopy cover of redshank chamise was similar in treated and untreated plots after 8 yr. These results document the effectiveness of glyphosate in killing the underground root-crown of chamise, which prevented sprouting, but not redshank chamise.

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.

Sorption and desorption of cyanazine with three Mississippi Delta soils (two silt loams and one silty clay) were studied under laboratory conditions. Cyanazine sorption calculated using the Freundlich equation was greatest for the Sharkey silty clay soil. Partition coefficients (K d values) for cyanazine sorption ranged from 1.67 to 1.82, 1.92 to 2.15, and 3.65 to 3.96 ml g−1 for the Bosket silt loam, Dubbs silt loam, and Sharkey silty clay soils, respectively. Differences in sorption and K d values were attributed to clay content. At a given initial cyanazine concentration, cyanazine was desorbed more readily from the silt loam soils than from the Sharkey clay after the first 4-h desorption cycle. Desorption from the Sharkey clay continued for a longer period than that from the silt loam soils, with up to 6% cyanazine desorption from the Sharkey clay after a 16-h desorption cycle compared with 0% for the silt loam soils. Cyanazine losses increased with decreasing clay content, Dubbs = Bosket > Sharkey. This implies a potential relationship between cyanazine desorption and surface runoff losses of cyanazine.

The etymology of herbicide has been traced to a U. S. trademark originally registered by William J. Reade of the Reade Manufacturing Company.

Field studies were conducted over 3 yr in central Spain to investigate the tolerance of common vetch and oat to some preemergence herbicides and their effects on weed control, forage yields, and botanical composition of the forage mixture. Pendimethalin was the only herbicide that injured common vetch. Pronamide and pronamide plus diuron injured oat by affecting plant emergence. Prevalent weed species were fumitory, henbit, and wild buckwheat. All herbicides provided more than 90% control of fumitory and most herbicides except pronamide provided more than 90% control of henbit relative to the untreated check. Wild buckwheat stands were reduced by isoxaben (68%), linuron (40%), prometryn (69%), pronamide (86%), and pronamide plus diuron (61%). More than 90% control of prostrate knotweed was achieved with isoxaben, pronamide, and terbutryn. Pronamide and pronamide plus diuron reduced forage yields and increased vetch in the forage. The untreated vetch and oat monocrop treatments showed the competitive advantage of oat over vetch and weedy species.

Sericea lespedeza (Lespedeza cuneata (Dumont) G. Don, var. Serala) was planted in three field experiments at three seeding rates with four rates of S-propyl dipropylthiocarbamate (vernolate). Grass and broadleaf weed populations were reduced, but sericea was unaffected by vernolate incorporated preplant. Use of a herbicide permitted a reduction in seeding rate with no decrease in sericea stand or forage yield. This treatment permitted harvesting a cutting of hay the establishment year with only a minor effect on production the next year. The beneficial effect of vernolate on sericea yield continued the second year, mainly because sericea plants were better established and more vigorous. Sericea seeding rate did not affect weed competition or forage yield. A seeding rate of 11 kg/ha with 3.4 kg/ha vernolate was the most practical treatment.

Rates of 0, 1.7, and 3.4 kg/ha of 3-amino-2,5-dichlorobenzoic acid (chloramben) were incorporated to 0, 3.8, and 7.6-cm depths in 0.7 by 0.7-m microplots under low, moderate, and high rainfall conditions. Soybean [Glycine max (L.) Merr., var. Amsoy] injury increased with increasing depth of incorporation of 3.4 kg/ha chloramben. Chloramben incorporation under low rainfall conditions significantly improved control of giant foxtail (Setaria faberii Herrm.), smooth pigweed (Amaranthus hybridus L.), and velvetleaf (Abutilon theophrasti Medic.) compared to surface treatments. Jimsonweed (Datura stramonium L.) was not controlled well by chloramben regardless of rate or incorporation depth. In larger field plots over a 3-year period, 3.4 kg/ha chloramben incorporated with a disc produced slight but insignificant soybean injury. Giant foxtail, smooth pigweed, common ragweed (Ambrosia artemisiifolia L.), and velvetleaf control with incorporated chloramben was equal to or better than the control obtained with surface-applied chloramben. Regardless of method of application, control of common cocklebur (Xanthium pensylvanicum Wallr.), jimsonweed, and annual morningglory (Ipomoea spp.) was poor.

Pretreatment of etiolated cucumber cotyledons with potassium (K), benzyladenine (BA), or δ-aminolevulinic acid (ALA) for 20 h in the dark, followed by exposure to light for 24 h, increased chlorophyll and carotenoid content. A similar treatment with fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} decreased the levels of these photosynthetic pigments. However, when the etiolated cotyledons were pretreated with either BA or ALA for 20 h in the dark, followed by fluridone during a 24-h light period, the inhibitory effects of fluridone on chlorophyll content were reversed and the values were higher than the controls. In these treatments, ALA did not counteract the inhibitory effects of fluridone on carotenoids, but BA reduced the effects. In the cucumber cotyledon greening system, K was found to be most effective in stimulating both chlorophyll and carotenoid accumulation. When K was administered to the cotyledons either together with, prior to, or after the fluridone treatment, the inhibitory effect of fluridone on chlorophyll accumulation was totally eliminated and the stimulatory effects due to K were still maintained. Although K increased carotenoid content, it did not reverse the inhibitory effect of fluridone on carotenoids. From these findings it is concluded that the inhibition of chlorophyll and carotenoid accumulation by fluridone may be mediated via unrelated mechanisms at fluridone concentrations that do not totally eliminate or drastically reduce carotenoid content.

The effect of 2,3,5-trichloro-4-pyridinol (pyriclor) on some photochemical reactions that bring about the formation of assimilatory power—the generation of adenosine-5′-triphosphate (ATP) and reduced nicotinamide-adenine dinucleotide phosphate (NADHP2)–at the expense of radiant energy has been determined using isolated spinach (Spinacia oleracea L., var. Viroflay) chloroplasts. The assimilation of carbon dioxide and cyclic photophosphorylation catalyzed by riboflavin-5′-phosphate (FMN) both showed inhibition at a rather high level of the pyridinol. However, oxygen evolution and non-cyclic photophosphorylation were strongly inhibited. Evidence is presented to support the conclusion that the locus of attack is the oxygen-evolving system and/or Pigment System 2 of the photosynthetic apparatus.

Laboratory and field experiments were conducted to describe the root system of honeyvine milkweed [Cynanchum laeve (Michx.) Pers.], and to study factors affecting the growth of plants from root fragments of shallow, ascending roots. The root system of a typical plant was composed of lateral roots radiating from a sparsely-branched, vertical taproot. Laterals tended to concentrate in a boundary area between a loamy surface soil and a zone of clay accumulation, this boundary area being below the zone of cultivation. Vertical taproots were found to a depth of 2 m, with sections collected at this and shallower depths demonstrating the ability to produce aerial shoots. In laboratory studies, root sections were killed either by freezing for 2 h or by drying at either 20 or 30 C for 24 h. The optimum temperature for shoot development from root sections was between 20 and 30 C. Shoot emergence and growth from buried root sections were generally unaffected by either depth of planting or root length. As many as 45 daughter shoots were produced from a single plant originating from seed, and 27 daughter shoots were developed from a root section 131 days after planting. The maximum distance daughter shoots were observed from original plants 131 days after planting was 111 cm.

The herbicide 4-amino-3,5,6-trichloropicolinic acid (picloram) was applied to several bermudagrasses (Cynodon spp.). Most of the grasses were susceptible to picloram; however, some were resistant and recovered within 16 months from the initial treatment. There were no detectable metabolites of 14C picloram in bermudagrass (C. dactylon (L.) Pers. ‘U-3’) or common Kentucky bluegrass (Poa pratensis L.). Also, there were no abnormal changes in cells of swollen nodes of picloram-treated bermudagrass that could explain the selective herbicidal injury of picloram on bermudagrass.

Latent infections of Colletotrichum gloeosporioides f.sp. malvae (C. g. malvae) in plants and seed were determined in several crops under field conditions after application of C. g. malvae conidia at 12 times the recommended rate. Colletotrichum g. malvae was isolated in trace amounts from Brassica napus/campestris, Linum usitatissimum, Lens culinaris, Brassica juncea/hirta, Helianthus annuus, and Triticum spp. only at the 2-wk isolation. Colletotrichum g. malvae was never isolated from Beta vulgaris. After 5 wk, C. g. malvae was not detected in any of the crops, except for Carthamus tinctorius at harvest, and was not detected from wash water of plant tissue or seed after 72 h. Colletotrichum g. malvae recovery in the field, as in controlled environmental conditions, decreased with time, which indicates that buildup of inoculum did not occur. Fungi other than C. g. malvae and bacteria isolated from seed and from wash water of plant tissue increased with time throughout the growing season. Colletotrichum g. malvae was not recovered from seed or crowns of any of the crop cultivars at either location in either growing season, except for C. tinctorius. Only one seed of the C. tinctorius cultivar ‘S-208’ out of 17,280 C. tinctorius seed analyzed over three growing seasons tested positive for C. g. malvae. Colletotrichum g. malvae was found only on the seed coat; the germinated seedling was not infected. Colletotrichum g. malvae was not recovered from any of the wash water from seed. These results should alleviate any of the concerns regarding the fate of the millions of conidia applied during a normal spray operation on nontarget plants, the potential infectivity of nontarget plants, the potential buildup of C. g. malvae in the field, and the utilization of any of the C. g. malvae-treated crops for food or feed.

A split-stem technique was devised for the rapid evaluation of herbicide effect on root growth and herbicide translocation. Four rows of adventitious root initials were prominent on the stem of red kidney bean [Phaseolus vulgaris L.] seedlings. They were excised at the soil level above the vascular plate. Excised stems were longitudinally split for a distance of 75 to 90 mm leaving two rows of root initials on each stem portion. Split-stem halves were immersed in herbicide-nutrient and nutrient solutions, respectively, contained in paired 25 by 150-mm test tubes. Subsequent plant growth and development of treated plants reflected effects of the herbicide on root growth. Herbicide translocation often was indicated by abnormalities of growth of plant tissues remote from the herbicide solution.

Maturation rate, pod production, and density of common milkweed (Asclepias syriaca L.) were determined at sites in east-central Missouri. Emergence of milkweeds in May was followed by blooming of flowers in late June, production of full-size follicles (average of 5.1 per plant) by late July, and release of seed in mid-September. Density was 1 to 3 plants per m2 and spacing of plants in 1.4 m2 samples was equidistant. Significant. positive correlations were found between mean height of milkweeds and pH, magnesium and calcium concentrations in the soil, and between density and pH of the soil.

Seven herbicides were applied for selective weed control on three different seedling stands of five cool-season grasses. The herbicides were evaluated for their influence on weed control, grass establishment, and first crop grass seed production. These experiments indicate that 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) was outstanding in selective control of broadleaf weeds in seedling grass stands. Two other herbicides, 3,6-dichloro-o-anisic acid (dicamba) and 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium ion (diquat) were valuable under most conditions. The remaining herbicides—(2,4-dichlorophenoxy)acetic acid (2,4-D), 2-sec-butyl-4,6-dinitrophenol (dinoseb), 2,3,6-trichlorobenzoic acid (2,3,6-TBA), and 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon)—were satisfactory for selective weed control under some conditions, but their effects were not uniform for the different species and plantings.

Terbacil (3-tert-butyl-5-chloro-6-methyluracil) was applied to highbush blueberry plants (Vaccinium corymbosum L. ‘Pemberton’, ‘Rancocas', ‘Jersey’, and ‘Concord’) growing in a Rifle peat, Camas clay loam, or Mossy Rock silt loam for control of quackgrass [Agropyron repens (L.) Beauv.]. Control was 80 to 100% from applications made in April after the blueberry plants broke dormancy. Higher dosages proved phytotoxic from these applications on Camas clay loam. Applications in February or March while the blueberry plants were still dormant caused no phytotoxicit; to the blueberry plants and provided 80 to 90% quackgrass control. Four consecutive yearly applications caused no residual buildup to the point of phytotoxicity to blueberry plants. Carry-over of terbacil in the soil from year to year did occur.

An application of urea to the soil of potted tomato plants (Lycopersicon esculentum Mill. ‘John Baer’) increased the translocation of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] to the shoots of the plants. The rate of uptake of atrazine was more closely related to the rate of transpiration than it was to the rate of stump exudation or root pressure. The presence of urea did not change the metabolism of atrazine by the plants. Over the range of xylem flows from 12 ml/24 h in detopped roots (root pressure) to 211 ml/24 h in intact plants (transpiration) the concentration of atrazine in the xylem stream was approximately the same suggesting that the uptake mechanism tends to maintain a constant concentration of atrazine in the xylem stream.