In controlled-environment chambers at 29/33 C day/night and 1000 μE·m-2·s-1 photosynthetic photon flux density (PPFD), increasing the CO2 concentration from 350 to 675 ppm (v/v) did not affect leaf area or total dry weight of well-watered plants of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG], goosegrass [Eleusine indica (L.) Gaertn. # ELEIN], or southern crabgrass [Digitaria ciliaris (Retz.) Koel. # DIGSP] after 30 days. However, the whole plant transpiration rate per unit leaf area decreased, and the water use efficiency increased, in response to CO2 enrichment. In a subsequent experiment, with water availability limited by an imposed drought, CO2 enrichment reduced the effects of water stress and significantly increased leaf area and total dry weight of the three C4 grasses and soybean [Glycine max (L.) Merr. ‘Ransom’]. Growth enhancement in response to CO2 enrichment was greater in soybean than in the C4 grasses. By improving their water economy, CO2 enrichment can increase the growth of both C3 and C4 plants under water stress. However, growth stimulation can be expected to be greater in C3 plants.

Weed control strategies for rice (Oryza sativa L.) and soybean [Glycine max (L.) Merr.] emphasize integration of cultural and chemical practices (16, 30, 31). Numerous herbicides are registered and used as preplant, preemergence, or post-emergence applications for control of weeds in rice and soybean (3, 16, 25). Although these herbicide treatments control most of the problem weeds in rice and soybean, most fail to control northern jointvetch [Aeschynomene virginica (L.) B.S.P. # AESVI] in either crop. The two most effective herbicides, 2,4,5-T [2-(2,4,5-trichlorophenoxy) acetic acid] and silvex [2-(2,4,5-trichlorophenoxy) propanoic acid], for control of northern jointvetch in rice have been under the U.S. Environmental Protection Agency's (EPA) Rebuttal Presumption Against Registration (RPAR) process which may ultimately cancel the use of both herbicides in rice (50). New, effective control strategies are needed for control of northern jointvetch in rice and soybean.

Translocation and metabolism of 14C-2,4-D [(2,4-dichlorophenoxy)acetic acid] and effects of 2,4-D on protein synthesis were compared in ‘T–68’ (2,4-D tolerant) and ‘Viking’ (susceptible) birdsfoot trefoil (Lotus corniculatus L.) in an attempt to elucidate some tolerance mechanisms. After 14C-2,4-D was applied to upper trifoliate leaves, significantly less 2,4-D was found in stems, in leaves below the treated leaves, and in roots of T–68 compared to Viking. More 2,4-D was bound to alcohol-insoluble cellular constituents of T–68 leaves, stems, and roots. When alcohol-soluble components were fractionated, slightly more 14C water-soluble compounds were found in T–68, indicating further inactivation by glycosylation. No amino acid-2,4-D conjugates were found. The rate of 14CO2 evolution from 14C-2,4-D treated seedlings in T–68 was five times that in Viking. Protein synthesis appeared to be more rapid in T–68 but the relationship to 2,4-D was not clear. In part, 2,4-D resistance in T–68 may result from its ability to inactivate 2,4-D by differential binding and conjugation and by side chain breakdown as indicated by 14CO2 release.

Collego™ is a selective postemergent mycoherbicide for the control of northern jointvetch [Aeschynomene virginica (L.) B.S.P. # 2 AESVI] in rice (Oryza sativa L.) and soybean [Glycine max (L.) Merr.]. Collego is a two-component product. Component A is a water-soluble spore rehydrating agent while Component B is a water-suspendible dried spore preparation of the fungus Colletotrichum gloesporioides (Penz) Sacc. f. sp. aeschynomene ATCC 20358. Both components are packaged in an 18.9-L plastic mixing container. A mixture containing 0.95 L of Component A and one package of Component B will treat 4 ha. The dried spore component is packaged by number of viable spores rather than by weight. Consequently, the weight of each package will vary from lot to lot, but each package contains a minimum of 75.7 × 1010 viable spores.

Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), and clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were applied to honey mesquite (Prosopis glandulosa Torr. # PRCJG) on seven different dates about every 3 weeks from May to September in 1980 and 1981. Concentrations of 2,4,5-T or triclopyr in stem tissue were usually less than 2 μg/g fresh weight regardless of date of application. Concentrations of picloram and clopyralid were as high as 11 and 22 μg/g fresh weight, respectively, in upper stem phloem at some dates of application. Higher concentrations of all herbicides were detected in upper stem phloem than in the upper stem xylem or basal stem phloem or xylem. More herbicide tended to be detected in stems when herbicides were applied early (May and June) than late (August and September) in the season. Concentrations of triclopyr and picloram recovered from honey mesquite stems were about 25% greater at 3 than at 30 days after treatment, whereas concentrations of 2,4,5-T and clopyralid were about 50% greater at 3 than at 30 days after application.

Field experiments were conducted to determine the effect of nitrogen fertilization on competition between wild oat (Avena fatua L. # AVEFA) and spring wheat (Triticum aestivum ‘Anza’). Nitrogen fertilizer treatments were applied over several wild oat-wheat density combinations. Wheat grain yield in wild oat-infested plots generally declined with fertilization while the density of wild oat panicles increased. Apparently, in competition with wheat, wild oat was better able to utilize the added nitrogen and thus gained a competitive advantage over the wheat. The increased competitiveness of wild oat resulted in reduced crop yields. Under the conditions of these experiments, nitrogen fertilization resulted in positive wheat yield response only when the wild oat plant density was below 1.6 percent of the total plant density.

Ethylene gas stimulated seed germination of the pearl millet [Pennisetum americanum (L.) K. Schum] strain of Striga hermonthica (Del.) Benth. # STRHE) in two soil types in the North Kordofan Region of Sudan. Soils were the noncracking clay pediplain or ‘Gardud’, in Arabic, and the stabilized sand locally called ‘Qoz’. Ethylene at 1.5 kg ai/ha induced greater seed germination (suicidal seed germination) in the Gardud soil than in the Qoz soil. However, ethylene at 3.0 kg ai/ha was better on Qoz than Gardud soil. The effect of injection depth of ethylene was dependent on soil type. Ethylene was more effective when injected at a 15-cm depth in the Gardud soil and at a 30-cm depth in the Qoz soil. The viable population of S. hermonthica seed was reduced by suicidal seed germination at soil depth to 60 cm and to a horizontal distance of 25 cm from the point of ethylene injection. Ethylene-induced germination reduced seed population by 67 and 34% in Gardud and Qoz soils, respectively. A single injection of ethylene diffused up to 300 cm horizontally and up to 60 cm vertically and caused 12.6 and 8.5% reduction in viable 5. hermonthica seed in Gardud and Qoz soils, respectively. The potential of ethylene gas as an effective tool in striga control operations in a pediplain and stabilized sand soil such as is found in N. Kordofan is dependent upon the availability of the gas and the injection apparatus and the economics of its application.

Methyl isothiocyanate (MIT) consistently killed large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] seed at concentations of 4.0 mM or greater. Concentrations of 0.6 to 1.0 mM MIT delayed germination of large crabgrass seed but ultimately allowed the majority of seed to germinate. Dormant large crabgrass seed were killed at concentrations of MIT similar to those required to kill nondormant seed. MIT stimulated germination of dormant large crabgrass seed at sublethal concentrations (0.1 to 1.0 mM). Experiments with metham (sodium methyldithiocarbamate) in the greenhouse and field (metham rapidly degrades to MIT in soils) confirmed results of laboratory experiments with MIT.

Akinetes (spores) of the green, filamentous alga Pithophora oedogonia (Montagne) Wittrock were more copper resistant than filamentous cells, tolerating copper concentrations as high as 4 μg·ml-1 (16 μg·ml-1 copper sulfate pentahydrate). The localization of copper in viable and nonviable cells was conducted using cell fractionation and cytochemical/ultrastructural methods. In copper-exposed viable akinetes, copper was bound primarily to the outer layers of the cell wall. In nonviable cells, copper was found randomly distributed throughout the cytoplasmic and vacuolar regions. No evidence for compartmentation of copper as vacuolar or intranuclear deposits was demonstrated. Copper uptake into the cell wall was associated with release of equimolar amounts of calcium, magnesium, and zinc. When viable copper-treated akinetes were allowed to recover in copper-free medium, the copper was gradually released from the cell wall, presumably to the culture medium. A portion of the copper also appeared to be redistributed to new cell wall material during the akinete germination process. The differential tolerance of P. oedogonia akinetes to copper in comparison to filamentous cells appears to be due to a combination of factors that include cell surface/volume ratios, metabolic activity, and cell wall copper-binding components.

An isolate of Sclerotinia sclerotiorum (Lib.) de Bary collected from a Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] plant in Montana proved pathogenic on Canada thistle in field trials. In addition to attacking the thistle crown and causing wilting and death of the shoots, S. sclerotiorum also infected the root system. The high percentage of thistle shoot kill (20 to 80%) after treatment, and subsequent reduction in plant thistle density the following year, demonstrated the potential of S. sclerotiorum as a biological control agent for Canada thistle in Montana.

Seedling vernalization was more effective than seed vernalization in promoting flowering of downy brome (Bromus tectorum L. # BROTE). Vernalizing imbibed downy brome caryopses at 3 C for 0 to 30 days did not induce rapid flowering when the caryopses were planted. Downy brome seedlings were exposed for 30 days to six photoperiod/temperature treatments. After subsequent transfer to long days, plants from the short-day/3 C treatment flowered within 30 days. Flowering was delayed or was absent in treatments with higher temperatures or long days. The shoot apex increased in volume during the short-day/3 C vernalization period. Two days following vernalization, floral initiation had occurred. By day 5, lateral organs had proliferated. Rudimentary glumes and lemmas were visible by day 8.

Although the problems with waterhyacinth (Eichhornia crassipes [Mart.] Solms; # EICCR) have diminished in the United States over the last decade, the weed continues to be troublesome and requires constant management on a maintenance basis (29, 30). Chemical herbicides are currently the principal means of control when an immediate solution to a waterhyacinth problem is needed. Preventive maintenance programs also rely on chemicals to keep the weed populations at acceptable levels and to prevent weed migration into unwanted areas. However, when control is not urgently required or is economically unfeasible due to the location of the weed, a combination of biological control agents is used. The latter may have been the important factor that contributed to the lessening of the weed problem in this country over the past decade (43).

Hydrilla [Hydrilla verticillata (L.f.) Royle # HYLLI] was grown for 4 to 16 weeks in pans filled with either an organic muck-sand soil, sand, or sand mixed with Osmocote, Esmigran, and dolomite under outdoor conditions in plastic-lined pools with flowing pond water. Dry weight for plants cultured in sand plus the fertilizers was dependent on the concentration of fertilizer and was from 6 to 14 times that of plants cultured in sand alone. Dry weight was also higher for three treatments of sand amended with fertilizer than for plants cultured in the organic muck-sand soil. Water temperature for different growth periods influenced dry weight of hydrilla cultured with all three root media. Tuber production was independent of three levels of fertilizer for 16 weeks of plant growth, but plant weight was dependent on the concentration of nutrients in the root zone. Of nine plant tissue nutrients measured, only phosphorus in both the shoots and roots was dependent on the level of fertilizer in the root zone. This suggests that growth of hydrilla is controlled by nutrients in the root zone. The use of sand amended with various levels of fertilizers may be a way to simulate fertility levels of sediments as a method to study aquatic sites for their potential to support growth of hydrilla.

Seed from 21 common milkweed (Asclepias syriaca L. # ASCSY) populations from six states were germinated on six substrates (filter paper, sand, peat, clay, and mixtures) under three temperature regimes. The variation in germination response between populations and experimental conditions was analyzed. The greatest percent germination (59% average over all substrates) was obtained with an alternating 20 C (16 h), 30 C (8 h) temperature regime. At a constant temperature of 30 C, germination was lower (32% average) and much more variable among seeds from different populations. At 25 C, average percent germination dropped to 1.2% over all substrates. Germination appeared to be strongly correlated with seed source (population), temperature, and substrate type, and poorly correlated with seed size. No association was found between geographical origin and germination response.

Partially purified glutathione-s-transferase (GST) isolated from corn (Zea mays L.) seedlings was about 14-fold higher in specific activity than GST isolated from giant foxtail (Setaria faberi Herrm. # SETFA) seedlings. Greater amounts of GST activity were present in leaf tissue than in stem tissue. Four-leaf giant foxtail seedlings contained about threefold more reduced glutathione per gram fresh weight in the leaves than one- to two-leaf giant foxtail seedlings. When atrazine and reduced glutathione were used as substrates, tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane] inhibited isolated GST from corn with an I50 of about 5 μM and from giant foxtail with an I50 slightly lower. Tridiphane inhibited the metabolism of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] to water-soluble metabolites in giant foxtail leaves but not in corn leaves. Unmetabolized atrazine levels tended to be greater in giant foxtail seedlings treated with tridiphane plus atrazine than in plants treated with atrazine alone. Tridiphane applied 12 h before atrazine increased the uptake of atrazine in both corn and five-leaf giant foxtail seedlings. The amount of atrazine metabolism to water-soluble metabolites increased in corn leaves but remained constant in giant foxtail leaves when atrazine uptake was increased. Tridiphane and atrazine combinations impaired net photosynthetic rates more than atrazine alone in giant foxtail seedlings but did not increase chlorophyll fluorescence. There was no decrease in net photosynthetic rate 12 h following applications of atrazine or tridiphane plus atrazine on corn leaves. Tridiphane did not decrease photosynthesis or increase chlorophyll fluorescence in either species when applied alone.

Occurrence of various growth stages of major pasture plants near Lincoln, NE, were recorded for 15 yr, 1958 to 1973. The phenology of 31 perennial and 16 biennial, winter annual, and annual broadleaf species and 18 grasses was determined. Phenological stages of broadleaf species were recorded as: emergence, stem elongation, first bud, first bloom, and seed firm. Events recorded for the grasses were: emergence, culm elongation, head exserted, anthesis, and seed firm. Much variation existed in phenology among and within life habit groupings of species. Year-to-year variability in phenology of these plants was dependent on temperature patterns of specific years. Studies of this nature are useful in developing more efficient control methods for weeds, insects, and diseases.

The effects of johnsongrass [Sorghum halepense (L.) Pers. # SORHA] infestations were determined during a 2-yr study on sugarcane (Saccharum officinarum L. ‘CP-65-357’) yield. Both cane and sugar yields were lower (36 and 31%, respectively) in plots heavily infested with johnsongrass than in weed-free plots. Sugarcane yields were inversely influenced by johnsongrass equivalents (the sum of the values obtained by multiplying the number of clumps by their corresponding importance value for each plot). In 1983, both johnsongrass standing crop and johnsongrass equivalents correlated negatively with cane yield much better than any other factor combinations, while in 1984, the same was true for stalk population. Substantial yield reductions from johnsongrass interference were observed at johnsongrass infestation levels higher than 15 to 35%.

Phenolic content, germination percentage, and host preference were compared among 11 seed populations of witchweed (Striga hermonthica (Del.) Benth. # STRHE). Significant differences in germination percentage occurred among the seed populations after preconditioning by their exposure to different durations of warm-moist conditions. Greatest percentage of seed germinated after 8 days of preconditioning. Preconditioning for more than 16 days reduced percentage germination. The host specificity range of witchweed seed populations that parasitized pearl millet [Pennisetum americanum (L.) K. Schum] was broader than were those seed populations that attacked sorghum [Sorghum bicolor (L.) Moench.]. Results of thin-layer chromatography indicated large variations in phenolic content among the witchweed seed populations.

Greenhouse-grown kochia [Kochia scoparia (L.) Schrad. # KCHSC] seedlings from populations having either a 13-yr triazine history or no triazine history were sprayed postemergence with 0, 2, or 20 kg/ha atrazine [6-chloro-N-ethyl-N′-[1-methylethyl)-1,3,5-triazine-2,4-diamine]. Fresh weight was reduced 20% in triazine history kochia treated with 20 kg/ha atrazine. Seedlings with no triazine history were killed by 2 kg/ha atrazine. Biotypes resistant to atrazine were also resistant to five other triazine herbicides. Biotypes susceptible to atrazine were susceptible to the other triazines. Atrazine-resistant biotypes were more susceptible to 2,4-D [(2,4-dichlorophenoxy)acetic acid] than atrazine-susceptible biotypes, but atrazine history had no effect on response to diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea].

Shoot and root growth of green foxtail [Setaria viridis (L.) Beauv. # SETVI] and yellow foxtail [Setaria lutescens (L.) Beauv. # SETLU] were compared under three moisture regimes under simulated field conditions in 1982 and 1983. An increase in water supply from 0.3 to 2.5 cm/week resulted in proportionately greater increases in the number of tillers and leaf area of green foxtail compared to yellow foxtail. In 1982, green foxtail produced approximately three times as many seed as yellow foxtail under all three water regimes, whereas under warmer conditions in 1983, green foxtail produced nearly six times as many seed as yellow foxtail under the highest water regime and more than 11 times under the lowest regime. By using a specially constructed periscope to observe root growth through clear plastic tubes implanted in the soil it was determined that the amount of available moisture had much less effect on root growth than on shoot growth of the two species. In 1982, green foxtail tended to produce more roots than yellow foxtail early in the season but as the plants matured no significant differences occurred between species. In 1983, no significant differences in total root length occurred between species at any growth stage. The roots of both species penetrated to a depth of nearly 60 cm, with the highest concentration of roots occurring at depths of 20 to 30 cm.