An experiment involving six winter wheat (Triticum aestivum L.) cultivars, an early-April herbicide application on wheat and on four dates after wheat harvest, and the growth of a subsequently planted corn (Zea mays L.) crop was conducted at North Platte, NE. ‘Centurk 78’ suppressed barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] more than ‘Bennett’ and ‘Eagle’ in the growing wheat and after wheat harvest in July, but there were no differences in weed yield among cultivars in corn planted 11 months later. Herbicides applied to the tillering wheat in early April improved weed control in wheat and the subsequent corn crop. Also, herbicides were applied 5, 25, 45, and 300 days after wheat harvest. Weed growth increased and soil water decreased as spraying dates were delayed. Herbicides applied 5 days after harvest did not maintain adequate weed control in the corn planted 11 months after wheat harvest and low corn yield resulted. Plots receiving herbicides 300 days after wheat harvest had the least soil water in the fall after wheat harvest but the best weed control in corn and highest corn yields because of better weed control in corn.

Ceutorhynchus litura dispersed 9 km in 15 yr from its point of release in 1972 with incident of infestation of Canada thistle plants at one study site reaching 92% in 1987. Plants generally survived larval feeding in the spring, but holes created by departing larvae provided entrances for arthropods, nematodes, and diseases. Subsequent mortality rates were high for belowground Canada thistle shoots. However, the number of new shoots from underground roots the following spring usually offset the mortality that had been indirectly caused by C. litura.

The wild oat (Avena fatua L.) is one of the most common annual weed species in the northern portion of the great plains region of North America. It has been estimated that up to 70 bushels per acre of wild oat seeds occur in the soil of seriously infested fields. As an impurity in threshed grain it frequently amounts to 10 per cent or more as dockage. To become a serious problem under the climatic conditions and cropping practices of this region, the seed of an annual weed such as wild oats must undergo a period of dormancy and require exacting conditions for its germination. Therefore, investigations to study the factors affecting dormancy and the optimum conditions under which weed seeds will germinate have received considerable attention.

A biotype of annual bluegrass with suspected resistance to pronamide was collected from a golf course in Georgia. The objectives of this research were to determine the level of resistance to pronamide and the mechanisms associated with resistance. From POST applications, the pronamide rate that reduced shoot biomass 50% from the nontreated bluegrass measured>10 times higher for the resistant (R) biotype as compared with susceptible (S) biotypes. The R biotype was not controlled by PRE applications of dithiopyr or prodiamine, but was controlled >92% by PRE applications of pronamide at 0.56 and 1.68 kg ha−1. Mature plants (3- to 5-tiller) of the R biotype absorbed 32% less [14C]pronamide than the S biotype after 72 h in hydroponic culture and accumulated 39% less radioactivity per gram basis of dry shoot mass. The R biotype metabolized [14C]pronamide similar to the S biotype, averaging 16% of the extracted radioactivity. The resistance to POST pronamide applications in the R biotype is associated with reduced absorption and translocation compared with the S biotype.

The percentage of quackgrass (Agropyron repens (L.) Beauv.) rhizome buds producing shoots was greater with one-inch than with six-inch or longer rhizomes. The longer the rhizome cutting, the stronger the shoot and the greater the recovery from deep planting. Recovery of rhizomes covered with four or more inches of soil was poor. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) at 1½ and 3 lb per acre did not affect the number of shoots produced. It was more effective when applied ½ inch above rhizomes than one inch or three inches above them.

First of all I would like to bring greetings from the Canada Weed Committee (CWC). Under one name or another this Committee has met every year since 1929 when it was organized by a handful of workers to coordinate their tests with sodium chlorate, sodium arsenite, sulphuric acid, etc. The CWC still meets as a working planning committee to review current work, up-date recommendations and coordinate testing for the forthcoming year.

A simple, inexpensive soil perfusion unit for use in studying the microbial decomposition of pesticides is described. This unit has the advantage of being equally adaptable to positive or negative pressure systems.

Acetolactate synthase (ALS) inhibitors are widely used for POST control of sedges in turfgrass. A suspected resistant (R) biotype of annual sedge was collected from a bermudagrass turf in Georgia with a history of exclusive use of halosulfuron. Research was conducted to evaluate the resistance level of this biotype to halosulfuron, efficacy of ALS-inhibiting herbicides and other mechanisms of action for control, and the molecular and physiological basis for resistance. In greenhouse experiments, the halosulfuron rate required to reduce shoot biomass 50% in comparison with the nontreated at 8 wk after treatment (WAT) were 8 and > 1,120 g ai ha−1 for the S (susceptible) and R biotypes, respectively. Imazapic, sulfosulfuron, and trifloxysulfuron reduced biomass of the S biotype greater than 60% at 8 WAT, but biomass was reduced less than 20% for the R biotype. Glufosinate, glyphosate, MSMA, and sulfentrazone reduced shoot biomass of the R biotype by 93, 86, 97, and 45%, respectively. In laboratory experiments, the halosulfuron concentration required to inhibit ALS activity by 50% in excised leaf tissues was 5.8 and > 1,000 μM for the S and R biotypes, respectively. Gene sequencing of the R biotype revealed a Pro-197-Ser substitution that confers resistance to ALS inhibitors. This is the first report of ALS-inhibitor resistance in annual sedge and herbicide resistance in a sedge species from a turfgrass system.

Four concentrations of 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 1-n-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon) and 3-phenyl-1,1-dimethylurea (fenuron), adsorbed on photometrically uniform filter paper, were irradiated with ultraviolet light 253.7 millimicrons) or sunlight. Marked changes in the absorption spectra after irradiation indicated photodecomposition of the four herbicides was different with the two light sources.

Twenty-nine s-triazines were evaluated as subsurface and surface preemergence sprays for the control of crabgrass in corn, grain sorghum, soybean, and cotton and as directed postemergence sprays in cotton. In preemergence experiments corn was tolerant to most chloro-alkylamino-s-triazines but was severely injured by most methoxy- and methylmercapto-alkylamino-s-triazines. 2-Chloro-4,6-bis(isopropylamino)-s-triazine [propazine], 2,4-bis(ethylamino)-6-trichloromethyl-5-triazine, and 2-chloro-4-isopropylamino-6-methylamino-s-triazine were about equally effective for selective preemeregnce weed control in grain sorghum. 2,4-Bis(ethylamino)-6-trichloromethyl-s-triazine and perhaps 2-methoxy-4,6-bis [(3-methoxy)propylamino]-s-triazine were sufficiently active and selective to suggest additional evaluation as preemergence herbicides for soybeans. Cotton exhibited tolerance to certain methylmercapto derivatives; 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine [prometryne] as a preemergence and as a directed postemergence spray appeared especially promising for control of weeds in cotton. Generally methoxy- and methyl-mercapto-alkylamino-s-triazines as preemergence and postemergence sprays were more effective for controlling crabgrass than corresponding chloro-alkylamino-s-triazines. The initial and residual toxicities of 14 of the more promising s-triazines were compared in four soils of the southern United States. Initial effective levels of the methoxy and methylmercapto derivatives varied more among soils than those of corresponding chloro derivatives. In most cases methoxy s-triazines were more toxic to the fifth oat crop than corresponding chloro s-triazines whereas chloro s-triazines exhibited the greatest initial toxicities. Certain methylmercapto derivatives appeared fairly persistent also.

The persistence of soil-surface applied ethyl N,N-di-n-propylthiolcarbamate [EPTC] was studied at air velocities of ⅓ to 4 mph in special air-flow equipment. Persistence was inversely related to velocity though the effect was quantitatively changed by soil composition and the materials used in formulating the EPTC spray.

The efficacy of Alternaria helianthi on imazaquin-susceptible and -resistant biotypes of common cocklebur was evaluated with and without imazaquin. A. helianthi caused severe damage to both biotypes when applied at 80,000 conidia ml−1 at the five- to six-leaf stage. Symptoms included necrotic lesions, stunting, and mortality. Mortality from imazaquin at 140 g ai ha−1 was 0 and 100% and mortality from A. helianthi at 80,000 conidia ml−1 was 33 to 75% and 67 to 100% for resistant and susceptible biotypes, respectively, and surviving plants showed reduction in height, dry weight, and number of new leaves. The combination of imazaquin at 18 g ai ha−1 and A. helianthi at 40,000 conidia ml−1 was not synergistic or antagonistic in killing common cocklebur.

Runoff water was sampled over a 2-year period from an 8-ha site that had been treated and retreated with 4-amino-3,5,6-trichloropicolinic acid (picloram) at the rate of 1.12 kg/ha in the spring of 1969 and 1970. Runoff water was sampled adjacent to the plots and in two creek systems up to 2.0 km from the plots. Samples taken adjacent to the plots declined to less than 10 ppb by 10 to 12 weeks after application. Eight days after application, water sampled 1.2 km from the plots contained less than 1 ppb of picloram. Less than 1.0 ppb levels were occasionally detected 1.6 km from the plots 8 months after treatment.

The influence of soil moisture on wild oat control from soil-incorporated methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)-phenoxy] propanoic} was determined in the greenhouse. Wild oat control with soil-incorporated diclofop at 1.5 or 3 ppmw increased linearly when soil moisture in a Tiffany sandy loam increased from 18.5 to 23.5% (75% to 125% of field capacity). The efficacy of soil-incorporated diclofop was not reduced when soil moisture was allowed to decrease from 21 (field capacity) to 18.5, 16, 13.5, or 11% (wilting point) before rewatering to 21%. The soil moisture level at the time of herbicide application determined the degree of wild oat control with soil-incorporated diclofop. Wild oat control with diclofop increased when a Tiffany sandy loam with 16% moisture (50% of field capacity) at the time of herbicide application, was watered to field capacity after 8 or 12 days delay, and control did not change with watering to field capacity at the time of herbicide application or when delayed 4 or 16 days. The movement of 14C-diclofop in soil columns was greater within coarse than fine textured soils and increased with water volumes applied, regardless of soil type. Further, the leachability of 14C-diclofop was two and a half times greater than that of 14C-trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine).

Nine soil-applied herbicides were evaluated in the field in cotton (Gossypium hirsutum L.) and soybeans [Glycine max (L.) Merr.] and in the greenhouse without crops to determine their effects on the control, regrowth, and tuber production of yellow nutsedge (Cyperus esculentus L.). Fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl) phenyl]-4(1H)-pyridinone} and norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] provided the best (100%) control in the greenhouse. Tubers exposed to herbicide-treated soil in the greenhouse for 4 or 8 weeks produced fewer new tubers when transplanted into nontreated soil than nontreated tubers did. Yellow nutsedge shoot and tuber populations in the field were significantly reduced by all herbicides, except for alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], after 2 yr of treatment in cotton and soybeans.

In laboratory experiments, plant extracts of small everlasting (Antennaria microphylla Rydb.), field pussytoes (A. neglecta Greene), and leafy spurge (Euphorbia esula L.) were toxic to germinating seeds. Extracts of small everlasting inhibited vegetative development of leafy spurge, and soil taken from the immediate vicinity of roots inhibited germination and radicle elongation of germinating seeds of some species. Small everlasting competes vigorously with leafy spurge, and this competition cannot be attributed to morphology and growth habit. It suppressed vegetative growth of leafy spurge from rhizome sections in which the two species were competing in pots. In field experiments, this shallow-rooted, lowgrowing plant exhibited a marked inhibition on the growth of the vigorous, deep-rooted perennial, leafy spurge, as did the soil in which small everlasting had been growing. Antibiotic competition appears to be significant with the Antennaria spp., and the paucity of forbs in patches of leafy spurge, even when bare ground is visible between shoots, suggests that this species also exerts antibiotic effects on other plants. Allelopathy is probably a significant influence in interspacial relationships of species in most plant communities. A fuller knowledge of these relationships and their causes could lead to the utilization of this phenomenon in weed control.

The butyl ester of fluazifop {[(±)-2-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy)propanoic acid} at 0.26 μM in nutrient solution inhibited root growth of hydroponically grown goosegrass (Eleusine indica Gaertn. ♯ ELEIN), large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA], and giant foxtail (Setaria faberi Herrm. ♯ SETFA). Treating the soil and plant foliage at 0.035 or 0.07 kg ai/ha did not result in greater phytotoxicity than exposing only the foliage of each grass to the herbicide. Foliar-applied fluazifop was retained on the foliage in similar amounts by each of the species. Translocation of 14C to all plant parts was detected 6 h after foliar application of the butyl ester of 14C-fluazifop to the grasses in the pretillering or tillering stage. The majority (90%) of 14C absorbed by each of the species remained in the treated leaf. In hydroponic studies, each species exuded 14C into nutrient solution following foliar application of the 14C-labeled herbicide. The exuded material was predominantly fluazifop with small amounts of compounds more polar than the butyl ester of fluazifop. Uptake and translocation studies suggest that the greater sensitivity of goosegrass to fluazifop may be related to higher concentrations of the herbicide present in plant tissue.

The objective of this research was to develop a model to predict common cocklebur seedling emergence in spring tillage and no-spring-tillage systems in the presence and absence of a soybean canopy. A Weibull function was used to accumulate heat units (i.e., growing degree days) at a 2.5 cm soil depth on days when mean soil temperature, soil water potential, and soil thermal fluctuation were above established thresholds. The base temperature, soil water potential, and soil thermal fluctuation thresholds used for model development were 17 C, −100 kPa, and 7.5 C, respectively. A single function adequately described common cocklebur seedling emergence in the presence and absence of drill-seeded soybean from data combined over an artificial (2004) and natural seedbank (2005) (R2 = 0.986). Model parameterization differed between the artificial and natural seedbank in the absence of spring tillage, but emergence was adequately described, regardless of soybean presence. Separate parameter estimates for the artificial and natural seedbanks were needed to adequately describe emergence in the system without spring tillage (R2 = 0.975 to 0.984). The ability of the model to account for reduced emergence when soil moisture is limited or when daily thermal fluctuation requirements are not met could assist practitioners with assessments associated with field scouting for weeds as well as other management decisions.

The herbicide, 2,6-dichlorobenzonitrile (dichlobenil), applied to the soil surface at 2 lb/A controlled dodder (Cuscuta spp.) and other weeds for 4 to 6 weeks in the field, and did not injure established alfalfa (Medicago sativa L.) significantly. Soil incorporation increased the herbicidal effect of dichlobenil on alfalfa and dodder, but alfalfa injury was increased more than dodder control. Dichlobenil was effective when applied just before sprinkler irrigation, or on moist soil after irrigating. In the greenhouse, dichlobenil vapors moved from a wettable powder formulation mixed with moist soil or from granules on the surface of moist soil, and killed dodder in adjacent untreated soil.

Rates of dissipation, control of troublesome aquatic weeds, and toxicity to fish by the disodium and dipotassium salts of 7-oxabicyclo(2,2,1)-heptane-2,3-dicarboxylic acid (endothall) in farm reservoirs and in growth pools were studied from 1964 to 1967. In 4 out of 14 reservoir applications, initial concentrations of 0.3 to 1.4 ppm dissipated to near the limit of detection in 8 to 20 days. In the other 10, the dissipation ranged from 23 to an increase of 160% in 12 days. The average dissipation was 71%. In growth pools, initial concentrations of 0.5 to 4.0 ppm of endothal dissipated to 0.26 to 2.5 ppm in 12 days.