Rates of 0 and 5 lb/A of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) or 2-chloro-4,6-bis(ethylamino)–s-triazine (simazine) were combined with O and 200 lb/A of nitrogen fertilizer as preemergence applications on plots planted to corn (Zea mays L., var. Mo. 880) in May of 1964 and 1965. Soil samples collected in December, 1965, and again in February, 1966, were plated on Difco potato dextrose agar and nutrient agar to determine the growth of fungal and bacterial colonies. There was no difference in the total number of fungal colonies grown on media seeded with soils from the field studies, yet variation in individual species occurred. The number of bacterial colonies increased on plates seeded with soil from plots treated with 200 lb/A of nitrogen plus 5 lb/A of simazine but not from simazine-treated soil without nitrogen.

Nitrate reductase activity of seed leaves and the first three true leaves of tall morningglory [Ipomoea purpurea (L.) Roth] was shown to increase rapidly initially then gradually decrease. The greatest level of reductase activity of each true leaf was reached at the fourth to fifth day after unfolding. A subsequent leveling off of enzyme activity corresponded to the acceleration of leaf growth. Leaf nitrates were correlated with enzyme activity. The sum of leaf activities was used to estimate the total reductive capacity of the plant leaf tissue at each sampling date.

A culture medium and environmental conditions were selected for ovule culture of velvetleaf (Abutilon theophrasti Medic. ♯4 ABUTH), which allowed development parallel to that occurring in vivo. Of the six nutrient media evaluated, the most suitable one contained an organic nitrogen source and was of high osmotic potential. A liquid medium with a pH of 5 to 7, and culture for 14 days at 25 C under green light (1.3 μmole·m-2·-1) encouraged good embryo and ovule development. No difference was recorded between polyethylene glycol 20000 and mannitol in the medium used for dehydration and subsequent imbibition of cultured mature ovules. To investigate the effects of maternal tissues, surgical alterations were performed on the testa and funiculus of immature velvetleaf ovules. The intact testa appears to be a barrier to nutrient absorption and reduces the fresh and dry weights and embryo length. Ovule and embryo development was significantly better if either the testa was nicked or the funiculus removed.

Samples of the spray pattern delivered by a tractormounted field sprayer were intercepted with 10 petri dishes divided between two heights in each of eight plots sprayed with 1.12 kg/ha of 4-amino-3,5,6-trichloropicolinic acid (picloram). The sprayer produced predictable residues on the intercept plates; no differences occurred between residues collected at ground level and 46 cm above the ground; and no differences occurred between replicate plots. Fractionation and analysis of specific plant parts, whose position relative to direction of spray and surrounding brush had been noted, revealed that the spray system delivered uniform coverage almost regardless of brush orientation.

Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide]-binding in excised root segments of corn (Zea mays L. ‘NC + 59′) was confined to cell wall fractions (residue and 500 g pellet) remaining after homogenization and to components of the 100 000 g supernatant. Binding increased in both the cell wall and soluble fractions with continued exposure to napropamide. Microautoradiographs revealed that the napropamide bound in the cell walls was located in epidermal, cortical, and stelar tissue. Various proteins were capable of binding napropamide in vitro; however, protease treatment did not liberate the radioactivity bound in the cell wall fragments. Carbohydrate release from the cell wall material with cellulase was not correlated with the solubilization of bound radioactivity and wall carbohydrate monomers did not appear to bind to napropamide in vitro. A portion of the radioactivity found in the soluble components (at 100 000 g) was associated with a molecule of MW > 600. The continued influx of napropamide was due to binding to cell wall components and molecules within the cell.

Tolerance of barley to chlorsulfuron at various stages of crop development was studied in weed-free field and pot experiments. Five barley crops were sown between mid-May and mid-July in the field in 1988 and sprayed simultaneously with four rates of chlorsulfuron when the corresponding stages of crop development ranged from growth stage 7 (GS 7) to GS 31. Early-sown barley yielded more than late-sown barley, but percent grain yield reduction from chlorsulfuron was similar for all planting dates. In a field experiment in 1989, barley was sown at three dates (May, June, and July) and each was treated with chlorsulfuron at 0, 15, 30, and 60 g ai ha−1 at either GS 12 or GS 15. Grain yield of barley sown in May and treated with 15 g ha−1 chlorsulfuron at GS 12 was reduced 35%, compared with no effect when applied at GS 15; this yield reduction was related to spike size and number. Application of chlorsulfuron at GS 12 and GS 15 to barley sown in June caused yield reductions of 20 and 11%, respectively. In contrast, barley sown in mid-July was not affected by chlorsulfuron. Applications of chlorsulfuron at GS 12,13,14, and 15 led to reductions of 75,35,15, and 5% shoot dry matter (DM) of plants grown in pots and measured at GS 33. Root DM was more sensitive to chlorsulfuron than shoot DM. Tolerance of barley to chlorsulfuron increased with age of the plant at the time of application.

Photosynthesis decreased 32% in quackgrass infected with rust. Photoassimilate transport in rust-infected quackgrass, assessed by autoradiography, was less than that of control (no rust) leaves 35 min after exposure to 14CO2. Greenhouse-grown quackgrass height, foliar and rhizome dry weights, rhizome length, and bud numbers decreased 11, 25, 28, 19, and 21% in rust-infected plants, respectively, compared to control plants. Foliar and rhizome biomass decreased 31 and 39%, respectively, in field-grown rust-infected plants. Rhizome bud death 48 h after treatment (HAT) in both control and rust-infected plants increased as glyphosate rate increased from 0.13 to 1 kg ae ha−1; however, control plant bud death was significantly greater than that of rust-infected plants.

A spray chamber was constructed to spray herbicides or growth regulators on small potted plants. Syphon-type pneumatic atomizing nozzles were used to eliminate the need to pressurize the spray solution. Two stationary overhead nozzles deliver the solution to plants rotating on a turntable. The chamber permits convenient and accurate regulation of volume and rate of chemical application for laboratory and greenhouse investigations.

Height, true-leaf area, shoot dry weight, and survival of the seedlings of four varieties of cucumber (Cucumis sativus L.) were measured for differences occurring when treated preemergence with naptalam (N-1-naphthylphthalamic acid) alone, chloramben (3-amino-2,5-dichlorobenzoic acid) methyl ester alone, or with combinations of these two herbicides. These factors were reduced, depending upon the variety of cucumber, with each of the herbicide treatments. The only reduction associated with naptalam alone was the true-leaf area of ‘Model’ and ‘Wisconsin SMR 58.’ ‘Ohio MR 17,’ ‘Model,’ and ‘Wisconsin SMR 58’ had less reduction of all measured responses than ‘Pixie’ when treated with chloramben methyl ester alone or with combinations of naptalam and chloramben methyl ester. The herbicide variety interactions present in seedling injury under greenhouse conditions were not reflected in the yields of these varieties when grown in the field. The only significant yield reduction occurring under field conditions was with the 4.48 kg/ha rate of chloramben methyl ester in the first harvest.

The reduction and assimilation of nitrate ions by 14-day old tall morningglory [Ipomoea purpurea (L.) Roth] seedlings were studied by monitoring the leaf nitrate, protein, and activity of the enzyme nitrate reductase (NADH: nitrate oxidoreductase, EC 1.6.6.1). The pH's of the grinding and assay mixtures yielding maximum nitrate reductase activity were determined to be 8.8 and 7.5 to 7.7, respectively. The maximum assay time for a linear reaction rate for nitrate reductase was estimated at 10 minutes. Decay rates of the enzyme preparations indicated a half-life of 30 min. Requirements for a cofactor to support the reaction were met with the addition of NADH (1 × 10−3 M final concentration) to the assay mixture. NADPH was not effective in supporting nitrate reductase activity. Inclusion of cysteine (1 × 10−2 M) in the grinding medium was necessary to insure maximum activity of the enzyme preparations. Both light and nitrate were required for nitrate reductase activity in morningglory leaves. Nitrate accumulated in leaf tissue in proportion to the concentration of nitrate in the nutrient medium. Above 7,530 lux luminescence, enzyme activity and tissue protein were related to the light intensity and the availability of nitrate in the nutrient medium on which the plants were grown.

Two yr of field research were conducted to evaluate the efficacy of BAS-9021 {2-[1-(N-allyloxyamino)butylidene]-5,5-dimethyl-4-methoxycarbonylcyclohexane-1,3-dione, Na salt}, HOE 29152 {methyl 2-[4-(4-trifluoromethylphenoxy)phenoxy]propanoate}, and mefluidide N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide as selective herbicides applied postemergence to johnsongrass [Sorghum halepense (L.) Pers.]. All three herbicides afforded 85% or greater control of rhizome johnsongrass in one experiment in 1977, where repeat applications were made and ideal growing conditions prevailed. HOE 29152 also afforded excellent control with a single application made at the boot stage of johnsongrass. In a second experiment in 1977, when drought conditions prevailed, HOE 29152 was the only herbicide that afforded 70% or greater control of the johnsongrass. Both BAS-9021 and mefluidide afforded less than 60% control of johnsongrass in the single 1978 experiment, when evaluated at the end of the season. This study also was subject to drought conditions throughout the growing season.

The carbon banding technique was evaluated for control of volunteer Kentucky bluegrass (Poa pratensis L.) while Kentucky bluegrass was established for seed production. At Madras, Oregon, where terbacil (3-tert-butyl-5-chloro-6-methyluracil), diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], and simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] were applied at several rates each, volunteer Kentucky bluegrass control between the carbon bands ranged from 80 to 99+%. At Corvallis, Oregon, where Colonial bentgrass (Agrostis tenuis Sibth. ‘Highland’), red fescue (Festuca rubra L. ‘Pennlawn’), perennial ryegrass (Lolium perenne L. ‘NK-100’), and orchardgrass (Dactylis glomerata L. ‘S-143’) were planted to allow identification of volunteer Kentucky bluegrass both between and in the carbon bands, diuron, atrazine, and a combination of diuron and terbacil eliminated volunteer Kentucky bluegrass. Terbacil did not control all Kentucky bluegrass between the bands. None of the herbicide treatments adversely affected crop establishment or seed yield.

The herbicide 2,4,5-T [(2,4,5-trichlorophenoxy) acetic acid], at concentrations of 10−4 and 10−6 M in nutrient media, was more inhibitory to the growth of soybean (Glycine max (L.) Merr. “Acme”) tissue culture than dicamba (3,6-dichloro-o-anisic acid) or picloram (4-amino-3,5,6-trichloropicolinic acid). Dicamba (10−6 and 10−8 M) and 2,4,5-T (10−8M) stimulated growth of soybean tissue. Mixing equimolar solutions of 2,4,5-T + dicamba, 2,4,5-T + picloram, or picloram + dicamba at 10−4, 10−6, and 10−8 M did not increase phytotoxicity over that of the most phytotoxic herbicide of the pair.

Field experiments were conducted to study the feasibility of applying glyphosate [N-(phosphonomethyl) glycine] postemergence with a recirculating sprayer and a vertical roller for the control of common lambsquarters (Chenopodium album L.), common sunflower (Helianthus annuus L.), kochia [Kochia scoparia (L.) Schrad.], redroot pigweed (Amaranthus retroflexus L.), and velvetleaf (Abutilon theophrasti Medic.) in sugarbeets (Beta vulgaris L.). Glyphosate was applied twice each year at 1.7 kg/ha with a recirculating sprayer in 1977 and 1978, or twice as a 20% (v/v) solution with a vertical-roller applicator in 1979. By harvest, 70 to 74% of the total population of treated common sunflower, kochia, and redroot pigweed, 61% of the common lambsquarters, and 30% of the velvetleaf was dead. Root yields in glyphosate-treated plots, when averaged over 3 yr, were increased 5800, 8500, 12 500, and 13400 kg/ha at densities of 6, 12, 18, and 24 broadleaf weeds (equal densities of common lambsquarters, kochia, and redroot pigweed)/30m of row, respectively. Where equal densities of common sunflower and velvetleaf competed with sugarbeets, root yields in glyphosate-treated plots, when averaged over 2 yr, were increased 4400, 11900, 11700, and 10700 kg/ha, respectively, at these same densities.

The effect of 2,3,5-trichloro-4-pyridinol (pyriclor), as well as carbonyl cyanide m-chlorophenyl hydrazone, 2,4-dinitrophenol, and oligomycin, on oxygen uptake and oxidative phosphorylation was investigated with mitochondria isolated from hypocotyls of etiolated soybeans (Glycine max Merrill, var. Lee). Pyriclor inhibited both coupled and uncoupled reactions. This suggests that pyriclor either acts on a nonphosphorylating intermediate close to the electron carrier chain or with a component of the electron carrier chain, or both.

A new strain of the fungus Plectosporium tabacinum was isolated from naturally-infected false cleavers plants and evaluated as a bioherbicide for the control of both herbicide-resistant and herbicide-susceptible false cleavers in canola. Plectosporium tabacinum was nonpathogenic to both Argentine canola and Polish canola and to both herbicide-tolerant and conventional cultivars. Plectosporium tabacinum killed false cleavers seedlings when applied at a concentration of 1 × 107 conidia ml−1 and provided with 16 h dew. The efficacy of P. tabacinum on herbicide-resistant false cleavers was identical to that on herbicide-susceptible false cleavers. Catchweed bedstraw was also highly susceptible to P. tabacinum. Further host-range tests on 34 plant species in 26 genera and 12 families demonstrated that P. tabacinum is sufficiently host specific for false cleavers control in western Canada. This fungus may provide a novel approach for managing herbicide-resistant false cleavers.

Genome sequences and genome-wide transcript profiles are becoming increasingly available, opening a way to use this information in analyzing how groups of genes are connected in pathways or “regulons” that might explain how organisms accomplish the integration on an organismal level. We have begun to explore the large datasets that are available for transcripts of the best characterized plant model, Arabidopsis thaliana, setting up a gene network using clustering methods. A network, based on the Graphical Gaussian Model (GGM), describes coregulation of genes under a variety of external factors: abiotic, biotic, and chemical treatments. In its present structure, the network reveals coregulation for more than 7,000 genes in the Arabidopsis genome. The network appears to be particularly suited to reveal the regulatory structure of biochemical pathways and environmental stress responses. Examples describe network predictions centered on a trehalose-6-phosphate phosphatase, an Arabidopsis response regulator and EPSPS. Results from the statistical analysis and bioinformatics of large data sets provide hypotheses that must be checked by additional studies. However, networks, which should be expanded from transcripts to also include proteins and metabolites, can be expected to explain not only how the Arabidopsis gene network is structured, but also provide insight in how similar networks in weed species might deviate or show correspondence and overlap.

Jointed goatgrass is an exotic species introduced into the western United States from Eurasia. The weed is an agricultural pest infesting winter wheat fields and causing economic loss. Common ancestry between the two species enables interspecific hybridization, thus providing a mechanism for gene flow to occur. This can facilitate the accumulation of novel genes, which could increase the wild species' competitiveness with wheat and its ability to invade novel habitats. Interest in the development of transgenic wheat cultivars has increased the concern for interspecific gene flow. Gene introgression requires recurrent backcrossing to the weedy species after the initial hybridization event. Field experiments were conducted at two locations in Colorado in 2007–2008 and 2008–2009, with jointed goatgrass acting as the sole source of viable pollen for fertilization of transplanted hybrid plants. Backcrossing rates were determined by conducting germination studies on spikes collected from a total of 206 hybrid plants. Pollination by jointed goatgrass led to the production of 463 BC1 plants from seed produced on these 206 hybrid plants. Ninety-five percent confidence intervals estimate the rate of backcrossing at 0.028 to 0.306% and 0.077 to 0.604%, with medians of 0.062 and 0.152%, respectively, at the two locations. The results demonstrate that backcrossing to jointed goatgrass can occur, despite low rates of hybrid fertility. Subsequent backcrossing would make it likely that a wheat gene conferring a selective advantage will introgress into the weedy population. For the U.S. Great Plains, it is possible that transgenic wheat cultivars will be released in the future and determining proper management of these cultivars is necessary to minimize hybridization and advantageous gene introgression into weedy relatives.

Broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash # BRAPP has recently become the dominant annual grass in certain fields of the North Carolina Coastal Plains. Previously, fall panicum (Panicum dichotomiflorum Michx. # PANDI) and large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] were the dominant annual grasses in the region. One of the possible reasons for the observed population shift could be production of inhibitors or stimulators by one species that affects the population dynamics of the other species. Studies were initiated to evaluate the effects of broadleaf signalgrass, large crabgrass, and fall panicum residue, applied as a mulch or soil incorporated, on five indicator species: the three weeds themselves, corn (Zea mays L.), and soybean [Glycine max (L.) Merr.]. At expected residue levels, the degree of inhibition or stimulation from fall panicum and broadleaf signalgrass was determined to be significant for some indicator species. When such responses were seen, the amount of residue necessary to produce these results was usually within the concentrations normally observed in field situations. Based on these results, it appears that the observed population shift is partially mediated by the production of inhibitors or stimulators through plant residue. Other factors such as differential herbicide selectivity and crop rotation are being investigated.