Growth and the chlorophyll and carotenoid contents were measured in greenhouse-grown yellow nutsedge (Cyperus esculentus L. ♯ CYPES), following treatment with glyphosate [N-(phosphonomethyl)glycine]. Herbicide was applied as a foliar spray at concentrations of 0.1, 1.0, 5.0, and 10.0 mM. After 2 weeks, growth was inhibited, and chlorosis and leaf apex necrosis were observed. Plant height was reduced, leaf fresh weight was decreased by 40%, and leaf dry weight was slightly affected. Rhizome, tuber, and secondary shoot formation was strongly inhibited, but root development was not affected by glyphosate treatment. With the 10-mM treatment, dry weight of the underground system was reduced by 80%. Chlorophyll and carotenoid levels were decreased by 52 and 54%, respectively, following glyphosate treatment.

Products were collected from rhizospheres of a hydroponically grown sorghum-sudangrass hybrid [Sorghum bicolor (L.) Moench. × Sorghum sudanense (P.) Stapf. ‘DeKalb SX17+’] (SSH) and tested for effects on seedling root growth of selected species. Phytotoxic activity was recovered in CH2Cl2 extracts of aqueous solutions of the rhizosphere products. Significant inhibition of annual ryegrass (Lolium multiflorum L.) and alfalfa (Medicago sativa L. was produced by ca. 200 ppmw (H2O weight basis) of the most phytotoxic fraction in filter-paper-disk bioassays. In soils, 70 ppmw (soil weight basis) inhibited alfalfa but not ryegrass. Among several bioassay species, alfalfa was the most sensitive and curly dock (Rumex crispus L. ♯ RUMCR) the least. Treatment of SSH plants with herbicides increased the phytotoxicity but not the amounts of materials collected. Sethoxydim {2-[1-(ethoxyimino)-butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} was detected in rhizosphere products from plants treated with the herbicide. Amounts of products collected from rhizospheres of common rye (Secale cereale L. ‘Wheeler’), johnsongrass [Sorghum halepense (L.) Pers. ♯ SORHA], and cucumber (Cucumis sativus L. ‘PI 169391’) were similar to those from SSH, but their phytotoxicities differed. Johnsongrass products were most phytotoxic, those from common rye and SSH were similar in phytotoxicity, and those from cucumber were least phytotoxic.

The translocation and root exudation of leaf-applied sublethal concentrations of 14C-labeled clopyralid (3,6-dichloropicolinic acid) and 14C-labeled 2,4-D [(2,4-dichlorophenoxy)acetic acid] were compared in Canada thistle [Cirsium arvense (L.) Scop. var. horridum Wimm. and Grab. ♯ CIRAR] at the rosette stage over a period of 9 days. The rate of absorption and export of 14C out of the treated leaf was similar for both herbicides. However, the distribution of the herbicides throughout the plant was very different. After 9 days, 15 vs. 3% of the applied 14C from 14C-clopyralid vs. 14C-2,4-D, respectively, was isolated from the foliage of the treated leaf. In the roots, twice as much 14C was recovered from the 14C-clopyralid treatments as from the 14C-2,4-D treatment at all sampling times, with 33 vs. 15% being recovered, respectively, after 9 days. When the plants were grown hydroponically, 20% of the 14C-clopyralid vs. 48% of the 14C-2,4-D was recovered in the nutrient solution during a 9-day period. No metabolites of either herbicide were recovered from the foliage, root system, or nutrient solution. Large differences in translocation of these herbicides may account for the unequal toxicity to young Canada thistle plants.

Greenhouse and laboratory investigations using four soils were conducted to determine the influence of seven herbicides on symbiotic nitrogen (N2) fixation by soybeans [Glycine max (L.) Merr. ‘Davis’]. Soils were treated with recommended rates of herbicides immediately after planting. After 8 to 10 weeks the nodulated root systems were assayed for nitrogenase activity using the acetylene (C2H2) to ethylene (C2H4) reduction technique, and total numbers and dry weights of nodules were determined. Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] (0.3 kg/ha) decreased nodule dry weight and C2H4 production per plant per hour in a Convent sandy loam. Alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl) acetanilide] (2.2 kg/ha) and prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] (0.6 kg/ha) also decreased C2H4 production per plant per hour in a Convent sandy loam, while metribuzin (0.6 kg/ha) increased C2H4 production per plant per hour and per milligram of nodule dry weight in a Mhoon silt loam. Prometryn (1.7 kg/ha) increased production of C2H4 per plant per hour in a Moreland silt loam. None of the herbicides affected C2H4 production, nodule number, or nodule dry weight in a Commerce silt loam.

The herbicide dichlobenil (2,6-dichlorobenzonitrile) inhibited soil nitrification significantly at 100 ppm following 1 and 2 weeks incubation but did not inhibit nitrification at the rates recommended for weed control.

Electrophoretic analysis of storage protein accumulation in developing cowpea [Vigna unguiculata (L.) Walp. ‘Mississippi Purple’] seed indicated that a large increase in protein content per seed occurred between 10 and 11 days after flowering (DAF). Polypeptides with molecular weights of 54, 49, and 41 kilodaltons (kD) accumulated first, and one with a molecular weight of 59 kD appeared 2 days later at 13 DAF. Treatment of plants with glyphosate [N-(phosphonomethyl)glycine] when pods were 7 and 10 DAF prevented accumulation of the major storage protein polypeptides. The accumulation of these polypeptides was not inhibited as much when pods were 11, 12, or 13 DAF at the time of treatment with glyphosate. Pod length and seed fresh weight were inhibited by glyphosate treatment of plants bearing pods 7, 10, 11, and 12 DAF. Pod width, seed dry weight, and seed length were inhibited by glyphosate when plants bearing pods 7, 10, and 11 DAF were treated.

Absorption of 14C-chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonanide} by Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] was 39% following foliar treatment and 16% when added to a nutrient solution in which the plants were growing. Translocation from the treated organ was limited regardless of treatment method; 10% of the applied 14C moved out of the treated leaf and 10% moved from the roots to other parts of the plant following absorption from the nutrient solution. When applied as a foliar treatment, 14C-chlorsulfuron had not been metabolized by Canada thistle 48 h later. However, when 14C-chlorsulfuron was added to the nutrient solution and absorbed by the roots, nearly 25% of the 14C in the plants was present as a polar product(s), 13% had an Rf value identical to benzenesulfonamide standards, and the remaining 62% was chlorsulfuron. Chlorsulfuron was not transformed similarly in a nutrient solution after 6 days in the absence of plants. Suppression of regrowth was the primary injury symptom observed following chlorsulfuron application. Chlorsulfuron also reduced whole plant weight and root bud number and weight.

Tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane] is a potent synergist of atrazine for postemergence control of weeds such as giant foxtail (Setaria faberi Herrm. ♯ SETFA) and large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA]. We determined whether: a) tridiphane could syngergize the activity of other herbicides known to be detoxified via enzymatic conjugation to glutathione, and b) differential toxicities of the synergized herbicides could provide control of proso millet (Panicum miliaceum L. ♯ PANMI) in corn (Zea mays L. “PAG SXIII”). Four herbicides were used in this study: EPTC (S-ethyl dipropylthiocarbamate), atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], CDAA (N-N-diallyl-2-chloroacetamide), and alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl) acetanilide]. Herbicides and herbicide-synergist combinations were applied postemergence. In corn, tridiphane synergized the activity of EPTC at 2 and 4 kg ai/ha, causing 22 to 25% growth reduction. Atrazine was ineffective and CDAA only slightly effective in combination with tridiphane in causing growth reduction. However, alachlor was markedly synergized by tridiphane at both 2 and 4 kg ai/ha, resulting in 36 to 54% growth reduction compared with plants treated with herbicides alone. Proso millet followed a similar trend to corn: EPTC and alachlor were effectively synergized by tridiphane, while atrazine and CDAA were ineffective. Importantly, however, the rates of herbicide used for proso millet control were much lower than those used for corn. Our data suggest that tridiphane used in combination with EPTC or alachlor could provide improved control of proso millet in corn.

The effects of several inorganic salts on the toxicity and translocation of nonradiolabeled and 14C-radiolabeled MSMA (monosodium salt of MAA) and the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] following foliar applications to purple nutsedge (Cyperus rotundus L. ♯ CYPRO) were evaluated. Salts of the monovalent cations NH4+, K+, and Na+ and to a lesser degree the anion PO4 generally resulted in increased toxicity of these herbicides. Salts of the divalent and trivalent cations Zn++ and Fe+++ frequently reduced the activity of glyphosate and MSMA, whereas salts of the divalent Ca++ ion caused little or no effect on activity. Salts of the anions Cl–, NO3–, CO3—-, and SO4– resulted in increased, decreased, or unchanged glyphosate toxicity as influenced by the associated cation. Translocation of the radiolabel of 14C-glyphosate and 14C-MSMA was increased by the addition of NH4Cl, while retention of the radiolabel within the tissue of the treated area was increased by the addition of FeCl3 to the treated leaf surface.

The influence of sublethal levels of a number of herbicides and plant growth regulators on the germinability of the seeds and the growth and development of seedlings of mouseearcress [Arabidopsis thaliana (L.) Heynh. ♯ ARBTH] was determined. Only 7 of the 22 chemicals tested had a persistent effect on progeny. Amitrole (3-amino-s-triazole) was one of the most effective compounds. It caused a characteristic bleaching only in shoot tips and pods in parent plants and appeared to act directly on the progeny by accumulation in the seed. Two auxin transport inhibitors, TIBA (2,3,5-triiodobenzoic acid) and CPII (5-O-carboxyphenyl-3-phenylisoxazole), and four of the six photosynthetic electron transport inhibitors included in the study also affected progeny. They appeared to act indirectly by interfering with seed development.

Distribution of 14C-glyphosate [N-(phosphonomethyl)glycine] in chemically treated and physically manipulated common milkweed [Asclepias syriaca (L.) ♯ ASCSY] was studied in greenhouse and growth chamber experiments. Pretreatment with glyphosate at 0.6 and 1.1 kg ae/ha 3 days prior to 14C-glyphosate application to leaves reduced the concentration of 14C recovered from shoots and leaves above the 14C-glyphosate-treated leaves but had no influence on the concentration of 14C in proximal root buds. Partial removal of the shoot and root prior to the application of 14C-glyphosate increased bud respiration and the concentration of 14C in the proximal root buds. Proximal root buds treated with 1 mM of 6-benzyl-aminopurine (BAP) for 6 days (3 days prior to application of 14C-glyphosate) contained seven times more 14C/mg than root buds of BAP-untreated plants, suggesting that dormant buds could be chemically stimulated to accumulate higher concentrations of glyphosate. BAP-treated buds were killed by foliar applications of glyphosate at 1.1 kg/ha, indicating that proximal root buds can be stimulated to acquire lethal concentrations of glyphosate.

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.

Adventitious root bud development and assimilate translocation were studied in Canada thistle [Cirsium arvense (L.) Scop. ♯ CIRAR] grown in nutrient solution in controlled environments using combinations of two photoperiods (PP) (13 and 15 h), three day/night shoot temperatures (ST) (15/5, 25/15, and 30/22 C), and three root temperatures (RT) (10, 20, and 30 C). Total root bud elongation increased with RT and length of PP and was greatest (65 cm/plant) at 25/15 C ST, 15-h PP, and 30 C RT. The number of root buds produced was greatest at 20 C RT (7.3 to 10.3 buds/plant), whereas variations in PP and ST had little effect. Total dry-matter production was greatest (7.2 g/plant) at 15-h PP, 30/22 C ST, and 20 C RT. To study phloem translocation, photoassimilates were labeled in Canada thistle plants by exposing mature leaves to 14CO2. Net assimilate translocation from a source leaf following 24-h temperature acclimation was affected little by RT and ST, but was greater under the 13-h PP than under the 15-h PP. After 7 days of temperature preconditioning, net translocation of 14C-assimilates increased with both RT and ST, but no effects due to PP were noted. With 24-h temperature acclimation, net assimilate accumulation in roots was enhanced by 13-h PP and low ST (15/5 C), whereas RT itself had no effect. In temperature-preconditioned plants, 10 C RT enhanced assimilate accumulation in roots, but ST and PP had no effect.

Translocation of 14CO2-labeled photoassimilates was compared to movement of 14C-glyphosate [N-(phosphonomethyl)glycine] in Canada thistle [Cirsium arvense (L.) Scop. ♯ CIRAR] under field and controlled-environment conditions. Field-grown Canada thistle plants were treated on mature upper leaves at the midflower stage in mid-June and harvested 8 days later. No differences were found in glyphosate and assimilate distribution, and movement was primarily basipetal. Of the glyphosate and photoassimilates translocated from the treated leaves, 25 and 31%, respectively, were recovered from the roots, while 59 and 58%, respectively, were found in the shoot tissue below the treated leaf. Concentration of labeled glyphosate in the roots as much as 95 cm from the treated shoot was as high as at the base of the treated shoot. Photoperiods that induce flowering (15 h) or maintain vegetative growth (13 h) did not differentially affect the distribution of photoassimilates or glyphosate in 7-week-old Canada thistle plants in the growth chamber. In growth chamber-grown plants equivalent amounts of glyphosate and assimilates were translocated out of treated leaves; however, relatively more glyphosate than photoassimilates accumulated in the roots.

The butyl ester of fluazifop {[(±)-2-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy)propanoic acid} at 0.26 μM in nutrient solution inhibited root growth of hydroponically grown goosegrass (Eleusine indica Gaertn. ♯ ELEIN), large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA], and giant foxtail (Setaria faberi Herrm. ♯ SETFA). Treating the soil and plant foliage at 0.035 or 0.07 kg ai/ha did not result in greater phytotoxicity than exposing only the foliage of each grass to the herbicide. Foliar-applied fluazifop was retained on the foliage in similar amounts by each of the species. Translocation of 14C to all plant parts was detected 6 h after foliar application of the butyl ester of 14C-fluazifop to the grasses in the pretillering or tillering stage. The majority (90%) of 14C absorbed by each of the species remained in the treated leaf. In hydroponic studies, each species exuded 14C into nutrient solution following foliar application of the 14C-labeled herbicide. The exuded material was predominantly fluazifop with small amounts of compounds more polar than the butyl ester of fluazifop. Uptake and translocation studies suggest that the greater sensitivity of goosegrass to fluazifop may be related to higher concentrations of the herbicide present in plant tissue.

Behavior of 14C-haloxyfop-methyl {methyl 2-[4-[(3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoate} was examined in intact plants of soybean [Glycine max (L.) Merr. ‘Mead’], shattercane [Sorghum bicolor (L.) Moench. ♯ SORVU], and yellow foxtail [Setaria glauca (L.) Beauv. ♯ SETLU] and in cell cultures of soybean and yellow foxtail. Foliar absorption of 14C-haloxyfo-methyl by intact plants was almost complete within 48 h. Significant translocation occurred within 48 h of treatment, with soybean and shattercane plants translocating more 14C than yellow foxtail. Metabolism of 14C-haloxyfop-methyl in intact plants was similar among species. Haloxyfop-methyl was rapidly hydrolyzed to haloxyfop in treated leaves and then translocated to metabolically active areas within the plants. Significant quantities of polar products were also isolated. Soybean cells in suspension culture contained higher levels of 14C than did yellow foxtail cells. Most of the 14C in soybean cells was haloxyfop-methyl, while yellow foxtail contained mostly haloxyfop.