In studies conducted from 1991 through 1994, researchers investigated the effects of several crop rotations and herbicide programs on crop yield and populations of common lambsquarters, common ragweed, Amaranthus spp., and jimsonweed at two sites. Crop rotations included continuous corn, continuous soybean, corn–soybean, and corn–tomato–soybean, and herbicide programs were the split-plots and included continuous use of acetolactate synthase (ALS)–inhibitor herbicides, continuous use of non–ALS-inhibitor herbicides, annual rotations between ALS- and non–ALS-inhibitor herbicides, combinations of ALS- and non–ALS-inhibitor herbicides in the same year, and no herbicide. Weed control and weed populations generally were affected by an interaction between crop rotations and herbicide programs. After 4 yr, common lambsquarters control was lowest, and populations were highest where fomesafen was used alone for four consecutive years or in rotation with other herbicides. Although common ragweed populations were low at site 2, control at both sites was generally lowest from treatments that included only ALS-inhibitor herbicides. Common ragweed populations were highest at site 1 in 1992 and 1993 following continuous applications of ALS-inhibitor herbicides. Jimsonweed populations were also low at site 2, but control at site 1 in tomato was low. Jimsonweed control from fomesafen and the combination of butylate plus atrazine in soybean and corn, respectively, was variable. Amaranthus spp. populations decreased as the study progressed, and in 1993, control was over 90% from all treatments, except in the case of the treatment combining butylate plus atrazine. Corn and soybean yields varied with year and site, and yields of these crops and tomato were related to rainfall and weed control.

Enhanced foliar injury was obtained with sprays containing the herbicide linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and the insecticide carbaryl (napthyl-N-methylcarbamate) in tolerant carrot (Daucus carota L. ‘Chantenay’). Synergism occurred when the compounds were applied as tank mixes or applied at 1 day intervals. The photosynthetic rate of parsnip (Pastinacea sativa L. ‘Hollow Crown’) leaf discs exposed to both chemicals was greatly reduced when compared to tissues receiving linuron or carbaryl alone. Carbaryl enhanced the penetration of 14C-linuron into intact carrot leaves and parsnip leaf discs. The rate of linuron metabolism was also decreased in the presence of carbaryl. Both of these factors may contribute to the enhanced toxicity obtained with this combination of pesticides.

Feasibility of supercritical CO2 fluid extraction of imazaquin from spiked soil (3.21 μmol kg-1) as an alternative to a conventional extraction method was investigated. The supercritical fluid extraction method involved single-step extraction of herbicide from soil with no further sample cleanup procedures. Extraction parameters were optimized for maximum herbicide recovery. Adding water as a modifier to air-dried soil significantly improved herbicide recovery. Extracting a 1-g soil sample with supercritical CO2 at 0.80 g ml-1 density and 3 ml min-1 flow rate, 80 C extraction temperature, 6 min static extraction followed by 25 min dynamic extraction, and analyte trap temperature of 40 C was optimum for maximum herbicide recovery. When optimum supercritical fluid extraction conditions were used, imazaquin recovery from three texturally different soils ranged from 55 to 64%, which was comparable to a conventional extraction method (63%). The supercritical fluid extraction method consumed 4 ml methanol and 75 ml supercritical CO2 and took approximately 1 h for sample extraction.

Sweet corn is planted over a long season to temporally extend the perishable supply of ears for fresh and processing markets. Most growers' fields have weeds persisting to harvest (hereafter called residual weeds), and evidence suggests the crop's ability to endure competitive stress from residual weeds (i.e., crop tolerance) is not constant over the planting season. Field studies were conducted to characterize changes in the residual weed community over the long planting season and determine the extent to which planting date influences crop tolerance to weed interference in growth and yield traits. Total weed density at harvest was similar across five planting dates from mid-April to early-July; however, some changes in composition of species common to the midwestern United States were observed. Production of viable weed seed within the relatively short growth period of individual sweet corn plantings showed weed seedbank additions are influenced by species and planting date. Crop tolerances in growth and yield were variable in the mid-April and both May plantings, and the crop was least affected by weed interference in the mid-June and early-July planting dates. As the planting season progressed from late-May to early-July, sweet corn accounted for a great proportion of the total crop–weed biomass. Based on results from Illinois, a risk management perspective to weeds should recognize the significance of planting date on sweet corn competitive ability. This work suggests risk of yield loss from weed control failure is lower in late-season sweet corn plantings (June and July) than earlier plantings (April and May).

In greenhouse studies, control of common ragweed (Ambrosia artemisiifolia L. ♯ AMBEL) and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE) was achieved whether or not soybeans [Glycine max L. (Merr.) ‘Ransom’] partially shielded the weeds from foliar applications of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}. Excellent control (> 90%) of common ragweed was obtained in the greenhouse 2 and 4 weeks after plant emergence. Best control (> 90%) of common cocklebur was obtained 2 weeks after plant emergence. A simulated rainfall of 0.6 cm occurring 1 min after acifluorfen application did not decrease control or fresh weight of common ragweed in greenhouse studies. The weed control efficiency of acifluorfen on common cocklebur was reduced when the herbicide was applied intermittently within 6 h of the 0.6-cm simulated rainfall. The weed control efficiency of acifluorfen on both weed species was also reduced when the herbicide was applied intermittently within 6 to 12 h of a 1.3-cm simulated rainfall in greenhouse studies. In field studies, 2.5 cm of simulated rainfall within 12 to 24 h after acifluorfen application reduced control of common ragweed.

Seeds of honey mesquite (Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell) were germinated and grown in aqueous solutions of the sodium salt of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) or the potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram). Elongation of germinating seedling hypocotyls and roots was progressively inhibited by increasing concn of each herbicide up to about 1 or 2 mg/L the first 2 days. After 5 and 10 days, progressively more inhibition occurred at 5 to 10 mg/L of 2,4,5-T and 1 to 2 mg/L of picloram. Four-month-old honey mesquite seedlings were treated with foliar sprays of the 2-ethylhexyl ester of 2,4,5-T or the potassium salt of picloram. Both herbicides caused curling of the stem tip, death of the growing point, cracking below the leaf, and increased numbers of lateral roots. Both herbicides caused phellem cells to enlarge radially, inner cortext and phloem parenchyma to proliferate, and xylem vessels to lignify without enlarging. Starch granules disappeared from treated plants within 8 days and re-occurred in treated plants only 53 days after spraying. Picloram was slightly more toxic to honey mesquite seedlings than 2,4,5-T.

Red rice (Oryza sativa L. # ORYSA) control in soybeans [Glycine max (L.) Merr.] was 93% or more with shallow-incorporated alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] at 3.9 kg ai/ha, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 2.8 kg ai/ha, and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] at 1.7 kg ai/ha. Junglerice [Echinochloa colonum (L.) Link. # ECHCO] control was 80% with alachlor but 90% or more with metolachlor and trifluralin when applied at the same rates. Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 560, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy]phenoxy]propanoic acid} at 280, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} at 140, and mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} plus bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4 (3H)-one 2,2-dioxide] at 140 plus 840 g ai/ha applied postemergence on two- to four-leaf red rice provided at least 87% control. Junglerice control with these treatments was 85% or more with the exception of fluazifop and mefluidide plus bentazon.

Over a 3-yr period the placement of weeds in relation to cotton (Gossypium hirsutum L.) plants greatly influenced the seed cotton yields. After 3-yr of competition the cotton with no weeds yielded about 2300 kg/ha. With weeds confined to between-the-rows placement, yields were about 850 kg/ha. When weeds were confined to in-the-row placement, the cotton was completely shaded and produced no yield. After 3-yr of intense competition throughout each entire growing season no statistical differences were demonstrated between the competitiveness of large crabgrass [Digitaria sanguinalis (L.) Scop.], spurred anoda [Anoda cristata (L.) Schlecht.], prickly sida (Sida spinosa L.) and velvetleaf (Abutilon theophrasti Medic.) to cotton.

The influence of various factors on the tolerance of corn and selected weed species to thifensulfuron was studied in greenhouse experiments. Corn fresh weight was reduced by postemergence application of thifensulfuron when applied at 180 g ai ha−1 without surfactant or at 18 g ha−1 with a nonionic surfactant. Corn was more susceptible to root exposure whereas velvetleaf was more susceptible to foliar exposure. Velvetleaf was most susceptible when plants were young, when a nonionic surfactant was added, and at 20 rather than 30 C. Simulated rainfall 8 h after application reduced velvetleaf injury by thifensulfuron at 18 g ha−1 without surfactant; however, with addition of a nonionic surfactant, velvetleaf injury was reduced only if rainfall occurred less than 2 h after application. Soil moisture level did not affect velvetleaf susceptibility.

Formulations of Fusarium oxysporum Schlechtend:Fr. f.sp. erythroxyli isolate EN-4, pathogenic to Erythroxylum coca var. coca (coca) were evaluated in greenhouse and field studies to determine their relative ability to enhance pathogen populations in the soil or cause disease in coca. The formulations rice-alginate prill, Pesta, and C6 were most thoroughly tested and are products of three formulation processes. The formulations were applied in the greenhouse and field at 33.6 kg ha−1. All the formulations tested enhanced the population of EN-4 in the soil during greenhouse (> 6 wk) and field (> 7 mo) experiments. EN-4 was present in the upper 1 cm of formulation-treated soil at > 200-fold higher populations than established below a depth of 7 to 10 cm in both greenhouse and field experiments. This population distribution was maintained throughout the 7-mo sampling period for field experiments. The enhanced soil populations of EN-4 were associated with an increase in root colonization by the pathogen EN-4 in the field 5 to 7 mo after treatment. The formulated F. oxysporum began to have a significant effect on plant death 100 to 200 d after application in two of three field experiments, based on repeated measures analysis. The various formulations tested tended to establish similar pathogen populations in soil and subsequently caused similar levels of disease. The primary factors influencing formulation performance may be environmental, since inoculum production is dependent on sporulation of the formulation, which, although rapid, may continue over several weeks subsequent to application.

The effect of calcium and nitrogen level on the uptake of linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] from nutrient solution by soybean [Glycine max (L.) Merr.] seedlings was determined and related to root membrane fatty acid composition. Calcium levels in the nutrient solution were 0.4, 4.0, or 8.0 mM and nitrogen levels were 4.0, 16.0, or 32.0 mM with the pH adjusted to 6.5. As calcium concentration increased, linuron uptake decreased. The reverse was true for nitrogen. These changes were not related to transpiration. Increasing calcium concentration increased palmitic acid and decreased linolenic acid in the plasmalemma of the soybean roots resulting in a greater degree of saturation. Nitrogen likewise increased the degree of saturation in the plasmalemma, but the effect was mainly seen in the balance between stearic and linoleic acids. In the mitochondria, however, the trends were inconclusive. High levels of linolenic acid were observed in the mitochondria regardless of treatment.

Benefin accumulated rapidly in the roots of tobacco (Nicotiana tabacum L. ‘Kentucky 14′) seedlings incubated in nutrient solution containing 14C-labeled benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) and remained in the roots unaltered. Very low levels of radioactivity were detected in the shoots. Diphenamid (N,N-dimethyl-2,2-diphenylacetamide) accumulated in the shoots of treated plants throughout the treatment period but remained at low levels in the roots. Diphenamid was extensively metabolized in the shoots but only to a slight extent in the roots. The carbon-14 of pebulate (S-propyl butylethylthiocarbamate) accumulated in moderate amounts in both the roots and shoots of the tobacco seedlings, but attempts to recover pebulate failed.

Field experiments were conducted in Thessaloniki, Greece, from 1991 to 1994 to study the competition of littleseed canarygrass and short-spiked canarygrass biotypes in wheat and to evaluate their response to diclofop, fenoxaprop, tralkoxydim, and CGA-184927. Competitive ability of all canarygrass biotypes was similar, though species differed in panicle numbers. All littleseed canarygrass biotypes showed faster growth rate than the short-spiked canarygrass biotypes. Wheat grain yield decreased as canarygrass density increased. For example, 152 and 304 canarygrass plants m–2 reduced wheat yield 32 and 42%, respectively. None of the canarygrass biotypes at any density had any effect on grain yield of wheat when cold and dry weather prevailed during the early stages of growth. CGA-184927 and tralkoxydim were more effective herbicides against all short-spiked canarygrass biotypes than fenoxaprop and diclofop. CGA-184927 and fenoxaprop provided > 98% control of all littleseed canarygrass biotypes; control with tralkoxydim was < 80%; and diclofop gave 82 to 96% control of this weed species. Herbicide control of canarygrass increased wheat yield relative to the weedy control, and only diclofop was phytotoxic to wheat.

False cleavers and catchweed bedstraw are problematic weeds of field crops in high-latitude regions of the northern Great Plains of North America. The abundance of these species has been increasing in areas of greater tillage intensity and frequency. Field experiments were established over 4 site-yr in Manitoba, Canada, and results indicated that the recruitment of false cleavers and catchweed bedstraw was strongly promoted by a single shallow tillage operation with a sweep cultivator in the spring. Percent recruitment levels in 2001 (pooled over sites) were 17 and 46% for the untilled and tilled treatments, respectively. In 2002, the percent recruitment levels for the untilled and tilled treatments, respectively, were 28 and 38% for the Komarno site and 13 and 28% for the Petersfield site. Only a few and minor differences in microsite conditions (soil temperature, soil moisture, and bulk density) resulted from the single spring tillage pass. The single tillage pass caused a significant relocation of simulated seeds (plastic beads) to below the soil surface and deeper into the soil profile (2–4 cm). Mean bulk density and volumetric soil moisture increased significantly with soil depth. The results of this study suggest that the positive effect of tillage on cleavers recruitment was not due to the effect of tillage on microsite conditions per se. Rather, the vertical redistribution of seed by tillage moved these seeds to a place in which the microsite conditions differed from those on the surface and were more favorable for recruitment. False cleavers and catchweed bedstraw recruitment is clearly promoted by tillage (even minor tillage) under field conditions, and farmers might be able to limit recruitment by limiting spring tillage.

Field and greenhouse studies were conducted to evaluate the responses of several imidazolinone (IMI)-resistant Amaranthus hybridus populations to various acetolactate synthase (EC 4.1.3.18)-inhibiting herbicides. In 1996 field studies, IMI resistance was confirmed in one A. hybridus population (R4) that was not cross-resistant to the sulfonylurea herbicides CGA-277476, chlorimuron, or thifensulfuron. Amaranthus hybridus control with triazolopyrimidine herbicides was ≤ 35%, but control with cloransulam-methyl or flumetsulam plus cloransulam-methyl was higher than with IMI herbicides. Follow-up greenhouse studies were conducted in 1997 and 1998 to investigate the response of one IMI-susceptible (S) A. hybridus population collected near Painter, VA, and four IMI-resistant A. hybridus populations (R1, R2, R3, R4) collected from fields in Somerset County, MD, to postemergence imazethapyr, chlorimuron, thifensulfuron, pyrithiobac, and cloransulam-methyl applications. Resistance to imazethapyr was confirmed in all R populations, and no practical level of cross-resistance to chlorimuron, thifensulfuron, pyrithiobac, or cloransulam-methyl was detected. Based on resistance ratios, R populations were slightly more tolerant to chlorimuron and slightly more sensitive to pyrithiobac, thifensulfuron, and cloransulam-methyl than the S population.

The volatile compounds of crofton weed infested by cotton aphids and sprayed with MeJA were collected and analyzed by the TCT-GC/MS technique. The healthy weeds were controls. Seventeen volatiles identified from crofton weed included green leaf odors, monoterpenes and sequiterpenes, and oxo-compounds. Camphene, 2-carene, α-phellandrene, ρ-cymene, and caryophyllene were the major volatiles and constituted about 77% of the total volatile emissions from the control. In the aphid-infested weeds, no new induced component was found. Among the terpenes, ρ-cymene increased markedly in the infested weeds compared with the control, whereas all sesquiterpenes decreased markedly. Levels of endogenous JA in leaves and young stems of the aphid-infested weeds were markedly higher than in the control, whereas both endogenous SA level and ABA level were not significantly different. MeJA sprayed on crofton weed with the aphid infestation had a similar effect on volatile emissions. It is suggested that JA was one of the most important signals in crofton weed and could regulate the emission of volatile compounds.

Fifty corn poppy populations originating from three counties of northern Greece were evaluated for resistance to tribenuron. Twelve of the populations (six sampled from cereal fields and six from margins) were sampled from the county of Thessaloniki, 15 (13 sampled from wheat fields and two from margins) from Kilkis, and 23 (21 sampled from cereal fields and two from margins) from Serres. Fifty, 39, and 95% of the populations sampled from winter wheat fields originating from Thessaloniki, Kilkis, and Serres were resistant (R), respectively. However, all populations sampled from margins of the same areas were susceptible (S). All populations examined were susceptible to 2,4-D and bromoxynil. The level of resistance to tribenuron varied among populations with the herbicide dose required to reduce growth by 50% (GR50) ranging from 41 g ha−1 (R/S, resistance ratio 137) for the least resistant to over 720 g ha−1 (R/S greater than 2,400) for the most resistant populations. Fresh weight accumulation, seed production, and capsule number of eight R populations grown under field conditions were similar to those recorded for eight S populations originating from sites with high proximity of their respective R populations. However, the estimated mean growth rate (MGR) indicated significant differences due to the resistance trait and the population's origin. In particular, the R populations that originating from Thessaloniki and Serres had MGR 1.3 to 4.3 times lower than the respective S populations, whereas the R populations from Kilkis had similar or higher MGR values compared to the respective S populations. The populations with the highest R/S (greater than 2,400) had low MGR values, and the populations with R/S ranging from 1,437 to 2,227 had high MGR values.

Absorption coefficient (k), infinite reflectance (Ri), and scattering coefficient (s) were tabulated for five wavelengths and analyzed for statistical differences for seven weed species. The wavelengths were: 0.55 μm, 0.65 μm, 0.85 μm, 1.65 μm, and 2.20 μm. The Ri of common lambsquarters (Chenopodium album L.), johnsongrass [Sorghum halepense (L.) Pers.], and annual sowthistle (Sonchus oleraceus L.) leaves at the 0.85-μm wavelength were significantly (p = 0.05) higher than for sunflower (Helianthus annuus L.), ragweed parthenium (Parthenium hysterophorus L.), or London rocket (Sisymbrium irio L.). Annual sowthistle had the largest k value, and Palmer amaranth (Amaranthus palmeri S. Wats.) had the smallest k value at the 0.65-μm chlorophyll absorption wavelength. In general, johnsongrass, ragweed parthenium, or London rocket had the largest s values among the five wavelengths, whereas annual sowthistle and Palmer amaranth were usually lowest.

The time course of diphenamid (N,N-dimethyl-2,2-diphenylacetamide) metabolism in tomato (Lycopersicon esculentum Mill. ‘Sheyenne’) was altered by fumigation with 30 pphm (parts per hundred million) of O3. After 2 days 70% of the absorbed diphenamid was metabolized in controls compared with 83% in fumigated plants. Concentrations of N-methyl-2,2-diphenylacetamide (MMDA) were equivalent in both fumigated and control plants. Less glucoside conjugate (MDAG) was present in fumigated plants 2 to 4 days after treatment than in the control plants. Gentiobioside conjugate (MDAGB) increased rapidly in fumigated plants after 0.5 day but not in control plants until after 2 days. Loss of diphenamid from aerated solution was demonstrated. A scheme for diphenamid metabolism is proposed.

A bioassay standard curve injury rating, using cucumbers (Cucumis sativus L.) as the indicator plant, was developed for quantitatively determining soil residues of 5-bromo-3-sec-butyl-6-methyluracil (bromacil), 6-dichloro-o-anisic acid (dicamba), 3(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), (2,3,6-trichlorophenyl)-acetic acid (fenac), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 2,4-bis(isopropylamino)-6-methoxy-s-triazine (prometone). The herbicide concentrations ranged from 0.001 to 2.187 ppmw. The presence of all the herbicides could be detected at 0.009 ppmw and the herbicides killed cucumbers at 2.187 ppmw. Cucumbers could be used to effectively measure a greater concentration range of fenac than the other herbicides. A highly significant negative correlation existed between injury rating and fresh plant weight. However, concentrations of the herbicides were more easily detected by a visual injury rating on abnormal growth characteristics than by fresh plant weight.