In field studies, surfactant and phytobland oil were compared as additives to herbicides and herbicide combinations for postemergence weed control in cotton (Gossypium hirsutum L. ‘Stoneville 7A’). Addition of phytobland oil to MSMA (monosodium methanearsonate) and MSMA + fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], dinoseb (2-sec-butyl-4,6-dinitrophenol), or norea [3-(hexadydro-4,7-methanoindan-5-yl)-1,1-dimethyl-urea] had no significant effect on weed control when applied as directed treatments to weeds in cotton 7 to 15 cm tall. In cotton 15 to 23 cm tall, addition of phytobland oil to MSMA + linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and MSMA + linuron + prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] increased weed control when compared to the same treatments with surfactant. MSMA + linuron + phytobland oil decreased cotton yields. Addition of phytobland oil to DSMA (disodium methanearsonate) and DSMA combinations had no effect on weed control when compared to the same treatments with surfactant. There were no differences in several paraffinic phytobland oils or surfactant when used as additives to MSMA + fluometuron for weed control in cotton 7 to 15 cm tall.

The relative susceptibility of ‘Alaska’ and ‘Perfection’ cultivars of peas (Pisum sativum L.) to trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) was studied in excised roots, and in greenhouse and field plantings. Elongation of excised Alaska and Perfection pea roots was reduced 32 and 25%, respectively, by 4 mg/L dosages of trifluralin in aseptic culture, and 25 and 10% by 1.68 kg/ha dosages in greenhouse-grown plants. Seedling emergence in the greenhouse and field was reduced or delayed in both cultivars by 1.68 kg/ha trifluralin. Yields of field-grown Alaska and Perfection peas were reduced by trifluralin dosages equal to and exceeding 0.84 and 1.68 kg/ha, respectively, when there was a June water deficit (8 cm). Yields were not reduced in either cultivar when June rainfall was near normal (10.9 cm).

The uptake and distribution of 14C-bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate] was different among corn (Zea mays L.), soybean (Glycine max (L.) Merr.) and velvetleaf (Abutilon theophrasti Medic.) following preemergence application to a greenhouse soil mix. Autoradiographs of seedlings harvested 14 days after treatment, showed the 14C to be in (or on) those areas of the crop plant in contact with the treated soil. Velvetleaf translocated 14C residue throughout the shoot. Absorption of 14C-compound(s) from treated nutrient solution accumulated in the roots of the three species but to a greater extent in soybean. There was no difference in the concentration of 14C in the shoots. However, in corn and soybean the 14C-compound(s) was confined to the primary and secondary leaf veins while velvetleaf showed a general distribution throughout the leaf tissue. Velvetleaf absorbed and translocated bifenox from shoot zones to a greater extent than the crop plants. Some acropetal movement was noted following leaf application to corn and velvetleaf but movement was only 3% of applied 14C from the treated leaf. No movement was detected in soybean.

Soil-incorporated treatments of dichlobenil (2,6-dichlorobenzonitrile) at 4.5 or 9 kg/ha completely controlled field horsetail (Equisetum arvense L.) for 2 yr and at 9 kg/ha, control was 90 to 99% in the third year. Mulching with sawdust after surface application of dichlobenil gave similar results. In an area treated at 9 kg/ha and isolated from emerged field horsetail, there was no reappearance of field horsetail until 5.5 yr after treatment. Japanese holly (Ilex crenata Thunb.) and azalea (Rhododendron X ‘Rosebud’) planted a year after treatment made as much growth in treated as in adjacent untreated soil. Douglas fir seedlings [Pseudotsuga menziesii (Mirb.) Franco] made as much growth in treated as in untreated soil only when planted 2 yr after treatment. Strawberry (Fragaria X ‘Northwest’) plants made approximately 80% as much top growth in treated as in untreated soil when planted 2 yr after herbicide application.

A field study was conducted with fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 1× and 2× rates in soybeans [Glycine max (L.) Merr.] for 2 consecutive yr to evaluate their persistence in soil and to determine their residual effect on rice (Oryza sativa L.). In another field study that was conducted to evaluate the effect of winter flooding on the persistence of 4× rates of the same herbicides, gas chromatographic analysis and bioassay procedures both revealed increased dissipation of these herbicides because of winter flooding. Flooding rice for 2 or 4 months during winter reduced the adverse effect from herbicidal residues. Laboratory studies evaluated the persistence and volatility of these herbicides at 4 and 25 C in two soils at three moisture contents (air-dried, field capacity, and flooded). The persistence of the three herbicides was similar in the field and in the laboratory and usually followed the order fluchloralin > profluralin = trifluralin. Volatility was most rapid with moisture at field capacity, but overall dissipation was most rapid in flooded soil. Significant dissipation and volatility losses of all three herbicides occurred at 4 C in flooded soil and in soil at field capacity. These studies indicated that winter flooding is effective in reducing the concentration of dinitroaniline herbicides in soil.

Native Polyacrylamide gel electrophoresis (PAGE) and enzyme activity staining were used to identify possible progenitor species of velvetleaf (Abutilon theophrasti Medic. # ABUTH). Multiple forms of superoxide dismutase activity were observed in each of the plants surveyed. Three enzyme forms were common to all the species and bio types while one form was different in the velvetleaf biotypes compared to the other species. Multiple forms of peroxidase activity were also detected. The three velvetleaf biotypes possessed identical enzyme forms with minimal similarity to peroxidase forms found in the other species. Multiple forms of esterase activity separated as two nonoverlapping groups. A slowly migrating group was observed in all the velvetleaf biotypes and a more rapidly migrating group characterized the remaining Abutilon species. The results of this study indicated that the progenitors of velvetleaf were not among the species surveyed and suggested that the progenitors may no longer be extant.

MH (1,2-dihydro-3,6-pyridazinedione) was applied at 4 to 6 lb/A, in spring and fall, with and without (2,4-dichlorophenoxy)acetic acid (2,4-D), on roadsides normally mowed from 2 to 12 times a year. MH at 6 lb/A applied in spring generally reduced grass height. Lower rates and fall applications were generally ineffective. Depending on area, rural or urban, and retardant effectiveness, between zero and five mowings per year were saved. When the MH was effective and the turf was not strong and vigorous, annual weeds such as crabgrass (Digitaria spp. Heist.), foxtail (Setaria spp. Beauv.), and ragweed (Ambrosia spp. L.) often increased and gave the roadside an undesirable appearance. When MH was used without 2,4-D, the roadside generally had a poorer appearance than when not treated. When MH was applied with 2,4-D and no application ‘'skips” or annual weed infestation occurred, the roadside sometimes had a satisfactory appearance. The time when MH can be effectively applied is short (about 2 weeks). Rains, winds, and springtime roadway work make proper timing of applications difficult under Minnesota conditions. Applications of 2,4-D alone or with MH were effective in reducing roadside weeds.

The divisions and subjects of weed biology were identified. Twenty-eight representatives from the herbicide industry ranked the priority of the identified subjects. They also gave their thoughts and impressions on specific questions dealing with weed biology. The divisions which received a moderate to high priority rating are: Identification and Classification of Weeds, Harmful Aspects of Weeds, Weed Growth and Development, and Weed Control. A review of the papers published in Weed Science indicates an increase in the number of papers being published on the subject of weed biology and a decrease in the number of papers dealing with chemical control. The proceedings of the regional weed societies in the U.S.A. had a high percent of the papers devoted to chemical control, with the lowest percentage devoted to weed biology. Comments are made as to why weed biology is important and how research data on weed biology would be used by industry. A comparison of the rating that industry assigned to the various subjects of weed biology to the amount of published literature indicates insufficient work has been done in many areas. It also appears that there is an imbalance in research. More work is being done on certain subjects that industry considers of lesser value than subjects of greater importance.

Field research was conducted during the summers of 1981 and 1982 in order to determine relative infection and population increase of lesion nematodes (Pratylenchus spp.) on seven weed species that commonly occur in field-bean (Phaseolus vulgaris L.) fields in western Nebraska. Weeds were grown at three densities with and without fieldbeans. A representative sample of the root systems from plants in each plot was removed in August and the nematodes were extracted and counted. No difference in nematode infection rate was found among weed population levels. Nematodes per gram of dry root were not different in weeds grown with or without fieldbeans. Weeds grown with fieldbeans had smaller root systems, and consequently total nematodes per root system were less than in weeds grown in the absence of fieldbeans. There was a significant difference among most weed species when nematodes per gram of dry root were estimated. Hairy nightshade (Solanum sarachoides Sendt. ♯3 SOLSA) and barnyardgrass [Echinochloa crus-galli (L.) ♯ ECHCG] supported the highest numbers of nematodes per g oven-dry roots, redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE) had least numbers of nematodes/g oven-dry roots, and infestation levels on other weed species were variable but generally intermediate.

Oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] applied to bermudagrasses [Cynodon dactylon (L.) Pers.] at 4.5 kg ai/ha/yr in September reduced turf quality more than when treatments were applied anytime from April through August. The quality of ‘Tifway’ was reduced more than ‘Tifgreen’, ‘Tifdwarf’, or ‘Ormond’, and Ormond was reduced less than the other cultivars 3 weeks following oxadiazon treatment. Turf cover at the end of the growing season was not reduced with annual oxadiazon application at 4.5 kg/ha, whereas the cover was less in all plots treated with 13.5 kg/ha after four and five annual treatments. When compared with respective untreated cultivars, the cover of Tifway was reduced more from 13.5 kg/ha rate of oxadiazon than the other cultivars. Bermudagrass growth was retarded in the spring following oxadiazon applied the previous year.

The dimethylamine salt of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] combined with toxaphene (chlorinated camphene) or acifluorfen [5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-nitrobenzoic acid] and toxaphene combined with acifluorfen at several rates each were applied in the greenhouse and field to sicklepod (Cassia obtusifolia L.) to determine interactions. Toxaphene plus 2,4-DB treatments produced synergistic or additive responses in the greenhouse and in the field. Antagonistic or additive responses were observed with acifluorfen plus 2,4-DB treatments in the greenhouse, but not in the field. Acifluorfen plus toxaphene produced only additive responses in the greenhouse with synergistic interactions observed under field conditions.

Anecdotal reports suggest waterhemp is becoming more difficult to control with glyphosate. Waterhemp accessions collected primarily in Illinois before 1996, in 1998 to 1999, and in 2003, were evaluated for differential responses to glyphosate treatment. The pre-1996 group consisted of 10 accessions, whereas the 1998 to 1999 and 2003 groups consisted of 45 accessions each. Plants 10 to 12 cm in height from each waterhemp accession were treated with 0 or 220 g ae ha−1 glyphosate. Although shoot dry biomass 14 d after treatment, expressed as a percentage of the untreated, varied within and among accessions, the mean responses of the three groups were similar. However, when glyphosate responses were divided into 10 arbitrary classes (0 to 10, 11 to 20, …, and 81 to 90; > 91% of untreated), the number of plants within each class differed among groups. Most notably, the proportion of plants in the range of 0 to 30% of the untreated control decreased with time when progressing from the pre-1996 to the 2003 accessions. The relative frequency of waterhemp plants that were ≥ 100% of the untreated plants (i.e., uninjured by glyphosate) in the pre-1996, 1998 to 1999, and 2003 groups were 5, 6, and 5%, respectively. In a separate trial, waterhemp populations that exhibited the least sensitivity to glyphosate at 220 g ha−1 were controlled by 870 g ha−1 glyphosate. These results suggest that waterhemp, as a whole, within Illinois has not become less sensitive to glyphosate over the past few years. However, the proportion of plants that are most sensitive to glyphosate may be decreasing within populations.

To validate carboxyterminal processing protease of D1 protein (CtpA) as a target for herbicide discovery, CtpA sense mRNAs were overexpressed to suppress the internal level of CtpA protein in mouseearcress plants. Using antibodies raised against recombinant CtpA protein, we demonstrated that we have generated transgenic mouseearcress plants with reduced levels of CtpA protein and plants with elevated levels of CtpA protein. Transgenic plants with severely reduced levels of CtpA protein exhibited a bleached and chlorotic phenotype and stunted growth. The mutant phenotypes were enhanced by bright illumination. However, plants with a slight reduction of CtpA protein did not exhibit the mutant phenotype and could not be distinguished from wild-type plants under normal growth conditions. Several CtpA enzyme inhibitors were shown to have herbicidal activity in planta. Interestingly, plants producing excessive amount of CtpA protein were shown to be resistant to these inhibitors. Our results suggest that CtpA is essential for plant growth and development, but a reduced amount of CtpA is sufficient to carry out its essential function. CtpA may be a good target for herbicide development, but very high levels of inhibition may be required to produce a herbicidal effect. In addition, overexpressing CtpA in target plants might provide a mechanism for producing plants resistant to the herbicide.

For wild oats, persistence characters such as seed production and seed dormancy may be affected by genetic variation and several environmental factors during the development of the parental plant. However, the effect of varying photoperiods on such characters is unclear. Previous studies have concentrated on natural populations and have not studied the genetic variability within the population. Consequently, a study was conducted to examine how photoperiod (10, 12, 14, 16, and 18 h at 20 C) influenced the persistence of different members of a synthetic population of wild oats. This synthetic population consisted of several isogenic lines with differing degrees of seed dormancy that originated from one region in North America. All lines were photoperiod sensitive, quantitative long day plants, with an increase in time to maturity for all lines (about 78 to 213 d) when photoperiod was reduced from 18 to 10 h. The lines within this synthetic population (with the exception of one, M73) showed a similar degree of photoperiod sensitivity. This may be expected, as the lines are from one region with the same photoperiod environment. It could be concluded that such a photoperiod sensitivity is a beneficial character that has allowed persistence of these lines in this region. When photoperiod was reduced from 18 to 10 h, plants produced fewer seeds (about 141 to 61 primary seeds per plant) with a higher degree of seed dormancy (about 88 to 54% germination in 10−4 M gibberellic acid; GA3). The reduced seed production under the shortest photoperiod (10 h) was due to poor panicle exsertion, which resulted in poor development of basal florets. There was no consistent relationship between photoperiod and other plant characters such as tiller production, caryopsis weight, and water content. However, significant relationships were found between seed dormancy characters and other plant characters such as maturity time, caryopsis weight, and water content under certain photoperiod treatments.

Biennial wormwood and lanceleaf sage have become serious weeds of several crops within the northern Great Plains of the United States and Canada. Both species are prolific seed producers but little is known about their potential for developing persistent seedbanks. Field studies were conducted to determine the influence of duration (7, 8, 11, 19, 20, and 23 mo) and depth of burial (0, 2.5, and 10 cm) on biennial wormwood and lanceleaf sage seed viability and decay. Biennial wormwood and lanceleaf sage seeds were buried in September 2003 (burial 1) and September 2004 (burial 2). In burial 1, biennial wormwood and lanceleaf sage seed viability was 65 and 66%, respectively, after 23 mo of burial. In burial 2, biennial wormwood and lanceleaf sage seed viability was 8 and 3%, respectively, after 23 mo of burial. The difference was likely because of higher soil moisture during burial 2, which promoted seed decay. Controlled-environment studies sought to determine the influence of stratification environments (freezing, chilling, and freeze–thaw) followed by exposure to diurnally fluctuating temperatures on germination of biennial wormwood and lanceleaf sage seeds. Stratified biennial wormwood seed germination was 95% or greater when incubated in fluctuating day/night temperatures of 37/20 or 37/25 C. Stratified lanceleaf sage seeds from freezing and chilling environments did not differ in germination following incubation in fluctuating temperatures and averaged 56 and 55%, respectively. Germination of stratified lanceleaf sage seeds from the freezing and thawing environment was higher than 50% during the thawing cycle, suggesting the possibility of early season emergence of this species. Our study indicates that biennial wormwood and lanceleaf sage have the potential to develop a seedbank that can persist for more than 2 yr. High moisture levels in the soil seedbank can lead to reduced seed survival.

Postemergence applications of flufenprop-methyl [methyl-N-benzoyl-N (3-chloro-4-fluorophenyl)-2-amino-propionate] for wild oat (Avena fatua L.) control in spring wheat (Triticum aestivum L.), durum wheat (Triticum durum L.), and barley (Hordeum vulgare L.) were evaluated in the field, greenhouse, and controlled environmental chambers. Wild oat control with flufenprop-methyl was greater at the five-leaf stage than three and one-half or two-leaf stage of growth. Wild oat control was not reduced when flufenprop-methyl was tank-mixed with bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one, 2,2-dioxide]. Tolerance of spring and durum wheat cultivars to flufenprop-methyl was acceptable; however, tolerance of barley cultivars was considerably more variable. Air temperature after treatment, soil fertility, and moisture did not influence wild oat control with flufenprop-methyl; however, a simulated rainfall of 1 mm within 1/2 h or 4 mm within 4 h after application reduced wild oat control.

Several factors were studied which influenced 3-amino-1,2,4-triazole (amitrole) metabolism in excised leaves of bean (Phaseolus vulgaris L., var. Red Kidney) and Canada thistle (Cirsium arvense (L.) Scop.) ecotypes. Amitrole metabolism in the leaves of both species held in the light was greater than in leaves held in the dark. Increasing the temperature from 15 C to 28 C also stimulated the rate of metabolism of amitrole. However, this effect was much less pronounced when the temperature was increased from 22 C to 28 C. Dipping the leaves in 10−2M ammonium thiocyanate reduced the metabolism of amitrole, whereas similar pre-treatment with 3.5 × 10−3M 6N-benzyladenine enhanced the metabolism of amitrole.

Bermudagrass is a difficult perennial weed to manage in Louisiana sugarcane. Research was conducted to compare interrow tillage practice, postharvest residue management, and herbicide placement on bermudagrass proliferation and sugarcane yield. Tillage frequencies included conventional (four tillage operations per season), reduced (two tillage operations), and no-till. Residue management practices included removal by burning, sweeping from row top into the wheel furrow, and not removed. Spring herbicide placement treatments included broadcast, banded, or no herbicide application. With conventional tillage, broadcast and banded herbicide applications resulted in similar bermudagrass cover in the first and second ratoon crops, but bermudagrass cover was greater when using banded applications (22%) compared with broadcast application (15%) in the third-ratoon crop. Bermudagrass cover was greatest with no-till. When herbicides were banded, bermudagrass cover was greater in reduced tillage than conventional tillage in all three ratoon crops. Postharvest residue management did not affect bermudagrass ground cover. In plant cane, sugarcane yields were lowest when herbicide was not applied. In ratoon crops, sugarcane and sugar yield were reduced when herbicide was not applied regardless of tillage practice. Cane and sugar yield were generally equal when comparing reduced and conventional tillage. Total sugarcane yield (4 crop yr) for the no-till program was reduced 11, 15, and 25%, respectively, when herbicides were broadcast, banded, and when herbicide was not applied, compared with conventional tillage. Failure to remove residue reduced sugarcane yield by 5, 7, and 10% in first, second, and third ratoons, respectively, compared with burning. Eliminating unnecessary tillage practices can increase profitability of sugarcane through reduced costs, but it will be imperative that herbicide programs be included to provide adequate bermudagrass control and that postharvest residue is removed to promote maximum sugarpostane yield.

Little barley (Hordeum pusillum Nutt.) seeds germinated readily without pregermination chilling on substrates moistened with either water or 0.2% aqueous KNO3. Little barley seeds were physiologically mature and viable as early as 11 days after flowering. Pregermination chilling induced dormancy in mature seeds moistened with water, but not those moistened with 0.2% KNO3. Mature seeds frequently germinated better at alternating temperatures from 20C (16 h) to 30C (8 h) than at constant 20C. Germination of seeds after 1 week in a thermogradient table varied from 1% at 34C to 77% at 21C. Seeds were able to germinate over an extended period in the fall and spring. Forage and seed production were highest from the first fall planting date and decreased with later plantings. Plants emerging from seeds planted in March and April did not produce seed.

Hydrilla is one of the most serious aquatic weed problems in the United States, and fluridone is the only U.S. Environment Protection Agency (USEPA)–approved herbicide that provides relatively long-term systemic control. Recently, hydrilla biotypes with varying levels of fluridone resistance have been documented in Florida. Fluridone-susceptible (S) and several fluridone-resistant (R1 to R5) hydrilla biotypes varying in resistance levels were maintained in 950-L tanks under ambient sunlight and day-length conditions. To correlate varying levels of fluridone resistance to ploidy in hydrilla, flow cytometric analysis was performed. Differential ploidy levels (diploid, 2n = 2x = 16; triploid, 2n = 3x = 24; and tetraploid, 2n = 4x = 32) were reported among different hydrilla biotypes, plants within each biotype, and within shoot tissues of the same plant. Triploid plants were predominant in all biotypes. Diploid plants were observed in all hydrilla biotypes except the susceptible hydrilla (S). Plants with tetraploidy were rare within biotypes. The diploid, triploid, and tetraploid plants had nuclear DNA contents of 2.43 to 2.73 pg, 3.44 to 3.71 pg, and 4.64 to 4.90 pg, respectively, and no differences were observed among plants with same ploidy for nuclear DNA content in different hydrilla biotypes. Endoreduplication patterns were observed in diploid plants of R1 and R3 biotypes. However, no plant with higher ploidy levels (triploid or tetraploid) in any hydrilla biotypes showed endoreduplication.