A pine kraft lignin (PC940C) controlled the release of 14C-chloramben (3-amino-2,5-dichlorobenzoic acid), 14C-metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], and 14C-alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] as measured by water leaching in soil columns. As more PC940C was used, a concentration effect was found with more of the three herbicides being retained in the top portion of the soil columns. Combinations of alachlor and metribuzin applied with PC940C did not alter the retention in the top portion of the soil columns of either 14C-metribuzin or 14C-alachlor compared to each herbicide applied with PC940C alone. This would suggest that, at the rate of PC940C used, there was no competition between either herbicide for the controlled-release function of PC940C. The percentage of 14C-chloramben, 14C-metribuzin, and 14C-alachlor retained by PC940C in the top portion of the columns was very similar. Combinations of metribuzin and alachlor without PC940C reduced the mobility of both 14C-metribuzin and 14C-alachlor. Finally, 3H-PC940C was found to be immobile in soil columns leached with water.

Leaves absorbed high amounts of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) as foliar sprays on honey mesquite (Prosopis glandulosa Torr. # PRCJG) as indicated by concentrations of 10 μg/g fresh wt or more in basal stem phloem by 4 days after treatment. Small quantities of clopyralid (< 1 μg/g) were detected in basal stem phloem after spray applications of clopyralid to defoliated plants or roots treated by soil application. When applied to foliated plants, the 0.56 kg/ha of clopyralid killed 60% or more plants, but none were killed when clopyralid sprays were applied to defoliated plants or when 2.2 kg/ha of clopyralid was applied to the soil. Water, diesel oil plus water, or water plus surfactant were equally effective as clopyralid carriers as foliar sprays.

Two parameters of physiological competence, rate of CO2 fixation and intraspecific competitiveness, were determined for one or more atrazine-resistant isolates of the photosynthetic bacterium Rhodobacter sphaeroides. Measured over a 2-h period under optimal conditions, two of the resistant isolates fixed CO2 at a greater rate than the atrazine-susceptible, wild-type organism. In a mixed culture study, an atrazine-resistant strain was able to grow and compete successfully with the susceptible, wild-type strain for at least 14 days.

The absorption and translocation patterns of foliar applied 14C- chlorsulfuron {2-chloro-N- [[(4-methoxy-6-methyl-1,3,5- triazin- 2 - yl)amino] carbonyl] benzenesulfon-amide} and 14C-metsulfuron {2- [[[[(4-methoxy-6-methyl-1,3,5- triazin- 2-yl)amino] carbonyl] amino] sulfonyl] benzoic acid} in wild garlic (Allium vineale L. # ALLVI) were similar. Both 14C-chlorsulfuron and l4C-metsulfuron were readily absorbed by wild garlic, with 62 and 58%, respectively, of the applied doses absorbed 144 h after application. After 144 h, 17% of the applied 14C-chlorsulfuron and 16% of the applied 14C-metsulfuron were translocated out of the treated leaf, with the greatest amounts concentrating in young shoot tissues. Chlorsulfuron and metsulfuron reduced wild garlic shoot dry weight, height, and the number of leaves, more when they were applied to the foliage, or to both the foliage and the soil, than when they were applied to the soil alone.

Imazaquin {2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-3-quinolinecarboxylic acid} site of uptake and toxicity from soil application were investigated in yellow nutsedge (Cyperus esculentus L. #3 CYPES) and purple nutsedge (C. rotundus L. # CYPRO). Imazaquin concentrations of 0.1 to 0.5 ppmw inhibited yellow nutsedge shoot emergence completely, while purple nutsedge shoots emerged at the lower concentrations. Herbicide placement above the tuber reduced shoot emergence and shoot and root dry weights of both species more than did placement below the tuber. Increasing herbicide rate increased the number of tuber buds that sprouted. Three-day-old nutsedge propagules absorbed 14C-imazaquin from both rhizome shoots and roots and the herbicide moved both acropetally and basipetally in nutsedge propagules.

14C-labeled 4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4H)-one (ethiozin)3 was metabolized more rapidly in tolerant than in sensitive wheat, Triticum aestivum L., cultivars. After a 6-h herbicidal pulse, the main metabolites were conjugates at all incubation times up to 48 h. The levels of deaminated and dethioethylated metabolites never exceeded 4% of the extractable radioactivity and also did not differ between tolerant and sensitive plants. On the contrary, 92% of the extractable radioactivity was in conjugates after 24 h in the leaves of tolerant plants compared to 25% in the leaves of sensitive plants. The differently sensitive wheat cultivars conjugated metribuzin, 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one, at about half the rate that was observed with ethiozin. This finding may explain the fact that most wheat cultivars are more sensitive to metribuzin compared with ethiozin.

Absorption of foliar-applied 14C-imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} 72 h after treatment was higher than 90% for soybean [Glycine max (L.) Merr. ‘Braxton’], peanut (Arachis hypogaea L. ‘Florunner’), common cocklebur (Xanthium strumarium L. # XANST), sicklepod (Cassia obtusifolia L. # CASOB), and Florida beggarweed [Desmodium tortuosum (SW.) # DEDTO]. Both symplasmic and apoplasmic translocation of the herbicide were evident. Imazaquin half-life was 4.4 days in soybean, 5.3 days in peanut, 9.6 days in Florida beggarweed, 12.7 days in sicklepod, and 39.8 days in cocklebur. Tolerance of these species to foliar-applied imazaquin as determined in greenhouse studies with 21-day-old seedlings was as follows: soybean = peanut > Florida beggarweed > sicklepod > cocklebur. Tolerance was directly correlated to imazaquin halflife within the tissue of the respective species.

Previous reports have suggested that bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] tolerance among soybean genotypes is the result of differential translocation or metabolism. The basis for tolerance was reexamined using susceptible and tolerant genotypes. Tolerant genotypes (‘Hill’ and ‘Clark 63’) were found to tolerate 100- to 300-fold more bentazon than susceptible genotypes (‘L78–3263’, ‘Hurrelbrink’, and ‘PI 229.342’). Minor differences in absorption and translocation occurred among the genotypes but they did not correlate with tolerance. Tolerant genotypes metabolized 80 to 90% of absorbed bentazon within 24 h, while susceptible genotypes metabolized only 10 to 15%. Two major metabolites, the glycosyl conjugates of 6- and 8-hydroxybentazon, were formed in tolerant genotypes. Susceptible genotypes did not form the hydroxybentazon conjugates but instead produced relatively low levels of two unidentified metabolites. It is concluded that differential bentazon tolerance among soybean genotypes is linked to the ability to form both the 6- and 8-hydroxybentazon conjugates.

The response of potato (Solanum tuberosum L. 'Superior’) to glyphosate [N-(phosphonomethyl)glycine] at rates between 0.28 and 2.24 kg ae/ha was determined in four environments: 24/13 or 13/4 C temperature regimes with light levels of 650 ± 53 or 320 ± 45 μE · m−2 · S−1. Light level did not affect phytotoxicity ratings or shoot fresh weight following glyphosate application. Greater phytotoxicity and reduced fresh weight accumulation were observed from glyphosate at rates above 0.56 kg/ha in a high-temperature regime than for comparable plants grown at low temperature. Studies of 14C-glyphosate uptake and translocation indicated that the differences in phytotoxicity were due to less glyphosate absorption at low temperature and not a shift in distribution patterns within the plant.

A growth cabinet study was conducted to evaluate the effect of temperature on the distribution of several herbicides in quackgrass. Uniformly labeled 14C-sucrose and the radiolabeled herbicides glyphosate, sethoxydim, cloproxydim, the butyl ester of fluazifop, the methyl ester of haloxyfop, and the ethyl ester of quizalofop were applied to quackgrass grown at three day / night temperature regimes (10/5, 20/15, and 30/25 C). Seven days after treatment the plants were harvested, lyophilized, and later sectioned, mapped, and oxidized in preparation for 14C quantification. Quackgrass rhizome growth was more vigorous at 20/15 than 30/25 or 10/5 C. of the herbicides tested, haloxyfop was the most inhibitory to rhizome growth. Temperature increases from 10/5 to 20/15 or from 20/15 to 30/25 C resulted in more translocation to shoots. Increasing temperature had various effects on translocation to rhizomes depending on the chemical applied. At all three temperature regimes, more 14C was recovered from distal than basal buds in plants treated with 14C-sethoxydim. In contrast, at all three temperature regimes, similar amounts of 14C were recovered from the distal and basal buds of plants treated with 14-C-sucrose.

In laboratory and field studies, quackgrass (Agropyron repens (L.) Beauv. # AGRRE) was subjected to postemergence applications of the butyl ester of fluazifop-P {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, or ethyl ester of quizalofop {2-[4-[[6-(chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid}. Haloxyfop, fluazifop-P, and quizalofop each required a minimum of 1 week to reduce quackgrass transpiration or water uptake in the laboratory. At rates lower than 0.56 kg ae/ha, fluazifop-P reduced quackgrass transpiration and water usage less quickly and to a lesser extent than equivalent rates of haloxyfop and quizalofop. The time required for significant transpiration and water uptake reduction by herbicide-treated quackgrass was several days longer in the field than in the laboratory, but the reaction patterns among the herbicides were similar. Little if any benefit was obtained from sequential applications of the herbicides compared with single applications of the same total dosage. All three herbicides significantly reduced quackgrass dry weight.

Greenhouse and laboratory experiments were conducted to study the activity of foliar-applied chlorimuron in yellow and purple nutsedge. Foliar-applied chlorimuron caused injury to both yellow and purple nutsedge at rates as low as 5 g ai/ha. Visible injury increased as rates increased from 5 to 20 g/ha at all weekly evaluation dates. At 28 days after application, there was 84% control of yellow and 100% control of purple nutsedge from 20 g/ha of chlorimuron. In both species, all rates of chlorimuron reduced shoot dry weight, inhibited secondary shoot production, and inhibited resprouting of parent tubers attached to treated plants. Over 92% of the applied label was recovered, when 15 μl of 3.46 mM 14C-chlorimuron solution containing 0.18 μCi was applied to a 1 cm2 area in the middle of the fourth fully expanded leaf. Over 12% of the total 14C applied was absorbed, with over 15% of that being translocated within 1 day after application in both species. More than 76% of the absorbed 14C in yellow nutsedge and 72% in purple nutsedge remained in the treated area. In both species, basipetal transport was limited. Analysis of plant tissue extracts by thin-layer chromatography indicated slow degradation of chlorimuron in both species. Susceptibility of yellow and purple nutsedge to chlorimuron appears to be due to the rapid absorption and translocation rates in relationship to the slow degradation rate of the active parent compound.

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

A mechanism of action of the ethyl ester of quizalofop was determined in monocotyledonous and dicotyledonous plants. Quizalofop inhibited electron transport in both cucumber and corn chloroplasts. In corn, inhibition of electron transport was more pronounced under phosphorylating conditions. Half-maximal inhibition (I50) of ATP synthesis was achieved with a 75-μM concentration of quizalofop in coupled corn chloroplasts. Cucumber chloroplast ATP synthesis was not inhibited at herbicide concentrations up to 100 μM. Corn chloroplast fractions contained greater quantities of bound [U-14C] quizalofop ester following incubation in light and dark assays. Thin-layer radiochromatograms of 14C-labeled quizalofop showed no metabolism or degradation of parent ester incubated in light and dark chloroplast-mediated reactions. In our studies, it is apparent that the inhibitory action of quizalofop was due to the parent ester. The ester formulation of quizalofop appears to exhibit multiple activity in susceptible plant chloroplasts.

Two lettuce cultivars exhibiting differential levels of tolerance to thiobencarb in soil and nutrient solution assays were examined. Seedlings of ‘Dark Green Boston’ (BOS), a susceptible cultivar, were found to show significant inhibitions in foliar growth compared to the tolerant ‘Great Lakes 366’ (GLA). Reductions of 57% occurred in BOS leaf dry weights at rates of 3 μM thiobencarb as soon as 4 days after treatment. In addition, growth abnormalities including fused leaves were observed in the BOS cultivar, indicating inhibition early in leaf development at the meristem. Twenty-nine and 22% of applied 14C-thiobencarb was absorbed from nutrient solution by BOS and GLA, respectively. This difference is probably due to BOS having a 50% greater root system at the time of treatment. Greater absorption and accumulation of radioactivity in the leaves, as well as significantly greater amounts of parent 14C-thiobencarb in the foliage of BOS compared to GLA (30 and 19%, respectively) may account for the selectivity observed. Metabolism of 14C-thiobencarb occurred within 1 day in both cultivars, with the apparent production of herbicide conjugates accounting for more than 90% of the extracted radiolabel 12 days after treatment. A thiobencarb sulfoxide metabolite was not identified in these studies, indicating sulfoxide production is not a mechanism of selectivity in lettuce.

A mathematical model describing the behavior of 14C-haloxyfop {2-[4-[(3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} and its methyl and ethoxyethyl esters on yellow foxtail [Seteria glauca (L.) Beauv. #3 SETLU] has been developed to evaluate volatility, penetration, ester transformation, metabolism, and transport of the chemical in the plant system. The effects of crop oil concentrate, temperature, structure of the molecule, and the addition of bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] to the application solution on the kinetic rate constants have been studied. Crop oil concentrate was found to dramatically increase penetration at an optimal level of approximately 0.3% (v/v). Significant increases in rate constants were observed at higher temperatures. Esters were rapidly converted to the acid in the plant with conversion of the ethoxyethyl ester being approximately twice as fast as the methyl ester. Subsequent metabolism of the acid proceeded at a moderate rate which was independent of the original ester form of the molecule. All kinetic processes were described by first-order rate constants with the exception of transport which appeared to slow a few hours after application even though acid levels in the plant were high. When bentazon was applied in combination with haloxyfop-methyl, penetration of the ester was somewhat inhibited, while transport of radioactivity associated with the molecule to other plant parts was dramatically reduced.

The effects of caffeic, vanillic, p-coumaric, chlorogenic, and ferulic acids, ragweed parthenium (Parthenium hysterophorus L. # PTNHY) residue and extracts on the growth, ion uptake, and chlorophyll content of 3-week-old tomatoes (Lycopersicon esculentum Mill. ‘Walter’) grown in the greenhouse were determined Vanillic, p-coumaric, chlorogenic, and ferulic acid at 10−3 M and parthenium extract at 0.5% (w/v) significantly reduced tomato root and shoot dry weight. Ragweed parthenium residue at 0.5% (w/w) and extract at 0.5% (w/v) significantly reduced tomato shoot and root dry weight. Leaf nitrogen content was reduced by phenolic acids (10−3 M) and ragweed parthenium extract (0.5%). Phosphorus content was reduced by all phenolic acids at 10−3 M and ragweed parthenium extract at 0.5% (w/v). In addition, p-coumaric and ferulic acids at 10−4 M reduced phosphorus content. No consistent relationship between chlorophyll content and tomato growth reduction was observed.

Experiments were conducted to determine whether differences in sensitivity of sunflower (Helianthus annuus L.), and rapeseed (Brassica napus L.) to 14C-picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) and 14C-clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) can be attributed to differences in absorption, translocation, or metabolism of the herbicides. Within 24 h, more than 97% of the radioactivity from picloram or clopyralid was absorbed by the foliage of both plant species. Acropetal transport of both herbicides was similar in the two plant species, with approximately 60% or more of the recovered radioactivity from picloram and clopyralid treatments moving acropetally out of the treated leaf 144 h after application. Less than 6% of the 14C-label from either herbicide treatment moved basipetally in both species. Therefore, differences in absorption and translocation did not account for intra- or inter-species sensitivity differences to the two herbicides. Significantly more 14C-picloram and 14C-clopyralid was converted to water-soluble metabolites in rapeseed than in sunflower plants. However, in rapeseed plants, the pattern of metabolism of both herbicides was similar, indicating that the difference between the metabolism of picloram and clopyralid did not account for the sensitivity difference within this species. It appears that only one picloram and clopyralid metabolite was formed in both plant species as determined by TLC. The metabolite of picloram or clopyralid was a water-soluble conjugate that yielded the carboxylic acid amide of the respective herbicide upon ammonolysis.

The influence of various additives on CGA-82725 [2-propanyl-2,4-(3,5-dichloro-2-pyridyloxy)phenoxy propanoate] absorption and translocation was determined in oats (Avena sativa L. ‘Lyon’). The absorption and translocation of 14C was greater when 14C-CGA-82725 was applied with petroleum oil compared to soybean [Glycine max (L.) Merr.] oil. The translocation of 14C was greater at 96 than 48 h after 14C-CGA-82725 application. The absorption of 14C was greater at 48 than 24 h but was similar at 48 and 96 h after 14C-CGA-82725 application with no additive, petroleum oil, or soybean oil. The absorbed and translocated 14C was greater when 14C-CGA-82725 was applied with oil at 1.2 compared to 0.6 L/ha. No additional increase in 14C absorption and translocation was obtained if the oil volume was increased to 2.3 L/ha. The addition of petroleum oil to 14C-CGA-82725 increased 14C absorption and translocation more than the addition of palm (Eleais quineeneis Jalq.), safflower (Carthamus tinctorius L.), linseed (Linum usitatissimum L.), or soybean oil. The four seed oils and the emulsifier At Plus 300F caused similar increases in 14C absorption and translocation over 14C-CGA-82725 applied alone. Ethylene glycol did not increase 14C absorption and translocation compared to 14C-CGA-82725 applied alone.

Metabolism and phytotoxicity of bentazon by suspension-cultured cells of soybean and velvetleaf were compared. Growth of suspension cells of both species was reduced when the cells were exposed to increasing concentrations of bentazon. However, soybean plants were tolerant and velvetleaf plants were susceptible to postemergence applications of bentazon. After incubation with 1 μM 14C-bentazon for 6 h, soybean and velvetleaf cells in the log phase of the culture growth cycle contained similar levels of 14C (6 nmol/g fresh weight). Of the total 14C in the soybean cells, 57 to 92% was present as the glucosyl conjugates of 6-OH- and 8-OH-bentazon with the remainder present as bentazon; the percentage depended on the phase of the culture growth cycle. Bentazon metabolism was greatest in the stationary phase of growth. Thin, transverse sections of soybean hypocotyl metabolized bentazon to the same two metabolites as soybean suspension cells did. The ratio of 6-O-glucosyl-bentazon to 8-O-glucosyl-bentazon was always greater than 1:1 for both the hypocotyl sections and the suspension cells. Bentazon metabolites were not detected in the velvetleaf cells, the velvetleaf hypocotyl sections, or the media of either species. Soybean suspension-cultured cells appear to be a valid and advantageous system for studying the hydroxylation and glucosylation of bentazon, the primary reactions believed to be responsible for detoxication of the herbicide in tolerant plants.