Adsorption of five phenylurea herbicides, metobromuron [3-(p-bromophenyl)-1-methoxy-1-methylurea], monolinuron [3-(p-chlorophenyl)-1-methoxyl-1-methylurea], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea], and CGA-15646 [3-(3-chloro-4-methylphenyl)-1,1-dimethylurea] by eight selected soils of Czechoslovakia were studied. Constants from Freundlich and Langmuir equations were calculated and correlated with the major soil properties. Freundlich K values ranged from 1.84 to 128, and the Freundlich equation was better fitted to the adsorption isotherms than was the Langmuir equation. Soil organic-matter content was the most important factor influencing the range of adsorption.

Four cropping systems were evaluated from 1975 to 1977 for the control of yellow nutsedge (Cyperus esculentus L.). Crops grown in 1975 and 1976 included alfalfa (Medicago sativa L. ‘Elcamino WL-600′), barley (Hordeum vulgare L. ‘CM-67′), corn (Zea mays L. ‘Dekalb T214′), and cotton (Gossypium hirsutum L. ‘Acala SJ-2′). Herbicides used included butylate (S-ethyl diisobutylthiocarbamate) in corn, EPTC (S-ethyl dipropylthiocarbamate) in alfalfa, glyphosate [N-(phosphonomethyl)glycine] in fallow plots, and MSMA (monosodium methanearsonate) in cotton. Cotton, which was grown continuously as one of the four cropping systems, was the only crop grown in 1977. Based on weed counts, crop yields, and the consistent decline in the number of tubers, all cropping systems provided substantial control of yellow nutsedge each year. Two years of either alfalfa treated with EPTC or double cropping barley with corn treated with butylate preceeding cotton reduced the number of viable yellow nutsedge tubers by 96%. Two years of chemically fallowing plots with glyphosate following barley and preceeding cotton was 98% effective in reducing viable tubers. Treating continuous cotton with MSMA, although somewhat inferior to the above systems, reduced the number of viable nutsedge tubers by 91% in 3 yr.

A primary reason for studying the fate of a herbicide in soil is because of its potential effect, beneficial or detrimental, on plants. Herbicide concentrations in soil often can be accurately analyzed by chemical or physical procedures. But such quantitative measurements sometimes are not well correlated with plant response because of a number of interacting soil and environmental factors. If the question is not “How much herbicide residue is present in the soil?”, but rather “How much potential exists for herbicidal effects on plants?”, then the use of plants as one aspect of studies on herbicide persistence can be valuable. This paper addresses factors influencing the response of plants to herbicide residues under field conditions.

Field research was conducted in 1982 and 1983 to characterize the persistence of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)pyridinone} in five Georgia soils. Fluridone persisted less than 365 days in all soils, with shorter persistence upon reapplication in 1983 which indicated the potential for enhanced microbial degradation. A significantly higher rate of loss in 1983 compared to 1982 was recorded in the Greenville sandy clay and Dothan loamy sand soils. A higher rate of loss was recorded for the 1.7 kg ai/ha than the 0.6 kg/ha treatment in the Bradson clay loam and Rome gravelly clay loam soils. No grain sorghum [Sorghum bicolor (L.) Moench. ‘BR 64’) injury was observed in a field bio assay planted in the spring of 1984. Herbicide leaching did not appear to be an important method of loss.

Fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} controlled annual grasses in cucumbers (Cucumis sativus L. ‘Calypso’ and ‘Poinsett’), cantaloupe (Cucumis melo L. ‘Edisto 47’), zucchini squash (Cucurbita pepo L. ‘Elite’), and sweet potato (Ipomoea batatas L. ‘Jewel’) when applied as single or repeated applications of 0.3 or 0.6 kg ai/ha during 1982 and 1983 in North Carolina. All crops were generally tolerant to fluazifop and yields were equal to cultivated controls in all but one experiment. Residues detected in the various crops by high-performance liquid chromatography (HPLC) decreased as time elapsed between application and harvest increased. Approximately 1 ppm (w/w) of fluazifop was detected in cucumbers at 8 days after application, but residues were below the least detectable limit (0.05 ppm) when cucumbers, squash, and cantaloupe were harvested at 18 to 29 days after application. Fluazifop concentrations were 0.06 ppm or less in sweet potatoes at 55 days after application, and no fluazifop was detected at 84 days after application. Small cucumbers (<12 cm long) had greater fluazifop residues than larger fruit (>12 cm long) 20 days following application.

The activity of foliage applications of N,N-dimethyl-2,2-diphenylacetamide (diphenamid) was greatly enhanced by exposing the plants to high relative humidity for 6 hr immediately after chemical application. Growing plants under low light intensity further increased the activity of diphenamid under these conditions. This response occurred with a number of plant species, including tomato (Lycopersicon esculentum Mill.), Japanese millet (Echinochloa crusgalli (L.) Beauv., var. frumentacea), lettuce (Lactuca sativa L.), and radish (Raphanus sativus L.). Low light, but not high relative humidity, increased the activity of diphenamid as a soil application. Unaltered diphenamid and not its known metabolites seemed to be responsible for the increased activity of foliage sprays under conditions of low light and high relative humidity.

Analysis of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] in soil solution after application of 0.5 or 1.0 ppmw revealed up to five-fold differences among three Alabama soils (Lucedale fine sandy loam, Decatur silty clay loam, and Sacul loam). Differences in fluometuron in soil solution were attributed to variable organic matter present and clay fractions. Fluometuron concentration in soil solution for each soil correlated well with control of four broadleaf weed species in a field experiment.

Greenhouse studies revealed that glyphosate [N-(phosphonomethyl)glycine] at 3.4 kg/ha or picloram (4-amino-3,5,6-trichloropicolinic acid) at 0.3 kg/ha more effectively reduced further growth of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] when treated at a height of 30 cm than did 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 1.1 kg/ha or dicamba (3,6-dichloro-o-anisic acid) at 0.6 kg/ha. Glyphosate or picloram applications were also more effective than 2,4-D or dicamba applications in reducing amount of regrowth that occurred after treated plants were cut at the soil surface. Glyphosate plus 2,4-D, glyphosate plus dicamba, glyphosate plus picloram or 2,4-D plus picloram combinations also effectively reduced further growth of treated plants and subsequent regrowth after plants were initially harvested. Greenhouse studies revealed that glyphosate plus ethephon [(2-chloroethyl)phosphonic acid] at 1.7 plus 0.6 kg/ha or glyphosate plus ammonium sulfate at 1.1 plus 6.7 kg/ha were no more effective than glyphosate alone at 1.7 kg/ha. Dowco 290 (3,6-dichloropicolinic acid) at up to 2.2 kg/ha did not effectively inhibit growth of honeyvine milkweed.

Research was conducted to determine the suitability of the Fermi-Dirac distribution function for modeling the seedling emergence of downy brome, johnsongrass, and round-leaved mallow, as influenced by burial depth. Six sets of previously published emergence data were used to formulate the model and test its adequacy. Two independent johnsongrass emergence data sets were used to validate the model. Constant temperature growth chamber studies were conducted to evaluate the effects of temperature and moisture on the model parameters. The Fermi-Dirac distribution function was found to adequately describe the seedling emergence of downy brome, johnsongrass, and round-leaved mallow as indicated by a good visual data fit, narrow confidence intervals for the model parameters, and regression analysis of observed vs. modeled data. Although this function is a model used in physical science, its parameters can be related to abiotic factors such as soil texture, temperature, and moisture.

The limited understanding of soil nitrogen (N) effects on crop yield loss to weeds prevents the refinement of integrated weed management to consider soil fertility. A 3-yr field experiment compared ammonium nitrate applications before corn emergence (PRE N) or in late June (POST N) on the growth of giant foxtail, velvetleaf, common waterhemp, and grain corn. The N responses were studied in corn population densities of 5.4 and 7.9 plants m−2 to understand how crop density might influence N effects on yield loss. In late June of each year, leaf areas were 25% (corn), 64% (velvetleaf), and 41% (giant foxtail) lower with POST N than with PRE N. Common waterhemp leaf area in late June was unaffected by N timing. Corn population density did not affect weed shoot dry weights evaluated in late June. Corn and velvetleaf heights in late July were up to 19 and 48% lower, respectively, with POST N compared with PRE N. Common waterhemp and giant foxtail heights in late July were unaffected by N timing. Corn yield was decreased 13 to 18% by giant foxtail with POST N compared with PRE N. Velvetleaf seed yield was lower, but giant foxtail seed yield was higher, with POST N than with PRE N. Velvetleaf and giant foxtail seed yields were 23 to 56% and 30 to 62% lower, respectively, with the high corn population density compared with the low population density. In competition between corn and common waterhemp, neither N timing nor corn population affected corn yield loss or common waterhemp seed production. N management may alter weed competitiveness and weed seed production in corn, but fertilization recommendations may vary with the weed species that are present.

Seed from 21 common milkweed (Asclepias syriaca L. # ASCSY) populations from six states were germinated on six substrates (filter paper, sand, peat, clay, and mixtures) under three temperature regimes. The variation in germination response between populations and experimental conditions was analyzed. The greatest percent germination (59% average over all substrates) was obtained with an alternating 20 C (16 h), 30 C (8 h) temperature regime. At a constant temperature of 30 C, germination was lower (32% average) and much more variable among seeds from different populations. At 25 C, average percent germination dropped to 1.2% over all substrates. Germination appeared to be strongly correlated with seed source (population), temperature, and substrate type, and poorly correlated with seed size. No association was found between geographical origin and germination response.

The anatomy of the husk (lemma and palea) and caryopsis coat (pericarp, seed coat or testa, and nucellar epidermis) of a typical mature wild oat (Avena fatua L.) caryopsis was investigated using both scanning electron microscopy and light microscopy. Both the lemma and palea consist of very thick-walled, lignified cells. In section, the lemma appears almost twice as thick as the palea. The pericarp is comprised of only one or two layers of relatively thin-walled cells and is closely appressed to the underlying seed coat over most of the grain. Both the outer seed-coat cuticle and the inner cuticle are present over almost the entire caryopsis and are continuous with the pigment strand that occurs deep in the crease region of the grain. The only discontinuities in the seed coat are at the basal end of the grain near the embryo. In the dorsal region of the caryopsis, the outer cuticle is approximately 3.5 μm in thickness, whereas the inner cuticle is less than 1 μm in thickness. Where the two pass over the embryo they are much thinner, with the inner cuticle becoming almost indistinguishable in places. The remains of the nucellar epidermis are tightly amalgamated to the seed coat and outer tangential walls of the underlying aleurone cells, which are clearly distinguishable by their large size and characteristic appearance.

A new extraction method for the HPLC-UV determination of metsulfuron in soil was developed and compared with NaHCO3 extraction and a lentil bioassay technique. The new procedure consisted of metsulfuron extraction using anion exchange membranes followed by a dichloromethane concentration of the membrane eluates. Three soils representing different landscape positions were spiked with metsulfuron to yield concentrations in the range of 0 to 40 μg kg−1 dry soil and were analyzed by the above procedures. At a given spike rate, the efficiency of the anion exchange membrane extraction was highest for the soil from the upper slope position and lowest for the soil from the lower slope position, indicating that the amount of ion-exchangeable sulfonylurea was affected by soil properties. Similar trends in degree of root growth inhibition were observed for lentil response to metsulfuron presence in soil; percent root growth inhibition was related to the landscape position as the amount of membrane-extractable metsulfuron. The percent shoot growth inhibition was not soil dependent and did not differ among soils. The efficiency of NaHCO3 extraction for metsulfuron did not vary with soil type; in the NaHCO3 method, because of the buffered alkaline nature of the extraction, differences in soil properties, particularly soil pH, would have less effect on metsulfuron recovery. Because of similar trends for the results of the membrane extraction method and a lentil root bioassay, anion exchange membrane extraction may provide useful information on bioavailable fractions of sulfonylurea herbicides in soil.

Field studies were conducted to determine the effect of early-season and early- plus late-season acetolactate synthase–resistant Helianthus annuus interference on Glycine max and H. annuus growth and yield at two sites in Missouri. Helianthus annuus densities of 3 plants m−2 were established shortly after G. max emergence in all plots except the weed-free check. To study early-season interference, H. annuus were removed with postemergence glyphosate (0.84 kg ae ha−1) 2, 4, 6, and 8 wk after planting (WAP) and kept weed-free for the rest of the growing season. Glycine max yields were not different with 2, 4, 6, or 8 wk of early-season interference at either location. To study early- plus late-season interference, H. annuus densities were established at 3 plants m−2. They were then removed 2, 4, 6, or 8 WAP with glyphosate and subsequently reestablished at the same density within 2 wk after removal by newly emerging and transplanted H. annuus. These H. annuus were allowed to remain in the field for the remainder of the growing season. This provided a weed-free period of approximately 2 wk during the growing season beginning 2, 4, 6, or 8 WAP. Season-long interference and no-interference treatments were also included. Glycine max yields were reduced 47 to 72% with season-long interference. Helianthus annuus vegetative dry matter was approximately 56% lower at Columbia than at Miami. Glycine max yields tended to increase as the weed-free period was delayed into the growing season. Early-season weed-free periods (2 to 4 and 4 to 6 WAP) allowed H. annuus to become re-established before G. max formed a canopy and resulted in larger amounts of H. annuus biomass and seed production as well as G. max yield losses of 15 to 80%. Re-establishment of H. annuus in 6 to 8 WAP and 8 to 10 WAP weed-free treatments generally resulted in the plants surviving for only a few weeks after establishment and not producing seed or reducing G. max yield.

Scanning electron microscopy (SEM) showed that EPTC (S-ethyl dipropylthiocarbamate) caused an aggregation of the epicuticular wax layer of corn (Zea mays L.). R-25788 (2,2-dichloro-N,N-diallylacetamide) prevented this aggregation when applied in combination with EPTC. Neither EPTC, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], nor R-25788 changed the weight of chloroform extractable epicuticular wax on corn leaves. EPTC apparently does not block lipid synthesis in corn as it does in other plant species. Thus R-25788 does not protect corn from EPTC or metolachlor by overcoming such a block. EPTC did affect wax arrangement on the leaf surface and caused an increase in the cuticular transpiration of corn and predisposed corn to injury from subsequent postemergence applications of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion). R-25788 protected corn against these deleterious effect.

Three herbicides, amine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid], glyphosate [N-(phosphonomethyl)glycine], and dicamba (3,6-dichloro-o-anisic acid) were applied for field bindweed (Convolvulus arvensis L.) control in grain/summerfallow or grain/legume rotations. After the first year all herbicide retreatments were made using 2,4-D amine. The 2,4-D treatment at 3.4 kg/ha gave 65% field bindweed control. Field bindweed control averaged 17% higher when the 2,4-D was applied in August rather than July. The 3.4-kg/ha rate gave 45% better field bindweed control than the 1.1 kg/ha rate. Dicamba at 6.7 kg/ha gave 90% field bindweed control and glyphosate at 4.5 kg/ha gave 86% control. Dicamba persisted in the soil for 1 to 3 yr after application and caused winter wheat (Triticum aestivum L.) and lentil (Lens culinaris Medik.) yield loss. Crop yields were highest more than 90% of the time from plots treated with 2,4-D or glyphosate.

Preliminary greenhouse studies indicated the presence of a synergistic interaction between low rates of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] or diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] in combination with linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] or chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea]. In a 3-yr field study, moderate injury of cotton (Gossypium hirsutum L. ‘Stoneville 213’) with no yield reduction was observed with fluometuron or diuron at 1.68 and 1.12 kg/ha, respectively, but higher rates (5.04 and 3.36 kg/ha, respectively) caused injury and yield reductions. Soybean [Glycine max (L.) Merr. ‘Hill’] injury ratings during the second year indicated a synergistic interaction between residue from fluometuron at 5.04 kg/ha combined with linuron at 2.48 kg/ha or chlorbromuron at 3.85 kg/ha, and from diuron at 3.36 kg/ha combined with linuron at 2.48 kg/ha. These interactions were not apparent in soybean yield data. Soybean injury the third year ranged from 30 to 60% with single or repeated applications of linuron or chlorbromuron, although yields were not affected. Residual fluometuron and diuron from 2 yr of application at 5.04 and 3.36 kg/ha, respectively, injured soybeans, but did not reduce yields. Significant synergistic interactions were observed through injury and yield measurements after two annual applications of fluometuron at 5.04 kg/ha combined with linuron or chlorbromuron. A synergistic interaction was detected in soybean yields with chlorbromuron at 3.85 kg/ha preceded by two annual applications of diuron at 3.36 kg/ha. Such interactions may occur under field conditions, but are unlikely to be economically significant. Chemical analysis indicated little evidence of accumulation, even with repeated application of fluometuron or diuron at 5.04 and 3.36 kg/ha, respectively.

Field studies were conducted during 1983 and 1984 to determine the single and interactive effects of trifluralin, soybean thrips, and the sodium salt of acifluorfen on soybean. Increased soybean injury was observed in 1983 when acifluorfen at 0.6 kg ai/ha was applied to soybeans infested with soybean thrips versus plants where soybean thrips were controlled. Soybean injury measured by percent defoliation and visual injury ratings was reduced when thrips were controlled versus soybeans where thrips were not controlled with carbaryl at 0.9 kg ai/ha in 1983. Soybean thrips alone did not reduce soybean seed yield in this study. Acifluorfen reduced soybean photosynthetic rate, shoot weight, root weight, and seed yield. Trifluralin had no effect on soybean growth parameters measured in this study.

Napropamide [2-(α-napthoxy)-N,N-diethylpropionamide] inhibited root and shoot growth in corn (Zea mays L. ‘NC+ 59’) and tomato (Lycopersicon esculentum Mill. ‘Niagara VF315’) seedlings. Shoot growth was reduced less than root growth in both species. Corn roots were approximately 10 times more sensitive to napropamide than were tomato roots. Translocation of napropamide from the roots to the shoot of tomato occurred within 0.5 h and followed an apoplastic pattern. Little movement of napropamide from the roots to the shoots occurred in corn. Metabolism of napropamide was not evident in either species during an 8-h exposure. Absorption studies showed that total napropamide levels were 60% higher in corn root tissue than in tomato root tissue. The greater napropamide content in the corn roots was associated with a tightly bound fraction of the total napropamide influx.

Responses of soybeans [Glycine max (L.) Merr. ‘Bragg’] and red rice (Oryza sativa L.) to postemergence applications of mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} and bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] alone and in combinations were evaluated in greenhouse studies. Soybeans were tolerant to bentazon up to the highest tested rate of 2.0 kg/ha, but their height was reduced by mefluidide at 1.0 kg/ha. Soybeans were not injured by any tested combination of the two herbicides. Bentazon applied alone at rates of 5.0 kg/ha and above had a significant effect on red rice injury. Mefluidide applied at rates above 0.25 kg/ha severely reduced height and fresh weight of red rice. When these two herbicides were combined, a synergistic reaction occurred, and the combination was much more effective in controlling red rice than was either herbicide applied alone. The addition of a surfactant significantly increased the activity of the combination on red rice up to 0.25 kg/ha of mefluidide and at all rates of bentazon.