Sublethal doses of glyphosate [N-(phosphonomethyl)glycine] applied in a 50-μl drop in the partially furled third true leaf of 30-day-old sorghum [Sorghum bicolor (L.) Moench ‘Tophand’] seedlings induced basal stem swelling and bud release. Combining glyphosate with cycloheximide {3-[2-(3,5-dimethyl-2-oxycyclohexyl)-2-hydroxyethyl]glutarimide}, a cytokinin [N6 (2-isopentenyl)adenine], or L-phenylalanine significantly reduced the incidence of basal stem swelling. No such reductions was observed when indole-3-acetic acid or L-tyrosine was combined with glyphosate. The fresh weights of the seedlings given the combination treatments reflected the effects of glyphosate, except one combination that included tyrosine significantly reduced fresh weight and three combinations that included phenylalanine significantly increased fresh weight.

Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), and clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were applied to honey mesquite (Prosopis glandulosa Torr. # PRCJG) on seven different dates about every 3 weeks from May to September in 1980 and 1981. Concentrations of 2,4,5-T or triclopyr in stem tissue were usually less than 2 μg/g fresh weight regardless of date of application. Concentrations of picloram and clopyralid were as high as 11 and 22 μg/g fresh weight, respectively, in upper stem phloem at some dates of application. Higher concentrations of all herbicides were detected in upper stem phloem than in the upper stem xylem or basal stem phloem or xylem. More herbicide tended to be detected in stems when herbicides were applied early (May and June) than late (August and September) in the season. Concentrations of triclopyr and picloram recovered from honey mesquite stems were about 25% greater at 3 than at 30 days after treatment, whereas concentrations of 2,4,5-T and clopyralid were about 50% greater at 3 than at 30 days after application.

Corn (Zea mays L. ‘DeKalb 640′), kidney beans (Phaseolus vulgaris L. ‘Light red’) and oats (Avena sativa L. ‘Kanota’) were grown in solution culture and the roots exposed to radioactively labeled atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. The radioactivity from 3H-atrazine, or its metabolites, was located in microautoradiographs of corn leaf sections, almost exclusively at the perimeter of the vascular bundles, and was primarily confined to the cell walls and intercellular spaces, with no activity associated with subcellular organelles. Radioactivity from 3H-atrazine in oat leaf section microautoradiographs was primarily associated with the chloroplasts, with no evidence of radioactivity specifically associated with other subcellular organelles. Sucrose density gradient centrifugation of homogenized leaf tissue following exposure of the plants to 14C-atrazine showed that most of the radioactivity was associated with the light cell fragments and cytoplasm for the test species. There was no accumulation of 14C-activity in any of the heavier subcellular organelles from corn leaf cells. A peak of radioactivity was associated with the chloroplast fraction from oat and kidney bean leaves.

Early weed and crop interference was examined in a greenhouse pot experiment combining aspects of additive, substitutive, and diallel designs. Cotton (Gossypium hirsutum L. 'Stoneville 213′) and four weeds {purple nutsedge (Cyperus rotundus L.), large crabgrass [Digitaria sanguinalis (L.) Scop.], velvetleaf (Abutilon theophrasti Medic.) and prickly sida (Sida spinosa L.)} were grown singly and in all possible combinations of pairs including reciprocals for 5 weeks in 10-cm plastic pots. After 5 weeks large crabgrass was the tallest species in all combinations except when grown with purple nutsedge. Purple nutsedge, however, had more leaf area and greater dry weight than all other species. Height, leaf area, and dry weight were lowest in prickly sida. Mean relative yields in mixtures (a measure of competitive ability) were 1.90, 1.15, 1.13, 0.86, and 0.41 for purple nutsedge, large crabgrass, cotton, velvetleaf, and prickly sida, respectively, when grown with the other four species as associates. Conversely, purple nutsedge and cotton as associates depressed mean relative yields of competing species to 0.59 and 0.94. Large crabgrass, velvetleaf, and prickly sida as associates increased mean relative yields of competing species to 1.17, 1.18, and 1.55, respectively. Analysis of these data and replacement-series diagrams indicated that purple nutsedge was the most competitive, prickly sida the least, and the other species were intermediate and approximately equivalent in competitive ability.

The distribution pattern of s-triazine-resistant biotypes of common lambsquarters (Chenopodium album L. #3 CHEAL) and smooth pigweed (Amaranthus hybridus L. # AMACH) in Virginia was determined. Seeds were collected from suspected triazine-resistant biotypes of both species. Triazine resistance was confirmed by measuring chlorophyll fluorescence in the presence of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine]. Greenhouse bioassay with whole-plant material and a sinking leaf disc assay were also performed as further confirmation of triazine resistance. Triazine-resistant smooth pigweed was confirmed in 19 counties and common lambsquarters in eight counties in Virginia. Triazine-resistant smooth pigweed and common lambsquarters were located mostly in the northern and southwestern highlands of the state where there has been a long history of triazine use in no-till corn (Zea mays L.) production. S-triazine-resistant biotypes were also cross-resistant to other representative s-triazine and as-triazine herbicides but susceptible to the substituted urea herbicide diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea].

Bentazon degradation in soil typically proceeds with development of bound residue. Low sorption of bentazon suggests that this residue consists of degradation products; however, there is little data on the sorption behavior of these products. This study was undertaken to determine the sorption of bentazon and the degradation products 2-amino-N-isopropyl benzamide, 2-aminobenzoic acid, and N-methyl bentazon in Dundee silt loam and Sharkey clay, two common agricultural soils of the Mississippi Delta. Greater sorption of bentazon and degradation products in the Sharkey soil was related to finer texture and higher organic C content. Isotherms were nonlinear, with sorption increasing in the order bentazon ≪ 2-amino-N-isopropyl benzamide < N- methyl bentazon. In general, methanol extraction indicated reversible sorption of these compounds. Therefore, it is unlikely that sorption of either 2-amino-N-isopropyl benzamide or N-methyl bentazon contributes to bound residue. In contrast, essentially all of the 14C sorbed from radiolabeled 2-aminobenzoic acid solution remained bound after methanol extraction. However, due to degradation of 2-aminobenzoic acid, it was not possible to conclude the extent to which this compound contributed to bound 14C. Sorption of 14C from 2-aminobenzoic acid exceeded that of N-methyl bentazon, and at low initial concentrations (≤ 20 μM) was nearly 1000-fold greater than bentazon sorption.

Fall panicum (Panicum dichotomiflorum Michx.) seed were found to be dormant at harvest. This dormancy was overcome by an after-ripening period of 17 to 22 weeks, alternating germination temperatures (10 C for 16 h and 30 C for 8 h), stratification, and mechanical or chemical scarification. Soaking seed in gibberellic acid (GA3) or thiourea for 1 day, or washing seed in running tap water for up to 96 h before seed were placed in a germinator, had no effect on dormancy. In the greenhouse, fall panicum emergence was greatest (82%) when seed were placed on the growth media surface. The maximum number of seedlings (39%) emerged in the field when seed were placed 1.3 cm below the soil surface, although some emerged from as deep as 5.1 cm.

Foliar spray retention, absorption and translocation, and the dissipation of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] and 2,4-D [(2,4-dichlorophenoxy)acetic acid] were examined to determine their importance as selectivity factors in the response of two 2,4-DB-tolerant legumes, alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.), and two susceptible broadleaf weeds, redroot pigweed (Amaranthus retroflexus L.) and common cocklebur (Xanthium pensylvanicum Wallr.). The legumes were as effective as the broadleaf weeds in metabolizing (beta-oxidizing) 2,4-DB to 2,4-D. The relatively greater tolerance of the legumes than of the broadleaf weeds to 2,4-DB arose from a combination of poorer spray retention, less effective absorption and translocation, and a more rapid degradation of the 2,4-D arising from the beta-oxidation of 2,4-DB.

In a 3-year field study, from 51 to 1% of seed of velvetleaf (Abutilon theophrasti Medic) planted at 1 and 6-inch depths, respectively, produced established plants. Utilizing a microplot technique, 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and the ammonium salt of 3-amino-2,5-dichlorobenzoic acid (amiben) were applied at 2 and 3 lb/A, respectively, at soil depths of 0, 2, and 4 inches. Velvetleaf seed were planted at depths of 1, 2, and 3 inches. Compared with the number of plants establishing in untreated plots, surface-applied amiben reduced the number of established plants 39, 23, and 29% from seed planted at depths of 1, 2, and 3 inches, respectively. Amiben at or below seed depth gave over 95% control, and when applied below the soil surface but above the seed, 86% control. Atrazine, surface-applied, reduced weed establishment 33, 62, and 85% from seed planted at depths of 1, 2, and 3 inches, respectively. When atrazine was at, below, or above the seed but below the soil surface, control was 96% or higher.

The influence of relative planting date on the growth of common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANST), common ragweed (Ambrosia artemesiifolia L. ♯ AMBEL), sicklepod (Cassia obtusifolia L. ♯ CASOB), and redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) grown in competition with soybean [Glycine max (L.) Merr. ‘Bragg’] was studied in the greenhouse. Increases in dry matter and height were slower for the five weed species than for soybean throughout the period of the study. The root: shoot ratio of soybean was the highest of any plant in the study, while common ragweed, common cocklebur, common lambsquarters, and sicklepod were intermediate, and redroot pigweed was the lowest. Soybean dry weight was always reduced when grown in competition with a weed. Soybean dry-matter production was reduced most when weeds were planted 2 weeks before soybean, especially with common cocklebur and common lambsquarters. Weed dry-matter content was severely reduced when the weed seed were planted simultaneously with or following soybean. Soybean height was usually reduced by competition with the weeds. The height of common ragweed was increased, however, when planted simultaneously with soybean. Common lambsquarters, redroot pigweed, and common ragweed heights were increased when planted 2 weeks prior to soybean.

An assessment was made of various parameters to measure growth of soybean [Glycine max (L.) Merr. ‘Wilkin’] and einkorn (Triticum monococcum L.) cell suspension cultures to establish convenient methods of screening the effects of chemicals. Methods assessed were settled cell volumes, packed cell volumes, absorbance at 525 nm of sonicated aliquots, dry weights (of aliquots or entire flask contents), and electrical conductivity and pH of the culture medium. Settled cell volumes, conductivity, and dry-weight changes were the most useful of the methods tested for determining the phytotoxicity of a nonionic linear alcohol ethylene oxide detergent (an adduct of 1-dodecanol containing eight ethylene oxide units) and the methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Because 3 to 4 weeks were required to assess whether the cultures could grow out of the initial inhibition by the detergent or herbicide, none of the methods was rapid. Advantages and disadvantages of the various methods and their relative values for screening compounds are described.

Inheritance of glyphosate resistance was investigated in hairy fleabane populations from California as part of providing the information needed to predict and manage resistance and to gain insight into resistance mechanism (or mechanisms) present in the populations. Three glyphosate-resistant individuals grown from seed collected from distinct sites near Fresno, CA, were crossed to individuals from the same susceptible population to create reciprocal F1 populations. A single individual from each of the F1 populations was used to create a backcross population with a susceptible maternal parent, and an F2 population. Based on dose response analyses, reciprocal F1 populations were not statistically different from each other, more similar to the resistant parent, and statistically different from the susceptible parent, consistent with nuclear control of the trait and dominance to incomplete dominance of resistance over susceptibility in all three crosses. Glyphosate resistance in two of the three crosses segregated in the backcross and the F2 populations as a single-locus trait. In the remaining cross, the resistant parent had approximately half the resistance level as the other two resistant parents, and the segregation of glyphosate resistance in backcross and F2 populations conformed to a two-locus model with resistance alleles acting additively and at least two copies of the allele required for expression of resistance. This two-locus model of the segregation of glyphosate resistance has not been reported previously. Variation in the pattern of inheritance and the level of resistance indicate that multiple resistance mechanisms may be present in hairy fleabane populations in California.

Triethylamine salts of 4-amino-3,5,6-trichloropicolinic acid (picloram) plus (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) (1:1) sprays were more effective for the control of huisache (Acacia farnesiana (L.) Willd.) than for the control of Macartney rose (Rosa bracteata Wendl.) at 13 dates of application in 1969 and 1970. Both species were more controlled effectively with the application rate of 1.12 than 0.56 kg/ha. Most effective control of huisache was obtained June 18, 1970, although other summer treatments in 1970 were effective. The herbicide was, on the average, more effective on huisache and Macartney rose when applied in the evening than morning or midday. Macartney rose was most effectively controlled by treatments applied in September and October of both years. Poorest control of the two species occurred when internal water stress was highest.

Granular 4-amino-3,5,6-trichloropicolinic acid (picloram) was effective in controlling live oak (Quercus virginiana (Mill.), huisache) (Acacia farnesiana (L.), Willd.), and yaupon (Ilex vomitoria Ait.), but not honey mesquite (Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell) in south Texas. Granular 5-bromo-3-sec-butyl-6-methyluracil (bromacil) controlled live oak and huisache. Herbicides applied to soil were usually most effective in spring and fall during periods of active brush growth. Picloram granules applied in May to a mixed stand of woody plants in Puerto Rico usually were effective. However, rates up to 30 lb/A were ineffective on some species.

Three chlorsulfuron-resistant kochia accessions were tested for levels of resistance to sulfonylurea and imidazolinone herbicides, based on whole plant response and sensitivity of the target enzyme. The resistant Minot and Chester accessions were not affected by treatment with 175 g ha−1 chlorsulfuron, and I50 values for the Chester accession ranged from 22-fold (metsulfuron-methyl) to 196-fold (chlorsulfuron) higher than the susceptible Bozeman accession. However, the Chester accession was 1.5- to 2-fold more resistant than Minot to five sulfonylurea herbicides, as determined by acetolactate synthase (ALS) I50 values. The third resistant accession (Power) displayed an intermediate response and was only 2- to 5-fold more resistant than the susceptible Bozeman accession to all sulfonylurea herbicides tested. The Minot and Chester accessions were slightly cross-resistant to four imidazolinone herbicides, ranging from 2-fold (imazamethabenz, imazethapyr, and imazaquin) to 6-fold (imazapyr) more resistant than the Bozeman accession, but cross-resistance levels did not differ appreciably between the Minot and Chester accessions. The Power accession was not cross-resistant to the four imidazolinone herbicides tested. The results demonstrate that degrees of ALS resistance and cross-resistance are highly variable among kochia populations: these differences may be due to the type of mutation in the gene encoding ALS.

The effects of hogpotato interference on cotton and of the crop on the weed were measured under field conditions in four environments. Full-season interference from 105 ± 21 hogpotato plants/m2 reduced cotton plant height by 14 to 44%. Conversely, weed dry weight was reduced 54% through full-season interference from cotton. Lint yield reductions in cotton ranged from 31 to 98% following full-season weed interference. Interference during the first 7 weeks of crop growth reduced lint yield by approximately 40%; however, interference after 7 weeks of weed-free maintenance did not affect lint yield. Interference reduced boll size in 3 of 4 yr, lint percent in 2 of 4, and boll number in the only year it was measured. Cotton fiber length, uniformity index, and micronaire were reduced by full-season interference in 1 of 2 yr; however, fiber strength was not affected in either year. Significant use of soil water by hogpotato occurred at 120 cm and deeper in the soil while cotton used water primarily in the upper 75 cm.

Research was conducted from 1994 through 1996 to evaluate barnyardgrass control, rice yield, and estimated economic return with postemergence applications of propanil or propanil plus molinate applied alone or with quinclorac. Herbicides were applied at rates of 3.4, 2.8 + 2.8, and 0.17 to 0.40 kg ai ha−1 for propanil, propanil plus molinate, and quinclorac, respectively. In most trials, combinations of propanil or propanil plus molinate applied with quinclorac provided greater barnyardgrass control, rice yields, and estimated economic returns than herbicides applied alone. Propanil or propanil plus molinate applied with quinclorac at 0.28 kg ha−1 was as effective as propanil or propanil plus molinate applied with quinclorac at 0.40 kg ha−1. Applying quinclorac at 0.17 kg ha−1 with propanil plus molinate was as effective as applying quinclorac at 0.28 or 0.40 kg ha−1 with these herbicides.

Experiments with similar experimental design, soil, and planting date were conducted between 1975 and 1979 to evaluate the interference of jimsonweed on soybeans and cotton in Alabama (AL), Arkansas (AR), and Mississippi (MS). Jimsonweed densities were 0, 4, 8, 16, 32, and 64 plants 12 m−1 of row. Because of variation in rainfall patterns, geographic region influenced jimsonweed interference in cotton but not in soybeans. Even though jimsonweed interference was reduced by lack of rainfall, jimsonweed was more competitive in the less competitive cotton than in soybeans. Jimsonweed at 64 plants 12 m−1 of row was more competitive with cotton than soybeans, causing a 56 and 16% yield reduction, respectively. Position of jimsonweed to the soybean row did not influence competitiveness. Interspecific interference with soybeans caused one-third more reduction in jimsonweed fresh weight and capsules per plant than interspecific interference with cotton. The potential for jimsonweed to become a problem in southern soybeans is less than its potential in cotton because of the competitive ability of soybeans to reduce the growth and reproductive potential of jimsonweed.

Differences in the phytotoxicity of tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimehtylurea) to nine plant species were observed on the basis of calculated GR50 values. Japanese brome (Bromus japonicus Thunb.) with a GR50 value of 0.016 ppmw was the most susceptible and corn (Zea mays L. ‘Gold Rush’) with a GR50 value of 0.436 ppmw the least susceptible. There was some growth suppression with foliar application but primary activity on all species was attributed to root uptake. The most significant translocation of labeled tebuthiuron was to the tops of common ragweed (Ambrosia artemisiifolia L.) plants treated through the nutrient solution where 24.5% of the total amount recovered was detected after 24 h. Only 7.3% of the total amount recovered was detected in the top of rye (Secale cereale L. ‘Elbon’) plants with the same treatment. With both species, more than 90% of the radioactivity recovered following foliar treatments was still in the treated leaf after 24 h. Less than 5.5% of the recovered activity for both species was in the tops, less than 3% in the roots, and less than 1.5% was in the nutrient solution.

Development of genetically modified (GM) wheat has raised concerns about the movement and persistence of transgenes in agroecosystems and the ability of growers to segregate GM from conventional wheat. Wheat as a crop has been studied extensively but the population biology of volunteer wheat is not well characterized. Artificial seed bank studies were conducted in western Canada to provide baseline data on volunteer wheat seed persistence. Seed from two cultivars of Canadian western red spring wheat, ‘AC Splendor’ and ‘AC Superb’, were buried in mesh bags at three depths (0, 2, and 15 cm) in two different environments in the fall of 2003 and 2004. In addition, in 2004, ‘AC Superb’ seed were separated into small and large seed lots and buried with a medium seed lot to examine the influence of seed size on seed bank persistence. Seeds were withdrawn at intervals to assess seed germination and viability and regression analysis conducted on the viable seed at each sample period, after burial. Seed viability was variable within years and sites, and declined exponentially over time. In the spring, approximately 6 mo after initiation, viable seed ranged from 1 to 43%. With the exception of a single site and year, seeds on the soil surface persisted significantly longer than buried seeds and increasing burial depth accelerated loss of viability. The maximum viability of wheat seeds at 0, 2, and 15 cm depth in the spring following planting was 43, 7, and 2%, respectively. The extinction of viability for 99% (EX99) of the seed was estimated from regression analysis. The EX99 values of seeds buried at 0, 2, and 15 cm ranged from 493 to 1,114, 319 to 654, and 175 to 352 d after planting (DAP), respectively, with the exception of one site in 2003 where burial depths were not different and all had an EX99 value of 456 DAP. Seed size and cultivar did not significantly affect persistence, with the exception of one site in 2003 where the difference in EX99 values was 20 DAP. The rapid loss of seed viability limits temporal gene flow via volunteers in years following a wheat crop. Results provide data on spring wheat biology to aid in Canadian environmental biosafety assessments of GM wheat and will be incorporated into a mechanistic model to predict wheat gene flow on the Canadian prairies.