The abilities of herbicides to either produce superoxide radical or react with this radical were examined. The effect of the herbicides on the superoxide-induced reduction of p-nitro blue tetrazolium chloride was used as an index. Paraquat (1,1-dimethyl-4,4′-bipyridinium ion) enhanced and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] inhibited the reduction of p-nitro blue tetrazolium chloride. Paraquat was reduced photochemically (riboflavin/methionine) or enzymatically (xanthine/xanthine oxidase) and produced superoxide radical upon reoxidation. Diuron and monuron [3-(p-chlorophenyl)-1,1-dimethylurea] interacted with photochemically produced superoxide radical, but not with enzymatically produced superoxide radical. The product of the monuron/superoxide interaction was a demethylated, dechlorinated, water-soluble compound containing phenolic hydroxyl group(s), and was not toxic to oats (Avena sativa L.). The enzyme superoxide dismutase prevented the formation of this product.

From 1962 to 1967, we evaluated herbicides for control of natural infestations of reed canarygrass (Phalaris arundinacea L.) on canal banks of the Huntley, Montana irrigation project. Two,2-dichloropropionic acid (dalapon) and 3-amino-1,2,4-triazole ammonium thiocyanate (hereinafter referred to as amitrole-T) controlled reed canarygrass. These herbicides were compared with a number of others. Spring foliage treatments with a combination of amitrole-T at 2 1b/A and dalapon or trichloroacetic acid (TCA) at 5 or 10 1b/A were more effective than amitrole-T at 4 1b/A. Amitrole-T was more tolerant to fine grasses such as Kentucky bluegrass (Poa pratensis L.) or redtop (Agrostis alba L.) than dalapon and in some situations it was more desirable than dalapon. Dalapon and TCA were more effective as late fall or early winter treatments to control reed canarygrass during the following growing season. Rates of 20 or 40 1b/A controlled the grass for one season even at the water's edge where it is usually more persistent. At 5 to 10 1b/A, 2,3,5-trichloro-4-pyridinol (pyriclor) controlled reed canarygrass, and it also was effective at 2 1b/A with 2 1b/A of amitrole-T.

The metabolism of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] in cell suspension cultures of white clover (Trifolium repens L. ‘Regal Ladino’) was investigated using (ring)- 14C 2,4-DB. The herbicide and its 14C-labeled metabolites were isolated from treated cells and medium after 48 h by partition and thin layer chromatography (TLC). The major portion of the radiolabel was in the glycoside fraction (47%) and incorporated into the cell structural material (34%). The remainder of the 14C remained either as the parent herbicide (8%) or an amino acid conjugate of 2,4-DB (10%).

Seeds of barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common purslane (Portulaca oleracea L.), fimbristylis [Fimbristylis miliacea (L.) Vahl.], goosegrass [Eleusine indica (L.) Gaertn.], monochoria [Monochoria vaginalis (L.) Presl.], pale smartweed (Polygonum lapathifolium L.), rice flatsedge (Cyperus iria L.), slender amaranth (Amaranthus viridis L.), smallflower umbrella plant (Cyperus difformis L.), and sour paspalum (Paspalum conjugatum Bergius), were placed in nylon mesh bags and buried at 0 (surface), 2.5, 7.5, 15, and 25 cm depths in the soil in November 1974 for 10, 20, 30, 60, 90, 120, 180, 240, 300, and 365 days. They were then recovered from soil to test their germination in petri dishes. Seeds on the soil surface had lower percent germination than those that were buried. Statistical data showed that the total percent germination was not significantly different for the seeds buried at 2.5 cm and deeper in soil when examined at the same burial intervals. During the experiment, the total percent germination of seeds was classified into three groups: (a) percent germination remained constant and relatively high, as for smallflower umbrella plant, common purslane, goosegrass, and slender amaranth; (b) percent germination remained at a plateau for 240 days and then gradually declined at 300 and 365 days, as for sour paspalum; and (c) percent germination was low at the beginning and the end of the experimental period but high in the middle, as for barnyardgrass, monochoria, pale smartweed, rice flatsedge, and fimbristylis. During the experiment, common purslane, barnyardgrass, and monochoria reached a germination peak within the first 5 days. Seeds of the 7 other species germinated within 3 to 5 days or 6 to 10 days, depending on the combination of innate dormancy, temperature, and light intensity.

The relative effectiveness of eight acetanilide herbicides for controlling annual weeds in processing peas (Pisum sativum L.) was evaluated in field studies and the susceptibility of peas to injury from these herbicides was studied in both the field and greenhouse. Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] was the most phytotoxic to peas grown in washed silica sand in the greenhouse when the herbicides were applied at concentrations of 2 and 8 mg/L. Field trials conducted over a 2-yr period and simulated rainfall experiments in the greenhouse demonstrated that the phytotoxicity to peas by acetanilide herbicides applied preemergence at 2.2 and 4.5 kg/ha was greatly influenced by subsequent rainfall. When 2.5 cm of simulated rainfall were applied immediately after herbicide application, pea injury increased. Injury to peas was avoided in the field by delaying alachlor application at 2.2 kg/ha until peas began to emerge. This treatment also gave excellent control of annual grass weeds. Greenhouse studies demonstrated that injury to peas by all eight acetanilide herbicides at 2.2 and 4.5 kg/ha could be avoided by delaying application until pea emergence. Alachlor, propachlor (2-chloro-N-isopropylacetanilide), and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] gave slightly superior weed control than butachlor [N-(butoxymethyl)diethylacetanilide] and H 22234 [N-chloroacetyl-N-(2,6-diethylphenyl)-glycine ethyl ester].

Methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] were evaluated in separate experiments for postemergence control of large crabgrass [Digitaria sanguinalis (L.) Scop.] and goosegrass [Eleusine indica (L.) Gaertn.] and on tolerance of centipedegrass [Eremochloa ophiuroides (Munro) Hack.], St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’]. Methazole was also evaluated on tolerance of Kentucky bluegrass (Poa pratensis L. ‘Common’). Metribuzin applied at 0.6 kg/ha and methazole at 1.1 kg/ha as single treatments controlled 82 and 87% goosegrass, respectively. Repeated treatments were needed for similar control of large crabgrass. These treatments did not permanently injure bermudagrass or centipedegrass. St. Augustinegrass was severely injured when treated with single applications of methazole at 1.1 kg/ha or metribuzin at 0.6 kg/ha while Kentucky bluegrass was severely injured by methazole applied at any rate. Methazole caused moderate to severe injury to bermudagrass when applied at 2.2 kg/ha in each of two applications and to centipedegrass when applied at 4.4 kg/ha in each of two applications.

Five herbicides (cloproxydim, fluazifop, haloxyfop, quizalofop, and sethoxydim) were compared from 1984 to 1988 at 250 and 400 g ha−1 for controlling quackgrass within different crop competition and tillage conditions at the Lacombe Research Station. Crop competition usually augmented quackgrass control with the herbicides in conventional-tillage plots although direct statistical comparisons were not made. Without crop competition, haloxyfop and quizalofop at 250 g ha−1 were more effective than the other herbicides in conventional tillage 1 mo after treatment (MAT). In a conventional-tillage situation on a unit active ingredient basis, the herbicides ranked in order of decreasing activity as follows: quizalofop ≥ haloxyfop > fluazifop > cloproxydim > sethoxydim. In a zero-tillage situation, none of the herbicides reduced quackgrass shoot weights by 50% 3 MAT. However, haloxyfop and quizalofop were more effective in suppressing quackgrass shoot weight than the other herbicides in the zero-tillage experiments 3 MAT.

Three annual plant species — erect plantain (Plantago erecta Morris), common chickweed [Stellaria media (L.) Cyrill.], and silver hairgrass (Aira caryophyllea L.)—are commonly found and may dominate a unique flora on areas sprayed with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) in cismontane rangelands of California. The basis of this phenomenon is shown to be temperature-related germination requirements, novel seed characteristics, and lack of competition.

Sorption and mobility of 14C-bentazon were evaluated using soil solution and soil-thin-layer chromatography, respectively on three Coastal Plain soils. The proportion of bentazon adsorbed, was pH and concentration dependent and ranged between 28 to 47, 31 to 61, and 17 to 68% for the Dothan loamy sand, Greenville clay, and Troup loamy sand, respectively. Bentazon sorption decreased as soil pH increased from 5.4 to 5.8 on the Troup loamy sand, regardless of bentazon concentration. Sorption of 1 and 10 ppm bentazon decreased as soil pH increased from 5.0 to 5.7 on the Greenville clay and 6.1 to 6.4 on the Dothan loamy sand. Bentazon was least mobile on the Greenville clay and mobility increased as pH increased. Mobility of bentazon was greatest on the Troup loamy sand and was not pH dependent. Bentazon mobility decreased as soil pH increased for the Dothan loamy sand.

Hydroponic treatment with EPTC (S-ethyl dipropylthiocarbamate) inhibited leaf growth and stimulated stem growth of hybrid corn (Zea mays L. ‘Wisconsin 473′). Root treatment with GA3 (gibberellic acid) prevented leaf stunting from EPTC. Most abnormalities in foliar display and height from treatment with 50 μM EPTC were prevented by increasing GA3 levels from 0.5 μM to 10 μM over a week. The effect of EPTC on endogenous gibberellin activity was measured by bioassay of shoot extracts. EPTC (6.7 kg/ha) reduced the levels of total endogenous gibberellin-like substances in eight-day-old seedlings grown in treated soil. Under the environmental condtions of the experiment, this corresponded to the first discernable signs of injury. In addition EPTC induced an abnormal distribution of endogenous gibberellins in the shoots of older corn plants. Leaves of two-week-old EPTC-treated plants contained less gibberellin activity than the leaves of controls. Stems of herbicide-treated plants contained the same levels of gibberellin-like substances as the controls.

Field experiments were conducted at Lincoln, NE, in 1983 and 1984 to determine the effectiveness of subsurface jet injection of herbicides on a simulated shattercane [Sorghum bicolor (L.) Moench # SORVU] infestation in corn (Zea mays L.). Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and EPTC (S-ethyl dipropyl carbamothioate) plus dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide), incorporated with a disc or applied from the subsurface and surface with a jet injector attached to a sweep plow, generally produced higher corn yields and shattercane control than herbicides applied with the sweep to the subsurface only. EPTC plus dichlormid controlled shattercane better than alachlor. Cultivation improved shattercane control by at least 10% in conjunction with most jet injection and disc-incorporated alachlor treatments. Cultivation increased corn yields by about 10 to 20% when averaged over all herbicides and application patterns. A subsurface plus surface herbicide injection system supplemented with cultivation would be a possible method of incorporating herbicides in reduced tillage to selectively control shattercane in corn.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) required more thorough soil incorporation with a disk, probably to prevent loss by volatility, than did 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin). Mechanical incorporation of nitralin could be delayed for 96 hr after application, whereas trifluralin needed to be incorporated within 24 hr to control weeds. Gas chromatographic analyses of soil showed that trifluralin decreased rapidly during the first 24 hr that incorporation was delayed. Application of trifluralin with undiluted crop oil on dry soil did not prolong the persistence prior to incorporation compared to applications with water.

Laboratory assays were conducted to determine the sensitivity of tomato and tobacco cell suspension cultures and tomato and pepper cotyledons to clomazone. A comparison of fresh weight and carotenoid content indicated up to a three-fold difference between the clomazone-tolerant tobacco and clomazone-susceptible tomato cell suspension cultures. In contrast, an approximate 60-fold difference between the tolerant pepper and susceptible tomato cotyledons was observed when total chlorophyll and carotenoid contents were measured. The effect of clomazone and its possible metabolites on in vivo and in vitro extractable IPP isomerase (EC 5.3.3.2) and prenyltransferase (EC 2.5.1.29) activity was investigated. There was no clear inhibitory effect of clomazone or possible clomazone metabolites upon enzyme activity in tomato or tobacco cell suspension cultures or on light or dark grown tomato or pepper cotyledons. No specific enzymatic target site of clomazone was identified in correlation with the reduction in total chlorophyll or carotenoid content.

The active concentration of a pesticide declines with time due to volatilization, absorption and translocation, microbial degradation, adsorption on soil particles and plant parts, chemical reactions, photodecomposition, and other reactions with the environment. However, slow-release formulations can provide a continuing input of pesticide. This leads to a rise and subsequent fall in the active concentration. Because diffusion is a factor in most controlled release methodologies, the concentration to be expected for release by diffusion of a substance, which then decays with time by a first order rate law, is examined theoretically. This provides guidance to the experimenter for separating the effects due to diffusion from these attributable to other and newer concepts such as water-degradable polymers. An approximate result of this exact solution is that the persistence of the substance can be increased. More precisely, the long-term behavior is like that of a more persistent pesticide with smaller first-order rate constant.

A study under glasshouse conditions determined the effect of germination stimulants, potassium nitrate and ethephon, on emergence of several pure lines of wild oat from soil. Effect of the two chemicals on stimulating emergence was variable and no synergism noted when used together. Examination of exhumed seed showed that these treatments reduced seed viability. By counting the number of dead and adding to those that emerged, total seed removed from the soil was obtained. All treatments removed seed from the soil seedbank, especially when seed was old, near the soil surface, was primary seed, or from low or intermediate dormancy lines. However, because of the insensitivity of a large proportion of the seed and the high rates required it is unlikely that either potassium nitrate or ethephon has practical use for field application.

The advent of site-specific weed management has generated research aimed at predicting weed spatial distributions from existing weed maps or correlations with soil properties and edaphic factors. Forecasting the spatial distribution of annual weeds requires knowledge of fecundity, dispersal, management, and suitable habitat distribution. We hypothesized that wild oat habitat was limited by field-scale heterogeneity in plant-available water. We eliminated seed number and dispersal limitations by seeding wild oat in areas with and without historical wild oat patches in three similarly managed spring wheat fields that differed in soil properties and wild oat infestations and were situated within a 160-km radius of Great Falls, MT. Wild oat habitat was quantified by wild oat leaf area growth rate, mature shoot biomass, seeds produced per plant, biomass water use efficiency, and competitive ratio with spring wheat. Soil texture and plot elevation correlated with existing wild oat patch areas in individual fields, but no site properties consistently correlated with wild oat patch areas in all three fields. Soil water use (SWU) and almost all habitat-defining variables for wild oat were similar between historic patch and nonpatch areas. Wild oat grew and produced seed regardless of existing patch boundaries and field-scale heterogeneity in SWU. This research suggested that (1) wild oat habitat may be unlimited in cereal grain cropping systems of the Northern Great Plains and (2) soil properties are a poor predictor of weed distribution for a generalist such as wild oat.

Flooding soil with 5 to 10 cm of water for 7 to 14 days killed all freshly planted johnsongrass (Sorghum halepense (L.) Pers.) rhizomes in greenhouse and field experiments. A delay in flooding until culms emerged greatly reduced control. Flooding the soil in which 4-week-old johnsongrass plants grew had little effect at 15 C, but plants were killed after 8 weeks of flooding at 40 C. Death of buds on immersed johnsongrass rhizomes occurred more rapidly at 40 C than at 10, 20, 25, or 30 C. Flooding for 8 days at 40 C killed all rhizomes, but 16 days of flooding were required to kill all rhizomes at 30 C. Few buds were killed when flooded at 10 or 20 C, but germination was delayed. Immersing rhizomes in water and soil provided better control than immersing them in water without soil.

Investigations during the past three decades have confirmed that field bindweed (Convolvulus arvensis) is exceedingly difficult to eradicate. Since the introduction of sodium chlorate by Latshaw and Zahnley various other soil sterilants have been used successfully for spot treatments. Timmons reported the effect of various systems of intensive cultivation on bindweed control as influenced by root reserves. Phillips and Timmons reported the response of bindweed to crop competition and combinations of cropping, cultivation and 2,4-D. The introduction of 2,4-D (2,4-dichlorophenoxyacetic acid) provided a new tool for bindweed control and an impetus for continued research.

A significant amount of amiben (3–amino–2,4–dichlorobenzoic acid) was leached from the 0 to 1-inch soil depth with 1 and 2 inches of applied water. Weed control could be obtained from amiben at 1 lb/A if rain came within 3 or 4 days after application. One-half inch of water applied immediately after application markedly increased the toxicity of 1 lb of amiben per acre to Brassica juncea (L.) Coss and Panicum miliaceum L.; a similar response from 2 lb/A was obtained with 1/4 inch of water. As the amiben rate was increased, less water was required for optimum weed control. Increased water and/or amiben applications were required with Brassica campestris L., which is somewhat resistant to amiben.

Waterhemp [Amaranthus tuberculatus (Moq.) J. D. Sauer] is a troublesome weed occurring in cropping systems throughout the U.S. Midwest with an ability to rapidly evolve herbicide resistance that could be associated with competitive disadvantages. Little research has investigated the competitiveness of different A. tuberculatus populations under similar environmental conditions. The objectives of this study were to evaluate: (1) the interspecific competitiveness of three herbicide-resistant A. tuberculatus populations (2,4-D and atrazine resistant [2A-R], glyphosate and protoporphyrinogen oxidase [PPO]-inhibitor resistant [GP-R], and 2,4-D, atrazine, glyphosate, and PPO-inhibitor susceptible [2AGP-S]) with soybean [Glycine max (L.) Merr.]; and (2) the density-dependent response of each A. tuberculatus population within a constant soybean population in a greenhouse environment. Amaranthus tuberculatus competitiveness with soybean was evaluated across five target weed densities of 0, 2, 4, 8, and 16 plants pot−1 (equivalent to 0, 20, 40, 80, and 160 plants m−2) with 3 soybean plants pot−1 (equivalent to 300,000 plants ha−1). At the R1 soybean harvest time, no difference in soybean biomass was observed across A. tuberculatus populations. At A. tuberculatus densities <8 plants pot−1, the 2AGP-S population had the greatest biomass and stem diameter per plant. At the R7 harvest time, the 2AGP-S population caused the greatest loss in soybean biomass and number of pods compared with the other populations at densities of <16 plants pot−1. The 2AGP-S population had greater early-season biomass accumulation and stem diameter compared with the other A. tuberculatus populations, which resulted in greater late-season reduction in soybean biomass and number of pods. This research indicates there may be evidence of interspecific competitive fitness cost associated with the evolution of 2,4-D, atrazine, glyphosate, and PPO-inhibitor resistance in A. tuberculatus. Focus should be placed on effectively using cultural weed management practices to enhance crop competitiveness, especially early in the season, to increase suppression of herbicide-resistant A. tuberculatus.