The configuration of the growth pattern for Chrysothamnus viscidiflorus (Hook.) Nutt. was determined from vegetative bud burst to flowering. Important portions of the pattern are: restrictive growth during early spring, accelerated growth in late spring when the optimum susceptibility to herbicides occurs, and a leveling off of growth before flowering. Seedlings and young plants have a more rapid and greater annual stem elongation than mature or senescent plants. Elongation during the accelerated growth period can be predicted from early spring growth with moderate precision when soil moisture and temperatures are not limiting. Populations growing on sites of higher or lower elevations or of pronounced aspect will have growth patterns moderately varying from the modal populations. The greatest factor influencing the growth pattern on years with adequate soil moisture was competition from other species and the combination of competition and age of the rabbitbrush plants.

Control of spurred anoda [Anoda cristata (L.) Schlecht.] in the greenhouse was less than 75% after 28 days with preplant incorporated herbicides except dinitramine [N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine] which gave 88 to 94% control. In greenhouse and field studies with cotton (Gossypium hirsutum L. ‘Coker 210′) preemergence applications of norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] controlled 93 to 100% of the spurred anoda 4 weeks after application. Control with postemergence applications of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-toly)urea] was 46.0 to 92.5%; 90.7 to 100% with prometryn [2,4-bis(isopropylamino)-6-(methylthio-s-triazine]; and 100% with methazole, [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione]. Preemergence applications of norflurazon plus fluometuron, prometryn, or methazole applied postemergence controlled 93, 97, and 100% of spurred anoda, respectively. Fluometuron plus the same three postemergence treatments controlled 63, 95, and 88% of spurred anoda, respectively. Results of our tests suggest that the best control of spurred anoda can be obtained in cotton by a combination of norflurazon applied preemergence at 1.68 kg/ha followed by two postemergence applications of either fluometuron at a rate of 2.24 kg/ha, prometryn at a rate of 1.68 kg/ha, or methazole at a rate of 1.68 kg/ha.

Pea (Pisum sativum L. ‘Elf’) root rot suppression by dinitroaniline herbicides could not be explained by a direct effect on the host. Pre-incubation of pea roots with 0.1 ppmw of oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) or trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) in solution culture did not alter their resistance to root rot. Furthermore, 0.1 ppmw of oryzalin or trifluralin did not alter the exudation of electrolytes or α-amino compounds from pea roots. Most of the dinitroaniline herbicides significantly inhibited mycelial radial growth of pathogen, Aphanomyces euteiches Drechs., at 1.0 ppmw and inhibited asexual spore production at 0.1 to 1.0 ppmw. Dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], and oryzalin inhibited A. euteiches mycelial growth and asexual reproduction more effectively than the other dinitroaniline herbicides studied. The production of motile zoospores, the infecting propagule of the pathogen, was the most sensitive stage in the life cycle and was completely inhibited by 0.01 ppmw of all dinitroaniline herbicides tested. Since this concentration is below that estimated in the soil solution at registered rates of application, inhibition of motile zoospore production is sufficient to explain root rot suppression. Inhibition of pathogen motility resulted in a 2-week delay in the infection of pea roots. This delay allowed sufficient additional plant growth that the peas could better withstand the effects of subsequent disease development.

Investigations with exogenous test solutions showed that abscisic acid (ABA) inhibited germination of nondormant seeds and that gibberellins (GA) promoted the germination of yellow foxtail (Setaria lutescens (Weigel) Hubb.) The effect of the promoters was much more readily demonstrated with excised caryopses than with intact seeds. Cytokinins reversed ABA inhibition of germination; GA did not, but the two promoters in combination were more effective than the cytokinin alone. The reversal occurred only at one end of the embryonic axis, the shoot end. An endogenous inhibitor was extracted from dormant and nondormant yellow foxtail seeds and compared with ABA by chromatography, electrophoresis, and bioassays. The extracted inhibitor was very similar to ABA in six paper-chromatography solvent systems, three paper electrophoresis runs at different pH values, and three bioassays. Paper electrophoresis was an effective means of separating the two plant hormones, ABA and gibberellic acid (GA3).

The few available herbicides for fresh market spinach do not provide adequate weed control, and there is need for additional herbicide tools. Phenmedipham is registered for use in processing spinach but not in fresh spinach, because of potential injury and the short interval between application and spinach harvest. The objectives of this study were to evaluate the tolerance level of fresh spinach varieties to phenmedipham and evaluate the impact of light intensity on tolerance of spinach to phenmedipham. In the greenhouse, nine spinach varieties were treated with phenmedipham (0.55 kg ai ha−1). Spinach varieties exhibited a wide range of tolerance, and dry weights of treated plants ranged from 40 to 78% compared to the nontreated control. Based on the phenmedipham tolerance screen, two varieties with low (Nordic) and high (Regal) tolerance to phenmedipham were treated, then exposed to half (shaded) and full (nonshaded) sunlight. Nonshaded Nordic treated with phenmedipham had 65% lower dry weight compared to similarly treated plants grown under shade, suggesting that spinach tolerance to phenmedipham was mainly affected by light intensity. Measurements of electron transfer intensity in photosystem II also showed tolerance to phenmedipham that varied among spinach varieties and light intensity. The maximum values of electron transfer in photosystem II of Regal treated with phenmedipham were higher than those of similarly treated Nordic. In the field, phenmedipham was applied under varied light and temperature conditions. The impact of light intensity on yield of treated spinach was greater than the impact of temperature. Phenmedipham applied under high light conditions was more injurious than when applied under low light conditions. Results from this study can contribute to successful integration of phenmedipham into currently used fresh spinach weed management, which in turn can allow more efficient production of this crop.

In wetlands, drought or managed late-summer drawdowns create exposed mudflats that provide an excellent substrate for germination of purple loosestrife seeds. If late-emerging purple loosestrife seedlings survive the winter, new or expanding populations of purple loosestrife will result. Spring survival was determined for overwintered purple loosestrife seedlings from seeds planted at weekly intervals in late summer or fall of the previous year. Seedlings of purple loosestrife that emerged from late July to early August had the greatest survival rates and the greatest shoot dry weight, and they were the tallest the following spring. However, 37% of purple loosestrife seedlings that emerged in late August, although stunted, generated a crown that was able to overwinter successfully and regrow the following spring. The number of growing degree days accumulated from planting date to October 6 (the average date of first frost for Minneapolis and St. Paul, MN) was 1,424 for seedlings from seeds planted on July 21 but only 219 for seedlings from seeds planted on September 15. Purple loosestrife seedlings that emerge during late summer through early September in Minnesota may survive the winter to create additional purple loosestrife weed problems in wetland mudflats caused by artificial drawdowns or droughts.

During the planting of alfalfa (Medicago sativa L.), ethyl N,N-dipropylthiocarbamate (EPTC) was applied in subsurface bands beneath the legume seed and each of three triazine herbicides or EPTC was placed in subsurface bands between the rows. Triazines used were 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 2-chloro-4-ethylamino-6-isopropylamino-5-triazine (atrazine), and 2-isopropylamino-4-methoxyethylamino-6-methylmercapto-s-triazine (hereinafter referred to as G-36393). EPTC applied between and within the rows, as well as simazine between the rows and EPTC within the rows, gave superior weed control with little chronic effect on alfalfa. Alfalfa yields following both treatments were increased. Other treatments were unsatisfactory because of poor weed control or because of serious damage to alfalfa.

Greenhouse and laboratory studies were conducted to determine the physiological basis for CGA-248757 and flumiclorac selectivity in five plant species. CGA-248757 and flumiclorac selectively control weeds postemergence (POST) by inhibiting protoporphyrinogen oxidase (Protox). Injury symptoms from CGA-248757 and flumiclorac include rapid desiccation and necrosis similar to injury from diphenyl ether and bipyridinium herbicides. Species sensitivity to CGA-248757 and flumiclorac was evaluated by comparing the dry weight reduction from POST applications. Abutilon theophrasti was sensitive to both herbicides, Amaranthus retroflexus was more sensitive to flumiclorac than CGA-248757, Brassica kaber was sensitive to CGA-248757 but tolerant of flumiclorac, and Zea mays and Glycine max were tolerant of both herbicides. Studies evaluated CGA-248757 and flumiclorac retention, absorption, translocation, and metabolism. Enhanced herbicide metabolism contributed to the tolerance of A. retroflexus to CGA-248757 and B. kaber to flumiclorac. Decreased herbicide retention, absorption, and translocation coupled with increased metabolism contributed to Z. mays tolerance of CGA-248757 and flumiclorac. Decreased herbicide retention and increased herbicide metabolism provided G. max tolerance of both herbicides.

Aminocyclopyrachlor (AMCP) is a synthetic auxin herbicide used for broadleaf weed control in pasture and rangeland. The tolerance and fate of AMCP within pertinent grass species is not well understood. Research was conducted to establish the tolerance of four grass species to AMCP application and observe their absorption, translocation, and metabolism. Results indicate that tall fescue is the most tolerant of AMCP at rates required for weed control. Bahiagrass and bermudagrass are marginally tolerant, and cogongrass is the most sensitive. Tall fescue and bahiagrass absorbed more AMCP than bermudagrass and cogongrass, but cogongrass absorption is the most rapid and complete within 2 days after treatment (DAT). Cogongrass and bermudagrass translocated the least amount out of the target area, whereas bahiagrass and tall fescue translocated the most. Radioisotope imaging revealed that tall fescue may sequester absorbed AMCP in leaf tips. This sequestering may be the basis of the greater tolerance to AMCP by tall fescue relative to the other species evaluated. No metabolism of AMCP was detected in any grass species out to 42 DAT.

Portability is a very important feature of a sprayer for experimental plots on rangeland. The rockiness of many sites and the height and density of many weed stands, such as species of Artemesia, Chrysothamnus, Linaria, Alhagi, and Centaurea, preclude use of push-type sprayers mounted on wheels. Ries and Terry discuss the use of a portable small-plot sprayer but the capacity of their sprayer is not adequate for many situations. Range weed control research is often combined with reseeding and fertilization studies, and a sprayer with considerable capacity is needed for large plots. Swath widths of at least 10 feet are desirable.

The design and use of a variable-dosage spraying machine for the experimental evaluation of herbicides has been reported by Pfeiffer et al. (1). This equipment sprays at constant volume while simultaneously diluting the spray mixture exponentially. The machine is composed of a series arrangement of diluent tank, concentrate tank, pump, and nozzles. The concentrate tank is equipped with a rapid mechanical agitator. The pump propels the spray liquid from the concentrate tank through the nozzles in the conventional manner. The liquid withdrawn from the concentrate tank is replaced by an equal volume of water or other diluent from the diluent tank. Thus the concentration of active ingredient in the spray decreases logarithmically with the volume of spray delivered. Since spray volume is constant with time, by moving the sprayer at constant speed, the rate of application of the active ingredient becomes a logarithmic function of distance along the plot. The machine is mounted on a four-wheel-drive light truck and draws power for the pump and agitator from the power take-off.

A system involving resting cells of Euglena gracilis provides a rapid and convenient test system for screening potential herbicides which act as inhibitors of chlorophyll synthesis. The system appears to distinguish between inhibitors of chloroplast formation, such as 3-amino-1,2,4-triazole, and inhibitors of chlorophyll formation per se, such as ethionine.

The effects of various rates of 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid (endothall), isopropyl N-phenylcarbamate (IPC), and 2-methoxy-3,6-dichlorobenzoic acid (dicamba) on Bromus tectorum L. (downy brome) on four soils with surface litter and incorporated organic matter treatments were studied. Significant differences were found in reaction of downy brome seedlings to the herbicides in the four soils. The soil with the highest organic matter content generally inhibited herbicide action to the greatest extent. Straw mulch alone caused a significant decrease in growth of downy brome seedlings. Action of IPC was most inhibited by straw, and endothall the least.

Procedures were developed for simultaneous control of big sagebrush (Artemisia tridentata Nutt.), green rabbitbrush [Chrysothamnus viscidiflorus Var. Viscidiflorus (Hook.) Nutt.] and downy brome (Bromus tectorum L.) with the herbicide karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1, 1-dimethylurea]. After a season of fallow, the herbicide-treated areas were seeded with perennial grasses. During the 4 yr of testing at several locations, karbutilate at 1.1 kg/ha controlled the shrubs and downy brome. A herbaceous fallow was maintained with 0.6 kg/ha of the herbicide, but 1.1 kg/ha was necessary for green rabbitbrush control. Perennial grass seedling establishment was highly variable among sites and years of testing. If germination of the seeded species occurred in the fall, stands were poor. When germination was delayed by the onset of cold weather until spring, excellent stands were obtained on plots treated 1 yr previous to seeding with 1.1 kg/ha of karbutilate. Residual herbicide activity was harmful at the time of fall seeding but herbicide residues declined by spring as shown by bioassay of soils.

Experiments were conducted using the Avena coleoptile straight-growth test to determine the influence of diclofop {2-[4-(2,4-diclorophenoxy)phenoxy] propanoic acid}, as the acid or methyl ester, and MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} on coleoptile growth of several species. Diclofop ester was a three-fold stronger inhibitor of oat (Avena sativa L. ‘Terra’) coleoptile growth than the free acid. The concentration of diclofop ester needed to inhibit 50% of the oat coleoptile growth was not influenced by IAA (indole-3-acetic acid) concentration. Oat coleoptile growth in the presence of 5 μM IAA plus 5 μM diclofop ester increased for 2 h after treatment and then decreased, so that the coleoptile length was less at the end of the 24-h assay period than at the beginning of the diclofop-ester treatment. Diclofop ester inhibited the coleoptile growth of wild oat (Avena fatua L.) > oat > wheat (Triticum aestivum L. ‘Era’) > corn (Zea mays L. inbred ‘A-239’) > corn inbred ‘CI-66’. MCPA added to the treatment solution did not overcome oat coleoptile growth inhibition from diclofop ester or acid.

Degradation of flurtamone in a Greenville sandy clay loam, a Cecil loam, and a Dothan loamy sand with 0, 1, or 2 yr of previous flurtamone field use was evaluated under controlled conditions. Soil sterilization by autoclaving significantly reduced flurtamone dissipation rate in all soils. Enhanced degradation of flurtamone was observed in a Greenville sandy clay loam after 1 yr of previous flurtamone field use and in a Cecil loam after 2 yr of previous flurtamone field use. No enhancement of flurtamone degradation was observed in a Dothan loamy sand. Flurtamone degradation kinetics in these studies was described as a first-order process. Microbial populations in each soil showed no major changes in total bacterial numbers due to preexposure to flurtamone in the field.

Dwarf spikerush [Eleocharis coloradoensis (Britt.) Gilly], a perennial aquatic plant, is composed of many individual rosettes connected by rhizomes. Each rosette has needlelike culms attached to a stalk, a crown with an apical meristem, and many fibrous roots. It reproduces by achenes, subterranean tubers, and crown tubers. Dwarf spikerush achenes were harvested three times in 1 yr after the water level had been manipulated to promote flowering. The annual yield of achenes following this treatment was 79 kg per ha. Subterranean tubers began to form in September and formation was maximum in October. Individual plants grown for 1 yr developed an average of 351 tubers. Maximum density of tubers formed in hydrosoil was 7 per cm2. Longevity studies showed that the percentage germination of achenes and tubers decreased, respectively, from 48 to 32% and from 100 to 46% when stored wet at 4 C for 4 yr. Plants grown for 6 months from a single subterranean tuber, rosette, or achene spanned 150, 127, and 99 cm, respectively. The species thrived in a wide range of water qualities and on soft hydrosoils largely made up of silt, clay, and organic matter. On plants immersed in 0 to 100% sea water for 1 month, culms were injured in 30% sea water and killed in 40% sea water. Surviving plants showed some new growth after transfer to fresh water. Some tubers were incubated in diluted sea water. They germinated in solutions up to 80% sea water. Plants grown in water under different light intensities grew best at the maximum of 3,900 lux. More rosettes, culms, and inflorescences were produced with a 14-h photoperiod than 11- or 17-h photoperiod. Dwarf spikerush displaced other species by invading them when growth of the other plants was suppressed. The erect crowded culms of dwarf spikerush mechanically resisted incursion of other aquatic plants.

Seed fields of white clover (Trifolium repens L. ‘New Zealand’ and ‘Louisiana S-1′) were treated with the dimethylamine salt and the isooctyl ester of 4-(2,4-dichlorophenoxy)-butyric acid (2,4-DB). Rates of application were 0.56, 1.12, and 1.68 kg/ha. Applications were made at the vegetative, bud, and flowering stages of growth. All treatments applied at the vegetative and bud stages of growth significantly reduced white clover seed production. Reductions in clover seed production usually became more severe as the rate of 2,4-DB increased.