Benghal dayflower is an exotic weed species in the United States that is a challenge to manage in agricultural fields. Research was conducted in North Carolina, Georgia, and Florida to evaluate the longevity of buried Benghal dayflower seeds. Seeds were buried in the field for 2 to 60 mo at a depth of 20 cm in mesh bags containing soil native to each area. In North Carolina, decline of Benghal dayflower seed viability was described by a sigmoidal regression model, with seed size having no effect on viability. Seed viability at the initiation of the study was 81%. After burial, viability declined to 51% after 24 mo, 27% after 36 mo, and < 1% after 42 mo. In Georgia, initial seed viability averaged 86% and declined to 63 and 33% at 12 and 24 mo, respectively. Burial of 36 mo or longer reduced seed viability to < 2%. The relationship between Benghal dayflower seed viability and burial time was described by a sigmoidal regression model. In Florida, there was greater variability in Benghal dayflower seed viability than there was at the other locations. Seed viability at the first sampling date after 2 mo of burial was 63%. Although there were fluctuations during the first 24 mo, the regression model indicated approximately 60% of seed remained viable. After 34 mo of burial, seed viability was reduced to 46% and then rapidly fell to 7% at 39 mo, which was consistent with the decrease in seed viability at the other locations. Although there is a physical dormancy imposed by the seed coat of Benghal dayflower, which has been detected in previous studies, it appears that a decline in buried seed viability to minimal levels occurs within 39 to 48 mo in the southeastern United States, suggesting that management programs must prevent seed production for at least four growing seasons to severely reduce the Benghal dayflower soil seedbank.

Wild radish (Raphanus raphanistrum L.) is a weed found globally in agricultural systems. The facultative winter annual nature of this plant and high genetic variability makes modeling its growth and phenology difficult. In the present study, R. raphanistrum natural seedbanks exhibited a biphasic pattern of emergence, with emergence peaks occurring in both fall and spring. Traditional sigmoidal models were inadequate to fit this pattern, regardless of the predictive environmental variable, and a corresponding biphasic model (sigmoidal + Weibull) was used to describe emergence based on the best parameters. Each best-fit chronological, thermal, and hydrothermal model accounted for at least 85% of the variation of the validation data. Observations on phenology progression from four cohorts were used to create a common model that described all cohorts adequately. Different phenological stages were described using chronological, thermal, hydrothermal, daylength-dependent thermal time, and daylength-dependent hydrothermal time. Integrating daylength and temperature into the models was important for predicting reproductive stages of R. raphanistrum.

Microbial metabolites have been identified as a promising class of natural herbicides due to their effective control against weeds and a relatively low environmental impact. Here we report on the potency and crop safety of a natural compound with herbicidal properties, the metabolite SPRI-70014 from Streptomyces griseolus CGMCC 1370. The compound showed excellent herbicidal activities on various broadleaf and gramineous weeds in both greenhouse and field trials. In germination inhibition experiments, SPRI-70014 inhibited the emergence of both root and shoot at 1 mg L−1. At a dose of 31.3 g ai ha−1, SPRI-70014 provided effective control over most broadleaf weeds in greenhouse trials. Observations on absorption and translocation using a cucumber plant model system indicated that SPRI-70014 could be absorbed by the root but only partly by the stem. Field trials showed that SPRI-70014 provided effective control over most weed species tested at a dose of 1,000 g ai ha−1. Crop safety experiments showed that the compound had no harmful effect on peanut or wheat plants at doses up to 2,000 g ai ha−1. These results indicated that this compound could be developed as a potential POST herbicide for control of broadleaf weeds in peanut and wheat fields.

Isopropyl N-(3-chlorophenyl)carbamate (CIPC), 2-chloroallyl diethyldithiocarbamate (CDEC), ethyl N,N-di-n-propylthiolcarbamate (EPTC), sodium 2,4-dichlorophenoxyethyl sulfate (sesone), and N-1-naphthylphthalamic acid (NPA) controlled Amaranthus palmeri S. Wats., (Palmer amaranth) Echinochloa colonum (L.) Link, (junglerice) and Sorghum vulgare Pers. var. sudanense Hitchc. (sudangrass) more efficiently when applications were followed by overhead irrigation, except in a few instances where weeds were controlled regardless of the irrigation method. More CIPC, sesone, CDEC, and EPTC penetrated below ¼ inch into soils, and they penetrated deeper with overhead irrigation.

Tissue abnormalities in colonial bentgrass (Agrostis tenuis Sibth.) were observed after foliage applications at normal doses of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-(2, 4, 5-trichlorophenoxy)propionic acid (silvex), or 4-(2,4-dichlorophenoxy)-butyric acid [4-(2,4-DB)]. They included proliferations of the pericycle, hypertrophic cortical cells, and massed lateral root and root hair formations. The abnormalities usually resulting from phenoxy rates of 1, 1-½, or 3 pounds active per acre were often followed by death of the bentgrass within 20 days after treatment.

Although a number of physiological effects of amitrole (3–amino–1,2,4–triazole) on plants have been reported there appears to be nothing in the literature on its effect on germination and seedling development in cotton.

Recently sodium trichloroacetate (TCA) has come to the front as a useful herbicide for the control of annual or perennial grasses. The object of this paper is to report the persistence of the chemical in different types of soils as related to time and rates of applications.

A crop rotation of sorghum [Sorghum bicolor (L.) Moench] and soybeans [Glycine max (L.) Merr.] with various weed control treatments was conducted from 1968 to 1975 at Lincoln, Nebraska, in order to improve weed control in these two crops. Poor weed control during one growing season increased weed growth and decreased yields of succeeding crops. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 1.1 kg/ha on soybeans showed greater soil carryover toxicity to sorghum planted 12 months later than did atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 3.4 kg/ha on sorghum to subsequently planted soybeans. Under this crop rotation green foxtail [Setaria viridis (L.) Beauv.], tall waterhemp [Amaranthus tuberculatos (Moq.) J. Sauer], and large crabgrass [Digitaria sanguinalis (L.) Scop.] decreased; whereas, velvetleaf (Abutilon theophrasti Medic), sunflower (Helianthus annuus L.), and Pennsylvania smartweed (Polygonum pensylvanicum L.) increased. Germinating weed seedlings from soil samples were greater in weedy check plots during the final years of the crop rotation due to a buildup of seed from those species that increased. Handweeding, herbicides, and plowing reduced weed populations, weed competition, and increased sorghum and soybean yields.

Bromacil (5-bromo-3-sec-butyl-6-methyluracil) was much more effective in killing post oak (Quercus stellata Wangenh.) and blackjack oak (Q. marilandica Muenchh.) trees than 4-amino-3,5,6-trichloropicolinic acid (picloram) when applied to soil at 5.6 and 11.2 kg/ha in spots, bands, or by broadcasting. When applied at 5.6 kg/ha in bands or broadcast, picloram effected better crown reduction than bromacil on mockernut hickory (Carya tomentosa Nutt). Differences between rates and methods of applying bromacil were small. While bromacil was superior on the prevalent overstory species, post oak and blackjack oak, picloram excelled on the most numerous understory plants.

Weeds remain the foremost production challenge for organic small grain farmers in the northeastern United States. Instead of crops sown in narrow, single-line rows, band sowing offers a more uniform spatial arrangement of the crop, maximizing interspecific while reducing intraspecific competition. Weeds in the inter-band zone are controlled by cultivating with aggressive sweeps; tine harrowing can target weeds in both intra- and inter-band zones. Field experiments in Maine and Vermont in 2016 and 2017 evaluated band sowing for improved weed control, crop yield, and grain quality in organic spring barley (Hordeum vulgare L. ‘Newdale’). Specifically, we compared: (1) the standard practice of sowing 16.5-cm rows at a target crop density of 325 plants m−2, (2) narrow-row sowing with increased crop density, (3) wide-row sowing with interrow hoeing, and (4) band sowing both with and (5) without inter-band hoeing. Mustard (Sinapis alba L. ‘Ida Gold’) was planted throughout the experiment as a surrogate weed. Compared with the standard practice, band sowing with hoeing reduced surrogate weed density on average by 45% across site-years. However, effects on weed biomass and yield were inconsistent, perhaps due to suboptimal timing of hoeing and adverse weather conditions. In 1 out of 4 site-years, band sowing with hoeing reduced surrogate weed biomass by 67% and increased crop yield compared with the standard treatment. Results also indicate that band sowing with hoeing may improve 1,000-kernel weight and plump kernel grain-quality parameters.

Glasshouse experiments were conducted to determine the phytotoxic effect of triallate [S-(2,3,3-trichloroallyl)-diisopropylthiocarbamate] granules on oat (Avena sativa L. ‘Kelsey’). The sphere-of-influence of the granules was found to diminish rapidly with increase in the horizontal distance from the tips of the caryopses. At a distance of 10 mm from the caryopsis tip there was no significant effect on the growth of the oat seedling. The need for the granules to be in close proximity to the developing coleoptile could not be counteracted by increasing the number of granules per caryopsis once the granules were 10 mm or more from the caryopsis. These results give cause to seriously question the generally held belief that triallate disperses through the soil in a volatile phase. Extension of the first leaf and mesocotyl was inhibited much more readily by triallate than coleoptile extension, which was stimulated by a number of treatments. When granules were left on the soil surface of sub-irrigated pots the phytotoxic effect seemed to be mediated through triallate-exposure of the coleoptile tip.

High herbicide costs and uncertainty about annual weed control at planting have limited adoption of no-till spring wheat production systems in the northern Great Plains. Chlorsulfuron, metsulfuron, and CGA-131036 at 10 to 20 g ai ha–1 plus nonionic surfactant generally controlled both emerged kochia and wild mustard equally well (>80%) whether or not combined with glyphosate at 250 g ha–1 plus nonionic surfactant. In two of three trials persistent phytotoxic residues of these sulfonylurea herbicides in soil controlled both weeds better in midseason and early summer 1 yr after treatment than did glyphosate, which has only foliar activity. While the absolute net returns of different treatments varied among herbicides, relative net returns were insensitive to changes in either herbicide or wheat price. Herbicide use tended to boost net returns for no-till spring wheat in years with good weather but depressed net returns in a drought year. Chlorsulfuron at 10 and 20 g ha–1 increased net returns in all three trials. Metsulfuron and combinations of either metsulfuron or chlorsulfuron with glyphosate had variable effects on net returns.

The activity of α-amylase in barley (Hordeum vulgare L. ‘Wong’) half-seeds, induced by exogenous gibberellic acid (GA), was almost completely inhibited by 5 × 10−4M commercial formulations of (2,3,6-trichlorophenyl)acetic acid (fenac), 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil), and 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid (endothall). At the same concentration, 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) caused severe inhibition (72%); 2,2-dichloropropionic acid (dalapon) was intermediate (42%); and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), 2-(4-chloro-6-ethylamino-s-triazin-2-ylamino)-2-methylpropionitrile (SD 15418), and 2% solvent dimethylsulfoxide (DMSO) were only slightly inhibitory to GA-induced α-amylase production.

Empirical models of crop–weed competition are integral components of bioeconomic models, which depend on predictions of the impact of weeds on crop yields to make cost-effective weed management recommendations. Selection of the best empirical model for a specific crop–weed system is not straightforward, however. We used information–theoretic criteria to identify the model that best describes barley yield based on data from barley–wild oat competition experiments conducted at three locations in Montana over 2 yr. Each experiment consisted of a complete addition series arranged as a randomized complete block design with three replications. Barley was planted at 0, 0.5, 1, and 2 times the locally recommended seeding rate. Wild oat was planted at target infestation densities of 0, 10, 40, 160, and 400 plants m−2. Twenty-five candidate yield models were used to describe the data from each location and year using maximum likelihood estimation. Based on Akaike's Information Criterion (AIC), a second-order small-sample version of AIC (AICc), and the Bayesian Information Criterion (BIC), most data sets supported yield models with crop density (Dc), weed density (Dw), and the relative time of emergence of the two species (T) as variables, indicating that all variables affected barley yield in most locations. AIC, AICc, and BIC selected identical best models for all but one data set. In contrast, the Information Complexity criterion, ICOMP, generally selected simpler best models with fewer parameters. For data pooled over years and locations, AIC, AICc, and BIC strongly supported a single best model with variables Dc, Dw, T, and a functional form specifying both intraspecific and interspecific competition. ICOMP selected a simpler model with Dc and Dw only, and a functional form specifying interspecific, but no intraspecific, competition. The information–theoretic approach offers a rigorous, objective method for choosing crop yield and yield loss equations for bioeconomic models.

An application of potassium nitrate or urea to the soil of detopped potted tomato plants [Lycopersicon esculentum Mill.] increased the rate of exudation from the stumps of the plants from 100 to over 300% and increased the concentration of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine [atrazine] in this augmented exudate from 9 to 40%. Atrazine applied to the soil at 2:00 PM was detected in the stump exudate within 10 min and with an application of 3500 μg per pot it was approaching its maximum concentration by the end of 3 hr. The build-up in the concentration of atrazine in the exudate occurred at a faster rate in plants treated with potassium nitrate than in water control plants. Increasing the soil temperature from 10 to 30 C increased the rate of exudation and at each temperature an application of potassium nitrate or of urea increased the concentration of atrazine in the augmented exudate. In addition to atrazine, 2-chloro-4,6-bis(isopropylamino)-s-triazine [propazine], 2-methoxy-4,6-bis(isopropylamino)-s-triazine [prometone], and 2-methoxy-4-ethylamino-6-isopropylamino-s-triazine [atratone] were applied at 1750 and 3500 μg/pot. The concentration of these triazines in the exudate increased directly with their solubility in water. An application of urea increased the concentration of all four triazines in the exudate.

Uptake and translocation of 14C-buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} in corn (Zea mays L.) and redroot pigweed (Amaranthus retroflexus L.) were studied following both foliar and root treatments under greenhouse and growth chamber environments. Following foliar application, 14C-buthidazole was absorbed by the leaves of corn and redroot pigweed seedlings in similar amounts. Translocation occurred only toward the tip of the treated leaves in corn, whereas in redroot pigweed the 14C moved both acropetally and basipetally. Rapid uptake by the roots and rapid movement to the leaves via the xylem seems to be the main pathway of uptake and translocation of 14C-buthidazole supplied to the roots of redroot pigweed plants. Uptake by both the roots and the emerging coleoptile and transport to the foliage seems to be the pattern of absorption and translocation of buthidazole in corn following preemergence application. Differences in absorption did not appear to be an important factor contributing to selectivity of buthidazole between corn and redroot pigweed. However, translocation of 14C-buthidazole supplied to the roots was faster to the redroot pigweed shoots than to corn shoots.

Induction of germination in dormant barnyardgrass seeds by wounding was investigated. Previous research indicated that a volatile compound was emitted during imbibition of wounded caryopses. When wounded caryopses were submerged in agar, total germination and speed of germination were stimulated, and the stimulation was dependent upon the concentration of agar. A twofold increase in germination occurred in 1% agar versus water, and a fivefold increase with caryopses placed in 5% agar. When wounded caryopses were imbibed, there was a fourfold increase in respiration over that of intact caryopses after 1 h. This increased rate of respiration of wounded caryopses continued for 7 h, while there was a gradual increase in respiration of intact caryopses. Carbon dioxide induced intact dormant caryopses to germinate but was not effective in stimulating germination of the seed (spikelet). High levels of abscisic acid found in the hulls of dormant seeds may have prevented the action of carbon dioxide. These results suggest that increased respiration resulting from wounding provides elevated levels of carbon dioxide in the microenvironment of the seed, thus stimulating germination. Removal of the hulls is necessary for germination even in high levels of carbon dioxide.

Copper-containing herbicides are often applied to control photoautotrophic populations to reduce biosynthesis of the earthy odorant geosmin. The objective of this investigation was to determine the effects of copper-containing herbicides on geosmin and biomass biosynthesis by heterotrophic cultures of the bacterium Streptomyces tendae and the fungus Penicillium expansum. Cultures of S. tendae treated with 12.7 mg Cu L−1 (copper sulfate) accumulated 44.6% more biomass and the mycelium contained five-fold greater concentrations of geosmin than controls. Additionally, P. expansum cultures exposed to 12.7 mg Cu L−1 (copper sulfate) accumulated 9.2% more biomass and 18-fold greater concentrations of geosmin than controls. Cultures of P. expansum and S. tendae, treated with copper chloride, copper-ethylenediamine complex, and copper chelate also accumulated more geosmin and biomass than controls. Inductively coupled plasma atomic emission spectrometry of S. tendae of untreated control cultures indicated that cellular copper concentrations were below 0.5 mg Cu kg−1. However, S. tendae cells grown on a medium containing 5 mg Cu L−1 copper sulfate contained 12.88 ± 0.54 mg Cu kg−1, suggesting that cellular accumulation of copper may be associated with increased geosmin biosynthesis. If field microbial populations exhibit similar responses to copper, copper-algicide application may contribute to geosmin-induced “off-flavors” under certain circumstances.

The effects of MT-101 and its herbicidally active form, NOP, on the germination and seedling growth of hemp sesbania and rice were investigated. MT-101 decreased the germination of hemp sesbania by 57 and 90% at 0.05 and 0.5 mM, respectively, 1 d after treatment (DAT) in petri dishes. The germination, however, recovered such that there was no significant difference between treatments 4 to 6 DAT. NOP completely inhibited the germination of hemp sesbania at both 0.05 and 0.5 mM 1 DAT. However, germination also similarly recovered, and there was no difference between treatments 4 to 6 DAT. Neither MT-101 nor NOP decreased the germination of rice 3 to 6 DAT. In greenhouse trials preemergence (PRE) application of MT-101 at 2.25 kg ai ha−1 decreased the density (number of plants pot−1), plant height, and dry weight of hemp sesbania by 85, 67, and 91%, respectively. When applied postemergence (POST), MT-101 at 2.25 kg ha−1 decreased the density, plant height, and dry weight by a maximum of 58, 61, and 82%, respectively, indicating that MT-101 may have greater activity when applied PRE. NOP had greater activity than MT-101 on hemp sesbania. NOP at 2.25 kg ai ha−1 decreased the density, plant height, and dry weight of hemp sesbania 99, 78, and 97%, respectively, with PRE application. A POST application of NOP at 2.25 kg ha−1 decreased the dry weight of hemp sesbania 91 to 94%. A PRE application of NOP at 2.25 kg ha−1 decreased the dry weight of rice by 58%. Rice was not affected by POST applications of MT-101 but was affected slightly by NOP. These results suggest that MT-101 is a possible weed control agent in rice.

Bromoxynil efficacy, uptake, translocation, and spray retention were investigated when bromoxynil was applied in conventional water volumes of 234 L ha−1 and in simulated sprinkler irrigation at 127 000 L ha−1 to common lambsquarters. Bromoxynil controlled common lambsquarters similarly regardless of water volume, whereas injury to spearmint, a tolerant crop, was greatest using low water volume. Spray retention was 18 and 38 times greater on common lambsquarters and spearmint, respectively, when bromoxynil was applied in 234 L ha−1 than 127 000 L ha−1. Two weeks after applying bromoxynil in 127 000 L ha−1 water volume, common lambsquarters dry weight was 60% of the nontreated check where only soil was treated but was 5% of the nontreated check where only leaves were treated. Roots of lambsquarters absorbed 22% of 14C-bromoxynil applied to hydroponic solution by 7 d, but only 2% was translocated to the shoots. Percent absorption and translocation of foliar-applied 14C-bromoxynil were 15 and 6% greater, respectively, from 0.0096 g L−1 than from a 1.2 g L−1 bromoxynil solution by 24 h after application. Uptake of bromoxynil was 13% greater through lower than upper leaf surfaces. These results suggest efficacy of bromoxynil applied in large spray volumes is, in part, due to root uptake, efficient foliar uptake and translocation, and uptake from lower leaf surfaces.