The herbicide 3-amino-2,5-dichlorobenzoic acid (amiben) was converted to N-(3-carboxy-2,5-dichlorophenyl)-glucosylamine, N-glucosyl amiben, in roots of plants treated with amiben. Identification of N-glucosyl amiben was accomplished by means of thin-layer and gas chromatography and confirmed by infrared spectroscopy. The postulated metabolite was synthesized and found to be identical with the product of amiben metabolism in plants.

A greater understanding of the factors that regulate weed seed return to and persistence in the soil seedbank is needed for the management of difficult-to-control herbicide-resistant weeds. Studies were conducted in Tifton, GA to (1) evaluate whether glyphosate resistance, burial depth, and burial duration affect the longevity of Palmer amaranth seeds and (2) estimate the potential postdispersal herbivory of seeds. Palmer amaranth seeds from glyphosate-resistant and glyphosate-susceptible populations were buried in nylon bags at four depths ranging from 1 to 40 cm for intervals ranging between 0 and 36 mo, after which the bags were exhumed and seeds evaluated for viability. There were no detectable differences in seed viability between glyphosate-resistant and glyphosate-susceptible Palmer amaranth seeds, but there was a significant burial time by burial depth interaction. Palmer amaranth seed viability for each of the burial depths declined over time and was described by exponential decay regression models. Seed viability at the initiation of the study was ≥ 96%; after 6 mo of burial, viability declined to 65 to 78%. As burial depth increased, so did Palmer amaranth seed viability. By 36 mo, seed viability ranged from 9% (1-cm depth) to 22% (40-cm depth). To evaluate potential herbivory, seed traps with three levels of exclusion were constructed: (1) no exclusion, (2) rodent exclusion, and (3) rodent and large arthropod exclusion. Each seed trap contained 100 Palmer amaranth seeds and were deployed for 7 d at irregular intervals throughout the year, totaling 27 sample times. There were seasonal differences in seed recovery and differences among type of seed trap exclusion, but no interactions. Seed recovery was lower in the summer and early autumn and higher in the late winter and early spring, which may reflect the seasonal fluctuations in herbivore populations or the availability of other food sources. Seed recovery was greatest (44%) from the most restrictive traps, which only allowed access by small arthropods, such as fire ants. Traps that excluded rodents, but allowed access by small and large arthropods, had 34% seed recovery. In the nonexclusion traps, only 25% of seed were recovered, with evidence of rodent activity around these traps. Despite the physically small seed size, Palmer amaranth is targeted for removal from seed traps by seed herbivores, which could signify a reduction in the overall seed density. To be successful, Palmer amaranth management programs will need to reduce soil seedbank population densities. Future studies need to address factors that enhance the depletion of the soil seedbank and evaluate how these interact with other weed control practices.

Metabolism of C14-labeled and unlabeled atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) was studied in oats, soybeans, and beans (susceptible); cotton and peanuts (intermediate in susceptibility); and Johnsongrass, grain sorghum, and corn (resistant). Atrazine residues were found in all plants 11 days after a preemergence application of 1 lb atrazine/A. Methanol was found to be a better extraction solvent for atrazine and hydroxyatrazine than chloroform. Undegraded atrazine found in plants was roughly correlated with susceptibility, but atrazine absorption was not directly correlated with plant susceptibiliy. Radioactivity remaining in plant residue after methanol extraction likewise was not completely correlated with susceptibility. All plants converted some atrazine to hydroxyatrazine and the amount of hydroxyatrazine formed was somewhat correlated with resistance. The three resistant species converted at least twice as much atrazine to hydroxyatrazine as did the susceptible soybean and oats. Beans converted considerably larger amounts of atrazine than did other susceptible species.

Factors influencing injury to oats from 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) residues in the soil were studied over a period of five years. Initial rate of triazine application was highly important with significant injury in about one-half of the trials on plots treated with 2 lb/A the year prior to planting oats, and on all plots treated at 4 lb/A. No material difference was found on plots treated with equivalent rates of atrazine and simazine. Granular preparations of atrazine left a residue that was more injurious than wettable powders. Disking the seedbed for oats, rather than plowing, resulted in greater injury. Cultivation of the corn between the rows after treatment did not influence the injury the following year. Soil type did not have a marked effect on injury in this study. Above-normal average mean air temperatures appeared to reduce injury the following year in some instances. Experiments initiated in years of abundant rainfall during April to October tended to have less injury the next year than experiments initiated in years when rainfall was limited.

To develop an understanding of how adjuvants might enhance glyphosate [N-(phosphonomethyl)glycine] activity, absorption and translocation of a polyethoxylated tallow amine amphoteric surfactant (MON 0818) were examined in field bindweed (Convolvulus arvensis L. # CONAR). Scanning electron microscopy did not reveal any physical disruption of the epicuticular waxes from spray applications of MON 0818, an oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate) surfactant, or glyphosate. Radioactive MON 0818 absorption was rapid during the first 6 h. Maximum absorption (84%) occurred by 24 h after application. Less than 3% of the applied radioactivity was recovered from the epicuticular wax of treated leaves. Movement of radioactivity away from the treated area was limited predominantly to movement within the treated leaf. Altering light intensity or humidity in which the plants developed before treatment did not influence MON 0818 absorption.

Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations of such species have become common in no-till production fields in the Midwest. This research was conducted to determine the influence of herbicide- and cover-crop-based winter annual weed management systems and crop rotation on winter annual weed growth and seed production, SCN population density, and crop yield. Two crop rotations (continuous soybean and soybean-corn) and six winter annual weed management systems (a nontreated control, fall and spring herbicide applications, spring-applied herbicide, fall-applied herbicide, fall-seeded annual ryegrass, and fall-seeded winter wheat) were evaluated in no-tillage systems from fall 2003 to 2006 at West Lafayette, IN and Vincennes, IN. Fall or spring herbicide treatments generally resulted in lower winter annual weed densities than cover crops. Densities of henbit and purple deadnettle increased over years in the cover crop systems but remained constant in the herbicide systems. Averaged over sites and years, winter annual weed densities were nearly 45% lower in the spring than the fall due to winter mortality. Corn yield was reduced by the cover crops at West Lafayette but not Vincennes. Winter annual weed management system had no influence on soybean yield. SCN population density was reduced by including corn in the crop sequence but was not influenced by winter annual weed management. The density of weedy host species of SCN in the experimental area was relatively low (less than 75 plants m−2) compared to densities that can be observed in production fields. The results of these experiments suggest that inclusion of corn into a cropping sequence is a much more valuable SCN management tool than winter annual weed management. In addition, control of winter annual weeds, specifically for SCN management, may not be warranted in fields with low weed density.

Much research has been conducted on mesotrione activity on crops and weeds, but information is lacking in regards to the relative contribution of soil and foliar absorption of mesotrione. Three experiments conducted at Virginia Tech's Glade Road Research Facility in Blacksburg, VA, evaluated the effects of 50 and 90% relative humidity (RH) on the activity of mesotrione applied to foliage, soil, and soil plus foliage. Tall fescue injury ranged from 0 to 21% and was significant in 6 of 20 comparisons. Three of these injury events were caused by soil plus foliar applications, which were always more injurious than foliar only applications, which were more injurious than soil-only applications. Both application placement and RH significantly influenced smooth crabgrass responses to mesotrione. Smooth crabgrass phytotoxicity was lowest when mesotrione was applied only to foliage and highest when mesotrione was applied to soil and foliage. Increasing RH from 50 to 90% caused a 4- to 18-fold increase in plant phytotoxicity when mesotrione was applied only to foliage. By dissecting the plant canopy, it was noted at 14 d after treatment, when averaged over RH, that white leaves comprise 16% of leaves when only foliage was treated and 55 and 62% when applied to soil plus foliage and soil only, respectively. Furthermore, white tissue was found predominately in the two youngest leaves when mesotrione was applied to soil or both soil and foliage, but in older leaves when applied only to foliage. Data indicate mesotrione entering plants through soil travels quickly to growing points and has an equal or greater effect on plant phytotoxicity than foliar-absorbed mesotrione. In addition, foliar-absorbed mesotrione appears to increase in plants significantly with increasing RH, but does not move rapidly to growing points.

Prior research indicated that analysis of nuclear DNA content by flow cytometry could be used to distinguish smooth pigweed × tall waterhemp hybrids when the parent lines are known. Flow cytometry was performed on nuclei isolated from several Illinois populations of smooth pigweed and tall waterhemp. The smooth pigweed and tall waterhemp analyzed had nonoverlapping 2C nuclear DNA content values, with mean values of 1.04 and 1.34 pg, respectively. The consistent difference in DNA content observed between the two species indicates that DNA content analysis can be used to distinguish their hybrid progeny in natural populations.

Microarray analysis was used to follow changes in gene expression coinciding with seasonal changes in the dormancy status of crown buds of field-grown leafy spurge. Known cold-regulated genes were induced, and numerous gibberellic acid–responsive genes were down-regulated during the transition from paradormancy to endodormancy. Genes involved in photomorphogenesis were induced during endodormancy. Also, ethylene signaling responses were observed during ecodormancy rather than endodormancy. These results provide additional insights into the signals regulating expression of several genes previously associated with transition from paradormancy to growth in root buds.

Economic assessment of weed management strategies in rice is dependent upon a quantitative estimate of the yield impact of a given weed population. To assist rice producers in making such assessments, a mathematical model was developed to predict rice yield reduction as a function of weed density and duration of interference. The nonlinear empirical model was a unique 3-dimensional adaptation of the Richards equation with 4 parameters. Using published data, individual parameter values were fitted for each of 6 weed species interfering with either conventional or semi-dwarf statured rice cultivars. The functional form of the equation produced surfaces that were qualitatively consistent with available data and experience regarding rice-weed biology. Hence, predictions from the model should be useful and reliable in assessing the economic impact of weeds and in determining the feasibility of alternative weed control treatments for various field scenarios.

Studies of the development and distribution of root systems of intraspecific and interspecific competition were conducted between soybean [Glycine max. (L.) Merr. ‘Lee 68′] and tall morningglory [Ipomoea purpurea (L.) Roth]. Tall morningglory at three plant densities and soybean were grown for 2 yr on a Taloka silt loam. The greatest density of soybean and tall morningglory roots grown under intraspecific competition was in the surface 12 cm and in the center of the row. Greater values of root length and density were during the dryer season. The largest fraction of total root length at a given date also was in the surface 12 cm and decreased with depth. The fraction at a given depth was a dynamic property of the root system during the growing season. When compared with the soybean root system, tall morningglory roots were found at deeper depths and had greater root densities. Little expansion of the soybean root system was found after initiation of the soybean reproductive phase. During this phase, the tall morningglory root system was increasing at a faster rate of growth than the soybean root system. The greatest density of roots grown under interspecific competition also was in the surface 12 cm and at the center of the row. These values were less than those found under intraspecific competition. Root distribution and development are dynamic functions of growth stage, planting density, and plant species.

Flucarbazone-sodium, a new herbicide, exhibits high bioactivity at low concentrations. To elucidate potential carryover and crop injury, the behavior of flucarbazone in six Western Canadian soils was studied in the laboratory. A sensitive bioassay was developed for the detection of flucarbazone. Of five crops tested, oriental mustard showed the highest degree of root and shoot inhibition from the presence of flucarbazone in soil. Flucarbazone concentrations as low as 1 μg kg−1 were detected by the mustard root inhibition method. This bioassay was used to examine phytotoxicity and persistence of flucarbazone. Phytotoxicity was related to soil organic carbon content. Concentrations corresponding to 50% inhibition (I 50 values) were estimated after fitting the data to a log-logistic model. I 50 estimates ranged from 6.0 to 27.5 μg kg−1 for soils containing 1.1 to 4.3% organic carbon, respectively, and were correlated (R = 0.979) with percent organic carbon in the investigated soils. Persistence of flucarbazone was examined in soils incubated at 25 C and moisture content of 85% field capacity (FC). Flucarbazone dissipation followed first-order kinetics in one soil, but a two-compartment model provided the best fit for dissipation in the other soils. Half-lives (t0.5), calculated from dissipation curves in each soil, ranged from 6 to 110 d. Half-lives were correlated (R = 0.776) with soil organic carbon. Flucarbazone dissipation was more rapid in soils containing less organic carbon. Flucarbazone was more persistent in drier soil; t0.5 was 11 d in soil at 85% FC and was 25 d in soil at 50% FC. Soil characteristics and environmental conditions will affect the degree of plant injury to sensitive crops the year after flucarbazone application.

Palmleaf morningglory (IPOWR) and pitted morningglory (IPOLA) were compared in field and greenhouse tests under simulated rice field conditions to quantify flood tolerance characteristics of the two species. IPOWR survived a 13-cm flood in the field if the flood was applied 12 days after planting (DAP) or later. In contrast, IPOLA did not survive floods applied before 19 DAP. Only IPOWR survived a 5-cm flood applied 5 DAP in the field. In the greenhouse, both species were unable to emerge from under 1 cm of soil when flooded greater than 1 cm deep. Although both species emerged from water-saturated soil, IPOWR emerged earlier and produced more dry weight than did IPOLA. Emergence from the water surface of 2-cm-tall IPOWR was better than that of IPOLA when submerged in water up to 7 cm deep, and total dry weight (as a percent of a nonflooded control) was two to four times greater for IPOWR. Even a 5-cm flood reduced leaf area, height, dry weight, and photosynthesis of IPOLA more than that of IPOWR. At 20 C and low oxygen (1%), germination percentage of IPOWR was about four times higher than IPOLA. Germination, growth, and certain physiological processes of IPOWR are more tolerant than those of IPOLA to moderately deep floods (and low soil oxygen levels). Thus, IPOWR is potentially a greater weed problem than IPOLA in rice fields. The fact that neither species was capable of emerging from soil under even shallow flood depths helps explain why morningglories are prevalent only in shallow or water-saturated areas on rice field levees.

Medusahead is an invasive annual grass that, once established, severely affects range-land productivity and stability. Medusahead builds large seedbanks in the litter and on the soil surface. Effective weed control of medusahead involves either inhibiting germination from the seedbank, eliminating the seedbank, or enhancing germination so that plants are available for control. The purpose of this study was to determine the influence of nitrogen enrichment, immobilization, and nitrification inhibition treatments in the field on the size and germination status of medusahead seedbanks. The germination status of medusahead seeds in seedbanks was determined by periodically collecting field samples of surface soil and litter and bioassaying them in greenhouse emergence tests. Control seedbanks had increased seedling emergence with KNO3 or GA3 enrichment of the bioassay substrate. The combination of these two materials increased emergence. Nitrogen enrichment increased seedling establishment in the field. Carbon enrichment in the field decreased seedling establishment and increased medusahead seeds in seedbanks. Nitrapyrin treatment decreased medusahead in the field similar to carbon enrichment. In comparison to the control or other treatments, GA3 enrichment was not as effective in increasing emergence from nitrapyrin-treated bioassay samples. The combination of carbon and nitrapyrin treatments was very effective in eliminating medusahead emergence in the field, but in wetter years, it never completely eliminated medusahead seedling recruitment and subsequent reproduction. These treatments have promise for influencing succession in medusahead infestations if an adapted perennial species, capable of competing under low nitrogen levels, becomes available.

Unmodified, cyanoethylated, and crosslinked corn starches were reacted with 2,4-dichlorophenoxyacetyl chloride in pyridine to produce the corresponding 2,4-D [(2,4-dichlorophenoxy)acetic acid]esters of high acyl content. Hydrolysis studies at pH 6 and 8 at ambient temperature showed that these insoluble compositions liberated varying amounts of 2,4-D and soluble 2,4-D esters by ester link and glucoside bond cleavage, respectively, at rates that indicate their possible use as controlled-release herbicides.

Experiments were conducted to determine 14C absorption, translocation, and metabolism by pitted morningglory (Ipomoea lacunosa L. # IPOLA) and ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. # IPOHE] foliarly treated with 14C-acifluorfen [5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-nitrobenzoic acid] or 14C-lactofen [(±)-2-ethoxy-1-methyl-2-oxoethyl-5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-dinitrobenzoate]. Seventy-one to 84% of applied 14 C-acifluorfen was recovered in leaf water wash of ivyleaf morningglory compared to 32 to 46% from pitted morningglory. Sixty-four percent of applied 14C-lactofen was recovered in leaf water wash 96 h after treatment in both morningglory species. Thirty-five to 37% more 14C from applied 14C-acifluorfen was found in pitted morningglory treated leaves than ivyleaf morningglory treated leaves. Less than 28% of applied 14C-lactofen was extracted from treated leaves of either morningglory species. Translocation and metabolism of 14C-acifluorfen and 14C-lactofen were minimal in both morningglory species.

Combinations of 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron) with O,O-diethyl S-2-(ethylthio)-ethyl phosphorodithioate (disulfoton) or O,O-diethyl S-(ethylthiomethyl) phosphorodithioate (phorate) in soil resulted in synergistic phytotoxicities. These synergistic phytotoxicities persisted 21 to 27 weeks in alternately fallow-cropped soils treated with 0 to 12 ppm disulfoton or phorate and 0 to 1.0 ppm diuron where oats (Avena sativa L., var. Mark-ton) was the bioassay plant, and persisted 5 to 15 weeks in alternately fallow-cropped soils treated with 0 to 12 ppm disulfoton or phorate and 0 to 1.33 ppm diuron where corn (Zea mays L., var. US 13) was the bioassay plant. The persistence of the combined pesticides corresponded closely with persistence of the individual pesticides. Corn and cotton (Gossypium hirsutum L., var. Acala 4-42) were more tolerant than was oats to diuron and diuron-insecticide combinations.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, CGA-82725 {2-propynyl 2-[4-[(3,5-dichloro-2-pyridinyl)oxy]phenoxy]propanoate}, RO 13-8895 {acetone-O-[D-2-[p-(α,α,α-trifluoro-p-tolyl)oxy]phenoxy]propionyl oxime}, and difenopenten {4-[4-[4-(trifluoromethyl)phenoxy]phenoxy]-2-pentenoic acid} were evaluated as single and/or split applications for postemergence control of johnsongrass [Sorghum halepense (L.) Pers. ♯ SORHA] grown from rhizomes in soybeans [Glycine max (L.) Merr.]. Good to excellent control, crop safety, and yield enhancement were achieved with all herbicides evaluated. Antagonism between postemergence grass and broadleaf herbicides was evaluated by applying sethoxydim, CGA-82725, RO 13-8895, and difenopenten alone to soybeans infested with johnsongrass grown from seed, and applying these herbicides as mixtures with acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], or benazolin (4-chloro-2-oxobenzothiazolin-3-ylacetic acid). Acifluorfen was most antagonistic to the activity of postemergence grass herbicides, with difenopenten and sethoxydim the most susceptible to antagonism. Reductons in johnsongrass control were attributed to antagonism by broadleaf herbicides, which caused soybean yield reductions of up to 67%.

Naphthaleneacetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D), and 2-chloro-4-ethylamino-6-isopropylamino s-triazine (atrazine) were applied to Chlorella pyrenoidosa in an attempt to characterize mathematically the growth inhibition responses obtained. (Chlorella was found to serve well as a test organism.) Inhibition results induced by NAA and 2,4-D satisfactorily supported the hypothesis inherent in the kinetic interpretation. Results with atrazine were most satisfactorily interpreted by a probit analysis which showed large differences in rate of toxicity between high and low concentrations. This difference is thought to be responsible for the poor fit to a straight line in the reciprocal plots of the kinetic analysis. It is assumed that growth inhibition by atrazine resulted from a blocking of the photosynthetic process.

In considering the interaction between microorganisms and herbicides applied to the soil, two effects may become of great practical significance. One involves the potential inhibition or even germicidal action of the chemical to the microscopic inhabitants of the soil. These organisms, chiefly the bacteria, fungi and actinomycetes, occupy a unique position in biological cycles in terrestrial habitats and are essential for plant growth and soil fertility. The microorganisms decompose root and crop residues, mobilize the reserve of organic nitrogen and phosphorus, carry out transformations involving a change of oxidation state and bring about many other reactions necessary for crop production. Any deleterious influence, even of a temporary nature, could have a profound effect upon crop yields.