Field studies were conducted in North Carolina in 1981 and 1982 to evaluate the efficacy of postemergence over-the-top and postemergence-directed herbicides for control of five morningglory species: entireleaf [Ipomoea hederacea (L.) Jacq. var. integriuscula Gray], tall [Ipomoea purpurea (L.) Roth. ♯3 PHBPU], ivyleaf [Ipomoea hederacea (L.) Jacq. var. hederacea ♯IPOHE], pitted [Ipomoea lacunosa (L.) ♯ IPOLA], and scarlet [Ipomoea coccinea (L.) ♯IPOCC]. The glabrous morningglories (scarlet and pitted) were more easily controlled than the pubescent morningglories (ivyleaf, tall, and entireleaf). Lower soybean injury, higher morningglory control, and greater soybean seed yields were obtained with over-the-top herbicide applications at 4 weeks after planting (WAP) than at 6 WAP. Pitted morningglory was tolerant to low rates of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid]. This herbicide applied over the top at the R1 stage of soybean growth produced low yields, probably as a result of morningglory interference and herbicide injury to the soybeans. Postemergence-directed applications of linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and metribuzin [4-amino-6-tert-butyl-3-(methylthio-as-triazin-5(4H)-one] alone or in tank mixtures with 2,4-DB resulted in soybean injury that ranged from 12 to 36%. Highest soybean seed yields (equivalent to weed-free control) from postemergence-directed herbicides were obtained with applications of 2,4-DB, linuron, and a tank mixture of metribuzin and 2,4-DB.

A standard weed management system (system I) had a higher return above variable costs than did an intensive weed management system (system II) for two eastern Colorado cropping rotations. For continuous corn (Zea mays L.), the return above variable costs averaged $18.85/ha more under system I than under system II. For a barley (Hordeum vulgare L.)-corn-sugarbeet (Beta vulgaris L.) rotation, the return above variable costs averaged $20.48/ha more under System I than under System II. Based on alternative input (herbicide) and product prices, higher herbicide costs favored the standard weed management system, whereas higher crop prices favored the weed management system with the higher yields adjusted for quality. The probability that returns above variable costs differed between the two weed management systems depended upon the level of product prices and herbicide costs.

Insensitivity to atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and certain other herbicides was found in plants of horseweed (Conyza canadensis (L.) Crong. ♯4 ERICA) collected from vineyards where atrazine had been applied extensively. There were no differences in the uptake, translocation, or accumulation of radiolabeled atrazine between plants of the susceptible and resistant biotypes. However, atrazine at 1 × 10-4 M caused no inhibition of photosynthetic electron transport in resistant leaves. Photosynthetic characteristics of leaves of susceptible and resistant plants showed different sensitivities to atrazine, but similar sensitivities to diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and ioxynil (4-hydroxy-3,5-diiodobenzonitrile). Isolated chloroplast membranes from resistant plants exhibited a resistance factor of 1000 to atrazine but only 10 to 30 to methylthio-s-triazines. DNOC (4,6-dinitro-o-cresol) was found to be more effective in susceptible chloroplasts than in resistant ones. A marked reduction in the galactolipid content, especially digalactosyl diglyceride, was found in resistant leaves. It is suggested that these alterations in lipid content and composition may contribute to atrazine resistance in horseweed.

Growth chamber studies using one soil investigated the effects of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0.0, 0.4, and 0.8 ppmw on the root development and the mineral status of wheat (Triticum aestivum L. ‘Neepawa’) seedlings. The 0.8-ppmw trifluralin rate increased the number of seminal roots, reduced lateral root production, decreased root extension, caused root tips to swell (club-like appearance), and reduced root dry weights. However, 0.4-ppmw trifluralin caused only slight damage to the seedlings. Towards the end of the two-week growth period, damaged seedlings showed signs of recovery, which included an increased number of seminal roots, development of normal root extensions from clubbed root tips, and development of normal lateral root patterns. Trifluralin increased percent calcium and magnesium and decreased percent nitrogen, phosphorus, and potassium in wheat plants. The nutrient concentrations were more affected in 21-day-old plants than in 35-day-old plants, indicating the wheat seedlings were able to recover from trifluralin injury.

Bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifway’] injured by MSMA (monosodium methanearsonate) plus metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] or 2,4-D [(2,4-dichlorophenoxy)acetic acid] plus mecoprop {2-[(4-chloro-o-tolyl)oxy] propionic acid} plus dicamba (3,6-dichloro-o-anisic acid) recovered more rapidly when nitrogen (N) was applied in sequence with the herbicides than when no N was applied. Bermudagrass recovery was faster with less injury within 2 weeks after herbicide treatment when N was applied at the first MSMA plus metribuzin treatment or when N was applied at 2 weeks after the first 2,4-D plus mecoprop plus dicamba treatment. Turf quality at 4 weeks or later was consistently as good or better in plots where N was applied at 2 weeks after the first application of either herbicide combination than when N was applied earlier.

Field studies were conducted to evaluate the effect of quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE] density and soil moisture on corn (Zea mays L.) growth and yield. Quackgrass densities ranging from 65 to 390 shoots/m2 reduced corn yield 12 to 16%. A quackgrass density of 745 shoots/m2 reduced corn yields an average of 37% and significantly reduced corn height, ear length, ear-fill length, kernels/row, rows/ear, and seed weight. In the soil moisture study, quackgrass was shorter than corn throughout the growing season, and analyses of corn leaf tissue indicated that quackgrass did not interfere with the nutrient status of the corn. In 1979, soil moisture was not limiting and corn yields were similar in all treatments regardless of irrigation or the presence of quackgrass. In 1980, soil moisture was limited and irrigation increased the yield of quackgrass-free corn. Irrigation also increased the yield of quackgrass-infested corn to a level similar to irrigated corn. When light and nutrients are not limiting factors, an adequate supply of soil moisture can eliminate the effects of quackgrass interference on the growth, development, and yield of corn.

Four cultivations of cotton [Gossypium hirsutum L. ‘Stoneville 213′] alone failed to reduce green weed biomass or increase seed cotton yields above that of the no weed control treatment, and thus resulted in a negative net return (−200 to −450 $/ha) all 4 yr. Two cultivations plus two hand-hoeings reduced green weed biomass and increased seed cotton yields 3 out of 4 yr, thus a positive net return was produced for 3 yr ranging from 300 to 640 $/ha. Fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] alone was the most effective treatment in reducing green weed biomass and increasing seed cotton yields, and produced the highest net return, 280 to 420 $/ha for the 4-yr period. The addition of cultivation did not improve the fluometuron treatment. However, diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea)] required three supplementary cultivations to equal the single fluometuron treatment. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) plus three cultivations did not equal the single fluometuron treatment, although a positive net return was obtained every year. The addition of trifluralin to fluometuron also failed to improve weed control or net return over that of fluometuron alone.

Velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH) and Powell amaranth (Amaranthus powellii S. Wats. ♯ AMAPO) control with pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] was dependent on proper timing of application. Preemergence and early postemergence pendimethalin treatments provided effective control, but control rapidly diminished with later postemergence treatments, particularly on Powell amaranth. Time-course studies on the effects of pendimethalin on the growth of these species indicated that pendimethalin inhibited shoot growth by slowing or stopping the production of leaves and branches, as well as reducing leaf size and internode length. Pendimethalin appeared to have its greatest effect on portions of the shoot undergoing cell division.

An assessment was made of various parameters to measure growth of soybean [Glycine max (L.) Merr. ‘Wilkin’] and einkorn (Triticum monococcum L.) cell suspension cultures to establish convenient methods of screening the effects of chemicals. Methods assessed were settled cell volumes, packed cell volumes, absorbance at 525 nm of sonicated aliquots, dry weights (of aliquots or entire flask contents), and electrical conductivity and pH of the culture medium. Settled cell volumes, conductivity, and dry-weight changes were the most useful of the methods tested for determining the phytotoxicity of a nonionic linear alcohol ethylene oxide detergent (an adduct of 1-dodecanol containing eight ethylene oxide units) and the methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Because 3 to 4 weeks were required to assess whether the cultures could grow out of the initial inhibition by the detergent or herbicide, none of the methods was rapid. Advantages and disadvantages of the various methods and their relative values for screening compounds are described.

Fluazifop-butyl {(±) butyl 2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, haloxyfop-methyl {methyl-2-[4-[[3-chloro-5-(trifluoromethyl-2-pyridinyl] oxy] phenoxy] propanoic acid}, and sethoxydim {2-[1-(ethoxyimino)-butyl]-5-[2-ethylthio)propyl-3-hydroxy-2-cyclohexen-1-one}exhibited soil herbicidal activity to annual grass species in greenhouse and field experiments. Control of forage sorghum [Sorghum bicolor (L.) Moench. ‘Rox Orange’] with all three herbicides was greater when seeds were planted at or near the soil surface than when planted 2, 4, or 6 cm deep. Imbibition of the herbicides by forage sorghum and soybean [Glycine max (L.) Merr.] seeds did not reduce germination at concentrations of 10-3 M or lower, but forage sorghum seedling survival and vigor were reduced by herbicide concentrations as low as 10-7 M. Fluazifop-butyl, haloxyfop-methyl, and sethoxydim were more phytotoxic when applied to the root zone than the shoot zone. Haloxyfop-methyl exhibited the longest soil residual control in the field followed by fluazifop-butyl and sethoxydim. Haloxyfop-methyl and fluazifop-butyl controlled simulated shattercane [Sorghum bicolor (L.) Moench. ♯3 SORVU] in soybeans with preemergence and early postemergence applications, whereas control from similar applications of sethoxydim was limited and variable.

The C4 weed johnsongrass [Sorghum halepense (L.) Pers. ♯3 SORHA] and the C3 crop soybean [Glycine max (L.) Merr. ‘Ransom’] were grown separately and in inter- and intraspecific competition at 350 and 675 ppm CO2 in controlled environment chambers with 29/23 C day/night temperatures and 950 μE·m-2 · s-1 PPFD (photosynthetic photon flux density). In the absence of competition, the higher CO2 concentration stimulated dry matter accumulation, leaf area expansion, net assimilation rate, and leaf area duration of soybean more than that of johnsongrass. The plant relative yield (PRY) of soybean in competition with johnsongrass increased, and the PRY of johnsongrass in competition with soybean decreased, as the CO2 concentration was increased from 350 to 675 ppm. Thus, the competitiveness of the C3 crop with the C4 weed increased with increasing CO2 concentration. Relative yield totals were not significantly different from 1.0, indicating that the two species were competing for the same resources. With the increases in global atmospheric CO2 concentration predicted for the next 50 to 100 yr, the competitiveness of C3 crops with C4 weeds could be increased.

The formulation of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) encapsulated within a starch granule can reduce the loss in activity associated with the delayed incorporation of the emulsifiable concentrate formulation of trifluralin. Good weed control and high soybean [Glycine max (L.) Merr. ‘Wells II’] yields were obtained when a starch formulation of trifluralin was applied in the fall and incorporated at planting time the following spring. The cultural practices of shallow incorporation, delayed incorporation, and/or midseason cultivation intensified the weed control provided by a starch formulation of trifluralin. The adsorption of additional trifluralin onto the granule surface, cross-linking starch xanthate with a weak oxidant, and mixing granules with different release rates also increased initial control. Granules produced by the starch-calcium and starch-borate processes exhibited many of the same characteristics of granules produced by the older starch xanthate process, but are much less expensive to produce and do not require the use of the toxic carbon disulfide in the encapsulation process. The combination of an appropriate starch formulation of trifluralin with proper cultural practices provided good weed control from fall and spring applications of trifluralin.

Five presumed biotypes were identified among field bindweed (Convolvulus arvensis L. ♯3 CONAR) clones collected from a field population near Lafayette, IN. Consistent variations in leaf morphology, floral characteristics, and accumulation of shoot and root biomass were found between biotypes when grown in a controlled environment. The biotypes also differed in their flowering capacity. The earliest flowering biotype formed flowers 23 days before the latest and produced 19 times more flowers per plant, which indicated further differences in seed production potential between biotypes. Pollination studies helped to differentiate biotypes within the population and showed that the presumed biotypes were self-incompatible. Vegetative reproduction potential of the biotypes varied from 1.8 to 74.5% in the number of root buds that developed into shoots. The variability in growth and reproduction observed between these field bindweed biotypes may explain the survival and adaptability of a population of this weed as environmental conditions and control practices change.

The applicability of fluorescence measurements for the detection of herbicide effects in whole leaves was analyzed. Based on the results known for isolated chloroplasts, normalized variable fluorescence of the initial rise was shown to be an appropriate tool for monitoring effects of photosystem II (PS II) herbicides. Equipment is described for monitoring the degree of inhibition by fluorescence induction measurements and microcomputer data analysis. The method is used to study the effect of pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone], BAY DRW 1139 [4-amino-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one], and phenmedipham {3-[(methoxycarbonyl)amino] phenyl (3-methyl-phenyl)carbamate} after foliar application to different species. A rapid decrease of normalized variable fluorescence indicates penetration into leaf cells of all species tested. During a 5- to 7-day experiment, the apparent variable fluorescence decreased continuously in herbicide-susceptible plants, while it recovered in resistant plants due to an internal detoxification mechanism. The described method provides a rapid, simple, and nondestructive tool for analyzing the kinetics of penetration and detoxification of PS II herbicides in whole leaves.

The effects of mineral element uptake on the growth and development of the aquatic plant hydrilla [Hydrilla verticillata (L.f.) Royle.] were studied in a short-term experiment under laboratory conditions. On a dry-weight basis, maximum growth of hydrilla plants was obtained at a 0.016 ppm P and 5 ppm Ca in the growing media. Hydrilla responded favorably to high concentrations of K (40 ppm in the growing media). The presence of 2,4-dinitrophenol (2,4-DNP) reduced uptake of K, Cu, Fe, Mn and did not significantly affect the uptake of Ca or P. Thus the uptake of K, Cu, Fe, and Mn by hydrilla appears to be dependent on metabolic energy.

Scarification in sulfuric acid consistently increased germination of Opuntia edwardsii sp. nov, O. discata Griffiths, and O. lindheimeri Engelm. ♯ OPULI seeds over that of untreated seeds. Optimum constant temperatures for germination were generally 25 to 35 C and germination was not enhanced by alternating temperatures. There was a trend for increased germination following leaching in water for 12 h which suggested the presence of chemical germination inhibitors. Seeds passed through the digestive tracts of cattle exhibited average germination percentages that were 1.5 times greater than seeds removed from ripe fruits.

Two species of annual nightshades were commonly found as agronomic weeds in Minnesota. Eastern black nightshade (Solanum ptycanthum Dun.), the most common species, was found throughout the southern half of the state. Hairy nightshade (Solanum sarrachoides Sendt. ♯3 SOLSA) was found only in a few scattered locations. Eastern black nightshade seedling emergence began in mid-April or early May, and more than 80% of the total yearly emergence occurred before June. Hairy nightshade emergence began in May, but less than 70% of its total yearly emergence occurred before June. Eastern black nightshade berries first contained viable seeds 4 to 5 weeks after flowering of the plants and a week or more before the berries began to turn black. Hairy nightshade generally required a week longer than eastern black nightshade for viable seed production after flowering.

The susceptibility of sweet pepper (Capsicum annuum L. ‘Keystone Resistant Giant’) and tolerance of hot pepper (Capsicum chinense L. ‘Bohemian Chili’) to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was demonstrated under greenhouse and field conditions. Sweet pepper growth and fruit production were inhibited by foliar applications of bentazon at rates of 0.6 to 6.7 kg ai/ha. Severity of injury increased with application rate. Injury symptoms in sweet pepper were leaf chlorosis, with necrosis and death of shoot apices. Foliar applications of bentazon to hot pepper resulted in little or no injury. Bentazon inhibited Hill reaction activity of isolated chloroplasts from both species to a similar extent, suggesting that selectivity of this compound in hot pepper is not due to resistance at the chloroplast level.

Correlations between herbicide damage and several physiological factors were examined in the field for ponderosa pine (Pinus ponderosa Dougl. ex P&C Lawson) and greenleaf manzanita (Arctostaphylos patula Greene). Pine injury caused by 2,4-D [(2,4-dichlorophenoxy) acetic acid], glyphosate [N-(phosphonomethyl) glycine], or triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid]} was compared to leader growth rate, needle growth rate, predawn xylem potential, daytime xylem potential, and photo synthetic rate occurring on the dates of herbicide application. Shrub injury for each of the three herbicides was compared to predawn xylem potential, daytime xylem potential, and photo synthetic rates. Both species exhibited less injury from herbicide applications made at the end of September than from any applications made from April through October. Comparison of factors highly correlated to herbicide damage indicates that highest herbicide selectivity occurs when pine has ceased growing, the xylem potential of the pine is relatively low (high water stress), and the xylem potential of the manzanita is relatively high.

Mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide}+bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] at 0.14 + 0.84 kg ai/ha was the most injurious of five herbicide treatments applied once to one- to two-leaf red rice (Oryza sativa L. ♯3 ORYSA). The most injurious treatment to five-to six-leaf red rice was DPX Y6202 {ethyl [2-[4-[6-chloro-2-quinoxalinyl]oxy]phenoxy] propionate} at 0.56 kg ai/ha. Two applications, regardless of red rice growth stage, of all treatments except fluazifop {[±]-butyl-2-[4-[[5-trifluoromethyl]-2-pyridinyl] oxy] phenoxy] propanoate} resulted in 86 to 99% injury.