Effects of soil water and herbicide vapors on the phytotoxicity of eight dinitroaniline herbicides to oats (Avena sativa L. ‘Dal’) were studied. Oat primary root length was inhibited more by the herbicides than was shoot length or shoot fresh weight. All of the herbicides, except oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), inhibited primary root length through vapor activity. Vapors of dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) were most inhibitory. Herbicide vapor inhibition increased with temperature. Soil water affected oryzalin activity more than it did that of the other herbicides. Oryzalin phytotoxicity to the oat primary root was reduced more at the low soil water than was that of the other herbicides. Its low vapor activity apparently reduced its effectiveness in dry soil. Difference in magnitude of herbicide phytotoxicity between two soil moisture levels generally was more pronounced at lower herbicide concentration.

Glycine max cultivars exhibit differential tolerance to soil-applied sulfentrazone. The intent of this study was to determine the physiological basis for this differential tolerance by evaluating sulfentrazone absorption and metabolism during the earliest stages of G. max development (i.e., germinating seeds, and germinal seedlings). Imbibed seeds (24 h) of the sulfentrazone-tolerant cultivar ‘Stonewall’ absorbed 37% less sulfentrazone than the sulfentrazone-sensitive cultivar ‘Asgrow 6785’. Similarly, germinal seedlings (i.e., 60 h from start of imbibition) of the sulfentrazone-tolerant cultivars Stonewall and ‘Pioneer 9593’ absorbed 22% less sulfentrazone than the sulfentrazone-sensitive cultivars Asgrow 6785 and ‘Carver’ when exposed to sulfentrazone-containing solution for either 24 or 48 h. The amount of root-absorbed 14C-sulfentrazone that was translocated into cotyledon or hypocotyl tissues did not exceed 11% of the amount absorbed and was similar for all four cultivars. Sulfentrazone metabolism by both imbibed seeds and by germinal seedlings was independent of cultivar. Increasing the sulfentrazone concentration in the seed imbibition solution and increasing the temperature resulted in greater seedling height reduction at 10 d in Asgrow 6758 than in Stonewall. Results indicate that differential absorption during the earliest stages of development is the basis for the differential response among G. max cultivars. Comparatively limited sulfentrazone absorption by Stonewall, as reflected in acceptable seedling injury, remained relatively consistent across the range of concentrations and temperatures evaluated.

Common groundsel is an important weed of strawberry and other horticultural crops. Few herbicides are registered for common groundsel control in such crops, and understanding and predicting the timing and extent of common groundsel emergence might facilitate its management. We developed simple emergence models on the basis of soil thermal time and soil hydrothermal time and validate them with the use of field-derived data from Minnesota and Ohio. Soil thermal time did not predict the timing and extent of seedling emergence as well as hydrothermal time. Soil hydrothermal time, adjusted for shading effects caused by straw mulch in strawberry, greatly improved the accuracy of seedling emergence predictions. Although common groundsel generally emerges from sites at or near the soil surface, the hydrothermal model better predicts emergence when using hydrothermal time at 5 cm rather than 0.005 cm, probably because of the volatility of soil temperature and water potential near the soil surface.

A segment of the debate surrounding the commercialization of genetically engineered (GE) crops, such as glyphosate-resistant (GR) crops, focuses on the theory that implementation of these traits is an extension of the intensification of agriculture that will further erode the biodiversity of agricultural landscapes. A large field-scale study was conducted in 2006 in the United States on 156 different field sites with a minimum 3-yr history of GR corn, cotton, or soybean in the cropping system. The impact of cropping system, crop rotation, frequency of using the GR crop trait, and several categorical variables on emerged weed density and diversity was analyzed. Species richness, evenness, Shannon's H′, proportion of forbs, erect growth habit, and C3 species diversity were all greater in agricultural sites that lacked crop rotation or were in a continuous GR crop system. Rotating between two GR crops (e.g., corn and soybean) or rotating to a non-GR crop resulted in less weed diversity than a continuous GR crop. The composition of the weed flora was more strongly related to location (geography) than any other parameter. The diversity of weed flora in agricultural sites with a history of GR crop production can be influenced by several factors relating to the specific method in which the GR trait is integrated (cropping system, crop rotation, GR trait rotation), the specific weed species, and the geographical location. The finding that fields with continuous GR crops demonstrated greater weed diversity is contrary to arguments opposing the use of GE crops. These results justify further research to clarify the complexities of crops grown with herbicide-resistance traits, or more broadly, GE crops, to provide a more complete characterization of their culture and local adaptation.

Uptake and translocation of 6,7-dihydrodipyrido[1,2-a:2′, 1′-c]pyrazidiinium salt (diquat) in elodea (Elodea canadensis Michx) was investigated by autoradiography and counting of plants treated with diquat-14C. Uptake initially was very rapid followed by a slower accumulation of diquat. Part of this uptake was reversible in water and rapidly reached a saturation value while the slower uptake was nonreversible. This reversibility of uptake appears to indicate an initial passive adsorption probably followed by accumulation. Slight basipetal and acropetal movement of diquat was demonstrated with accumulation in the nodes and axillary buds. Movement was unaffected by light versus dark treatments. Diquat injured treated and adjacent untreated shoots of elodea to almost the same extent. This transfer occurred whether or not the treated and untreated shoots were in contact.

Most previous research on changes in weed abundance and community composition in cropping systems has focused on field crops. The study presented here examined changes in the weed seedbank and aboveground biomass in four organic vegetable cropping systems over a 10-yr period. The systems included an Intensive system with six crops per 4-yr rotation, an Intermediate system with one cash crop per year, a Bio-extensive system with alternating cash crop and tilled fallow years plus prevention of seed rain, and a Ridge-tillage system with one cash crop per year. Systems also differed in the types and number of cover crops between cash crops. During the course of the experiment, the weed community shifted from one dominated by summer annual broadleaf species that reproduce at the end of their lives to a community dominated by summer and winter annuals that mature rapidly. This shift in community composition can be attributed to the change in land use from conventionally managed corn (Zea mays L.) and alfalfa (Medicago sativa L.) to organic vegetable production. In particular, crop rotations with diverse preplantings and postharvest tillage dates interrupted the life cycle of common lambsquarters (Chenopodium album L.) and pigweed species (Amaranthus spp.: mostly Powell amaranth [Amaranthus powellii S. Watson], with small numbers of redroot pigweed [Amaranthus retroflexus L.] and smooth pigweed [Amaranthus hybridus L.]), while favoring a diverse assemblage of quickly maturing species. The study thus demonstrates that an appropriate crop rotation can control the seedbank of weeds like C. album that potentially persist well in the soil. The Ridge-tillage system greatly reduced the frequency and depth of tillage relative to other systems while effectively suppressing perennial weeds. The early-reproducing annuals, however, became more abundant in the Ridge-tillage system than in the other systems, primarily due to escapes along the edge of the scraped ridges. The tilled fallow periods coupled with prevention of seed rain in the Bio-extensive system substantially reduced weed abundance through time and relative to the other systems.

A Palmer amaranth (Amaranthus palmeri S. Watson) population (KCTR: KS Conservation Tillage Resistant) collected from a conservation tillage field was confirmed with resistance to herbicides targeting at least six sites of action, including 2,4-D. The objectives of this research were using KCTR A. palmeri to investigate (1) the level of 2,4-D resistance, (2) 2,4-D absorption and translocation profiles, (3) the rate of 2,4-D metabolism compared with 2,4-D–tolerant wheat (Triticum aestivum L.), and (4) the possible role of cytochrome P450s (P450s) in mediating resistance. Dose–response experiments were conducted to assess the level of 2,4-D resistance in KCTR compared with susceptible plants, KSS (KS 2,4-D susceptible) and MSS (MS 2,4-D susceptible). KSS, MSS, and KCTR plants were treated with [14C]2,4-D to determine absorption, translocation, and metabolic patterns. Additionally, whole-plant dose–response assays were conducted by treating KCTR and KSS plants with P450 inhibitors (malathion, piperonyl butoxide [PBO]) before 2,4-D application. Dose–response experiments indicated a 6- to 11-fold 2,4-D resistance in KCTR compared with susceptible plants. No difference was found in percent [14C]2,4-D absorption among the populations. However, 10% less and 3 times slower translocation of [14C]2,4-D was found in KCTR compared with susceptible plants. Importantly, [14C]2,4-D was metabolized faster in KCTR than susceptible plants. At 24, 48, and 72 h after treatment (HAT), KCTR metabolized ∼20% to 30% more [14C]2,4-D than susceptible plants. KCTR plants and wheat generated metabolites with similar polarity. Nonetheless, at 24 HAT, ∼70% of [14C]2,4-D was metabolized in wheat, compared with only 30% in KCTR A. palmeri. Application of malathion before 2,4-D increased the sensitivity to 2,4-D in KCTR, suggesting involvement of P450s in mediating 2,4-D metabolism. However, no such impact of PBO was documented. Overall, this study confirms that enhanced metabolism is the primary mechanism of 2,4-D resistance in KCTR.

A procedure has been described for the partial purification of the simazine-resistance factor of Zea. The relative solubilities in various solvents and some of the chemical properties of this factor have been studied. Pyridine and hydroxylamine were also found to bring about the conversion of simazine-C14 to the 2–hydroxy analogue. Based on these substances as models, a mechanism has been proposed for the dechlorination of simazine in Zea.

Field studies were conducted in 1977 and 1978 to compare the efficacy of the starch xanthate and activated-sludge polymer controlled-release herbicide formulations with the emulsifiable-concentrate formulations. As incorporation was delayed from immediately to never incorporated, starch xanthate and sludge polymer thiocarbamate herbicide formulations had activity equal to that of the emulsifiable concentrates at our initial and final rating dates. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine)-starch xanthate in 1977 had increased activity over that of the emulsifiable concentrate as incorporation was delayed, as indicated by initial and final visual rating. Starch xanthate did not greatly increase the residual activity of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], or several thiocarbamate herbicides. Starch xanthate formulations of EPTC (S-ethyl dipropylthiocarbamate) and vernolate (S-propyl dipropylthiocarbamate) provided significantly less protection to corn than did addition of the protectant R-29148 [3-(dichloroacetyl)-2,2,5-trimethyloxazolidine]. The sludge polymer formulation had no controlled-release properties.

The addition of 0.5 and 5.0 ppmw of 7-oxabicyclo [2.2.1] = heptane-2,3-dicarboxylic acid (endothall) to solutions of copper sulfate pentahydrate (CSP) at 1.0 ppmw of copper applied to the roots of emersed parrotfeather (Myriophyllum brasiliense (Camb.) increased the copper content of the roots of these plants. Growth of parrotfeather was inhibited by root applications of 0.5 and 5.0 ppmw of endothall, but CSP did not increase its phytotoxicity. However, a synergistic effect, as determined by dry weight, was calculated after treatment of hydrilla (Hydrilla verticillata Casp.) with a combination of 5.0 ppmw of endothall plus CSP at 1.0 ppmw of copper. An increase in copper uptake and a reduction in phosphorus levels was associated with those plants treated with the combination.

The effects of time, concentration, pH, temperature, and metabolic inhibitors on 4-amino-3,5,6-trichloropicolinic acid (picloram) uptake from nutrient solution by oats (Avena sativa L. ‘Markton’) and soybeans (Glycine max L. ‘Lee’) were studied. Oats and soybeans had similar absorption patterns of rapid initial uptake. However, total accumulation patterns markedly differed in that accumulation was concentration-dependent for oats but not for soybeans. Initial uptake by oats and soybean roots increased as solution concentration increased. Picloram was redistributed in oats and soybeans and some egress from roots to solution occurred. Picloram uptake by both plant species was markedly diminished with an increase in pH from 3.5 to 4.5, but pH had little effect from 4.5 to 9.5. Less picloram was taken up by oats and soybean roots from solution maintained at 4 C than at 26 C. Translocation to tops followed a similar trend. Increasing concentrations of three metabolic inhibitors, 2,4-dinitrophenol (DNP), sodium azide, and sodium arsenite, reduced root uptake of picloram in both species. All inhibitors (except DNP for oats) at 10−6 to 10−5 molar concentrations stimulated translocation of picloram to oats and soybean tops while higher concentrations depressed translocation.

Soil residue levels were studied to a depth of 2.4 m for a period of 2 years after application of 1.12 kg/ha of 4-amino-3,5,6-trichloropicolinic acid (picloram). Thirty days after application 93 ppb were recovered in the top 15 cm of soil. Residues were less than 5 ppb at depths of 46 to 122 cm. Six months after application, residues were between 5 and 10 ppb down to 183 cm and less than 5 ppb between 198 and 244 cm. Residues to depths of 244 cm were less than 5 ppb 1 year after treatment. Residue levels to similar depths were studied in two soil types for a period of 1 year after application of conventional and polymerized picloram sprays and granules (3.4 kg/ha of picloram). Conventional sprays resulted in significantly higher soil residues for the sampling period than polymerized sprays. Residues from polymer granules were likewise significantly greater than from polymer sprays. Conventional and polymer formulations were identical with respect to movement through the soil.

Ten commercial soybean [Glycine max (L.) Merr.] cultivars were evaluated for reaction to over-the-top applications of two rates of 3′,4′-dichloropropionanilide (propanil) at the growth stage when three nodes on the main stem had completely unrolled leaves. Propanil, a herbicide commonly applied to rice [Oryza sativa L.] for control of grass weeds, was applied at 0.56 and 3.36 kg/ha; the higher rate is commonly used for control of weeds in rice. ‘Davis’, ‘Hood’, and ‘York’ soybean cultivars were damaged more by propanil than ‘Hill’, ‘Lee’, ‘Lee 68’, ‘Pickett’, ‘Semmes’, ‘Bragg’, or ‘Dare’ when damage was measured by reductions in seed yield and stand and by leaf injury.

Jointed goatgrass is an important weed of wheat in the United States and other parts of the world. Under field conditions, wheat and jointed goatgrass can hybridize and produce backcross derivatives, a situation that may allow gene flow between these two species. In order to gain a better understanding of the factors governing gene flow, a study to characterize patterns of mating between these two species was undertaken. Chloroplast and nuclear microsatellite markers were used to evaluate the parentage of 413 first-generation backcross (BC1) seeds obtained from 127 wheat–jointed goatgrass F1 hybrids, produced naturally under field conditions. Of the 127 hybrids evaluated, 109 (85.8%) had jointed goatgrass as the female parent, whereas the remaining 18 F1 plants (14.2%) had wheat as the female parent. Of the 413 BC1 plants analyzed, 358 (86.7%) had wheat and 24 (5.8%) had jointed goatgrass as the male backcross parent. The male parentage of 31 BC1 (7.5%) plants could not be determined. Under natural field conditions, wheat was the prevalent pollen donor for the production of hybrids and first-generation backcross derivatives. However, hybrids and backcrosses with jointed goatgrass as the male parent also were observed. Thus, the establishment and persistence of a zone of hybridization between these species would result in the development of jointed goatgrass carrying wheat genes.

The compound N-(l,l-dimethylpropynyl)-3,5-dichlorobenzamide affected the development of quackgrass (Agropyron repens (L.) Beauv.) by inhibiting the growth of meristematic regions. The nodes at the apex of treated rhizomes became swollen and necrotic and exhibited increases in DNA, RNA, and protein over untreated rhizomes. These changes in the terminal nodes were accompanied by a dramatic increase in the levels of cellulase and by several disruptive changes in the meristematic, nodal, and internodal tissue of quackgrass rhizomes.

The following herbicides were evaluated for relative phytotoxicity to cotton (Gossypium hirsutum L. ‘Acala SJ-1′), purple nutsedge (Cyperus rotundus L.), and yellow nutsedge (Cyperus esculentus L.) under greenhouse conditions: 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor); 2-chloro-2′,6′-diethyl-N-(butoxymethyl)acetanilide (CP-53619); 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (VCS-438); 4-chloro-5-(dimethylamino)-2-α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone (San-6706); 2-(α naphthoxy)-N,N-diethyl-propionamide (R-7465); and S-isopropyl 5-ethyl-2-methyl-piperidine-1-carbiothioate (R-12001). Herbicides were incorporated 6.35 cm deep, at rates of 1.12, 2.24, and 4.48 kg/ha, into a fine sandy loam prior to planting. All treatments except the low rate of alachlor and VCS-438 controlled yellow nutsedge for 8 weeks. R-7465 and R-12001 at 1.12 kg/ha and San-6706 at 2.24 kg/ha controlled purple nutsedge for 8 weeks. Alachlor and CP-53619 were somewhat less effective against purple nutsedge than yellow nutsedge, but their intermediate rates suppressed purple nutsedge for 4 weeks. Even the high rate of VCS-438 was ineffective against purple nutsedge. Cotton, in terms of fresh shoot weight, exhibited considerable tolerance to 1.12 and 2.24 kg/ha of VCS-438 and CP-53619 and 1.12 kg/ha of R-7465. Applications of 2.24 kg/ha of CP-53619 and 1.12 kg/ha of R-7465, however, suppressed the development of lateral roots of cotton. Other rates of these herbicides and all rates of alachlor, R-12001, and San-6706 moderately to severely injured cotton in most of the experiments.

The combined influence of plant competition and defoliation on development of Canada thistle was investigated in a 2-yr field study. Plant competition was induced by seeding tall fescue and crown vetch. Artificial defoliation was used to simulate various levels of leaf removal by insects. Both defoliation and induced competition reduced biomass of Canada thistle but their impact varied with environmental conditions. Defoliation had a greater detrimental influence than induced competition on thistle biomass in a dry year when growth of the plant competitors was suppressed. In a wet year, induced competition was more important in suppressing Canada thistle than defoliation, and moderate levels of defoliation (25%), applied once when the thistles were 12 to 15 cm in diam, stimulated root weight within the top 20 cm of soil. Reduction in thistle biomass increased with level of defoliation and was greatest when defoliation was applied repeatedly at 14-d intervals in the presence of induced competition. Crown vetch showed very little growth in one season and tall fescue was the primary source of competition for the thistles. The results confirm the hypothesis that combined stresses can substantially reduce biomass development of Canada thistle plants.

Degradation of SAN 6706 [4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] and SAN 9789 [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone] was studied in a sandy loam soil at temperatures of 5, 20, and 35 C. After 210 days of incubation 10, 80, and 97% of SAN 6706 had been dissipated from soil at 5, 20, and 35 C., respectively. SAN 6706 was converted to SAN 9789 and a demethylated metabolite in the soil. SAN 9789 was converted to the demethylated metabolite. It was difficult to differentiate between first and second-order kinetics in the degradation of these compounds. SAN 6706, at 20 and 35 C, had a half life of 50 and 9 days respectively, and an Arrhenius activation energy of 15.8 Kcal/mole. SAN 9789, at 20 and 35 C, had a half life of 270 and 70 days, respectively, and an activation energy of 11.8 Kcal/mole. The degradation of SAN 6706 was inhibited by a chloroform treatment, and microbiological degradation is suggested.

A column leaching study was conducted in a greenhouse to determine the movement of atrazine and alachlor through soil as affected by alfalfa roots in three stages of decay. Alfalfa was grown in soil columns for 6 months and then killed with glyphosate. The 14C-atrazine and 14C-alachlor were applied to soil columns with bromide following 2, 13, or 26 weeks of root decomposition. Most of the herbicide remained in the top 9 cm of soil. However, atrazine and alachlor soil distribution profiles indicated greater preferential movement in columns with roots than in columns without roots. Higher levels of atrazine and alachlor were bound to soil at lower depths in the presence of roots than without roots. Adsorption of atrazine and alachlor on soil with and without alfalfa roots was not significantly different as determined by Freundlich adsorption isotherms. Degradation rates for atrazine and alachlor were not substantially different between soil with and without roots. Although only small amounts of the applied herbicide leached through the columns, preferential flow of herbicides through root-mediated soil macropores and cracks could be a mechanism of herbicide transport through soil under appropriate conditions.

The phytotoxicity of glyphosate [N-(phosphonomethyl) glycine] on seeds (protected or non-protected with soil) and seedlings of Italian ryegrass (Lolium multiflorum Lam.) and red clover (Trifolium pratense L.) was studied in the greenhouse. Percent germination of Italian ryegrass seeds covered with soil was significantly reduced with glyphosate applied at 4 kg/ha. The direct treatment over the seeds on the soil surface was more toxic, reducing the number of established seedlings at dosages of 3 and 4 kg/ha. In the two red clover seed treatments, germination was significantly reduced with 2 kg/ha of herbicide. Even though germination was reduced at intermediate rates of glyphosate, shoot growth and tillering were improved and yields of dry weight were equivalent to that of untreated plants. Postemergence applications of glyphosate were phytotoxic to both species with the effects becoming more pronounced at increasing dosages. However, at equal dosage, red clover was less susceptible than Italian ryegrass. The patterns of foliar absorption and translocation of 14C from 14C-glyphosate was similar in Italian ryegrass and red clover. 14C was translocated throughout the plants and exhibited apoplastic and symplastic movement.