Anionic and cationic surfactants differentially enhanced the phytotoxicities of four herbicides to corn and soybeans in relation to variations in their structure. Thirteen ionic and two related nonionic surfactants were studied in sprays containing water-soluble forms of 2,2-dichloropropionic acid [dalapon], 2,4-dichlorophenoxyacetic acid [2,4-D], 4,6-dinitro-o-sec-butylphenol [DNBP], and 3-amino-1,2,4-triazole [amitrole]. Effects of surfactant structure, type, and concentration on two other spray properties—surface tension and specific conductivity—were measured at three pH conditions.

Appreciable enhancement of herbicide toxicities occurred only at the highest concentration, 1.0 g per 100 ml (1.0 percent). With straight-chain isomers of an alkylbenzenesulfonate (ABS) anionic surfactant, enhancement of all herbicides increased as the position of the benzene ring was moved to the mid-chain (C5 and C6) carbons of an n-dodecyl alkyl group. DNBP toxicity to both species and surfactant toxicities to soybeans were increased progressively in separate odd- and even-carbon series, i.e. a C1,3,5-series and a C2,4,6-series. Other ABS variations which provided marked enhancement were use of a highly-branched dodecyl alkyl and substitution of an ester oxygen atom for the benzene ring. Among ethoxylated alkylamine cationic surfactants, variations in alkyl structure affected differentially the toxicities of the various herbicides at alkaline, neutral, and acid pH. Surfactants caused marked modification of physical-chemical properties of sprays in relation to their structure and concentration. However, no one of the properties studied could be correlated consistently with the herbicidal effectiveness of a spray. Results suggested that spray performance of herbicide formulations can be improved by using more effective surfactants to achieve other desired formulation characteristics. The increased toxicity of 2,4-D in certain alkaline sprays also suggested that the conditions necessary for absorption of 2,4-D should be examined more critically.

The compound, 3–amino–1,2,4–triazole (amitrole), has been used as an herbicide against different weed species with varying degrees of success. In the field, Canada thistle (Cirsium arvense (L.) Scop.) has been found relatively susceptible while field bindweed (Convolvulus arvensis L.) has been found relatively resistant to the action of amitrole. The reason(s) for this difference in sensitivity is not known. Because penetration of amitrole from the surface of the leaf to the interior is the first step in the chain of events leading to a response from a chemical by the treated plant, the nature of this process was examined.

The objectives were to compare the growth of black and eastern black nightshade and develop predictive models for their growth. Black and eastern black nightshade were planted on June 3 and 23, and July 12 in 1988 and May 28, June 17, and July 10 in 1989. Exponential models were strongly correlated with the growth of both species across all planting dates. Eastern black nightshade produced more biomass than black nightshade, although weight of berries was equivalent. Leaf area per plant 60 d after planting was five times greater for eastern black nightshade than black nightshade. Eastern black nightshade responded to self-shading by increasing specific leaf area.

Prohexadione calcium is an experimental turfgrass growth regulator that selectively controls or suppresses annual bluegrass in desirable turfgrass such as creeping bentgrass, Kentucky bluegrass, and perennial ryegrass. To help explain interspecific differences in turfgrass and weed response to prohexadione calcium, two laboratory trials were conducted to measure 14C-prohexadione calcium absorption, translocation, and metabolism in these four species. Annual and Kentucky bluegrass absorbed more prohexadione calcium than creeping bentgrass and perennial ryegrass when averaged over harvest timing and trial. Radioactivity partitioning to other foliage did not differ between species but annual bluegrass and Kentucky bluegrass translocated more radioactivity to roots and evolved more radioactive CO2 than creeping bentgrass and perennial ryegrass. Thin-layer chromatographic separations indicate radioactivity was translocated predominately as prohexadione calcium. When averaged over species and trial, 25 and 16% of recovered prohexadione calcium was metabolized within 1 h after treatment in treated leaves and other foliage, respectively. The rate of metabolic degradation was 0.7% h−1 in treated leaves and 0.4% h−1 in other foliage. Previous research indicates that annual and Kentucky bluegrass growth is suppressed more by prohexadione calcium than is growth of creeping bentgrass and perennial ryegrass. Increased prohexadione calcium absorption partially explained these interspecific differences in growth suppression.

Drunken horse grass [Achnatherum inebrians (Hance) Keng] is a perennial poisonous weed in western China. A comprehensive understanding of the ecological response of A. inebrians germination to environmental factors would facilitate the formulation of better management strategies for this weed. Experiments were conducted under laboratory conditions to assess the effects of various abiotic factors, including temperature, light, water, pH, and burial depth, on the germination and seedling emergence of A. inebrians. The seeds germinated at constant temperatures of 15, 20, 25, 30, and 35 C and in alternating-temperature regimes of 15/5, 20/10, 25/15, 30/20, 35/25, and 40/30 C, and the germination percentages under constant and alternating temperatures ranged from 51% to 94% and 15% to 93%, respectively. Maximum germination occurred at a constant temperature of 25 C, and germination was prevented at 45/35 C. Light did not appear to affect germination. The germination percentage of seeds was more than 75% in the pH range of 5 to 10, with the highest germination percentage at pH 6. The seeds germinated at osmotic potentials of 0 MPa to −1.0 MPa, but decreasing osmotic potential inhibited germination, with no germination at −1.2MPa. After 21 d of low osmotic stress, the seeds that did not germinate after rehydration had not lost their vitality. The seedling emergence percentage was highest (90%) when seeds were buried at 1 cm, but declined with increasing burial depth, with no emergence at 9 cm. Deep tillage may be effective in limiting the germination and emergence of this species. The results of this study provide useful information on the conditions necessary for A. inebrians germination and provide a theoretical basis for science-based prediction, prevention, and control of this species.

Weed invasion is a prevailing problem in modestly managed lawns. Less attention has been given to the exploration of the role of arbuscular mycorrhizal fungi (AMF) under different invasion pressures from lawn weeds. We conducted a four-season investigation into a Zoysia tenuifolia Willd. ex Thiele (native turfgrass)–threeflower beggarweed [Desmodium triflorum (L.) DC.] (invasive weed) co-occurring lawn. The root mycorrhizal colonizations of the two plants, the soil AM fungal communities and the spore densities under five different coverage levels of D. triflorum were investigated. Desmodium triflorum showed significantly higher root hyphal and vesicular colonizations than those of Z. tenuifolia, while the root colonizations of both species varied significantly among seasons. The increased coverage of D. triflorum resulted in the following effects: (1) the spore density initially correlated with mycorrhizal colonizations of Z. tenuifolia but gradually correlated with those of D. triflorum. (2) Correlations among soil properties, spore densities, and mycorrhizal colonizations were more pronounced in the higher coverage levels. (3) Soil AMF community compositions and relative abundances of AMF operational taxonomic units changed markedly in response to the increased invasion pressure. The results provide strong evidence that D. triflorum possessed a more intense AMF infection than Z. tenuifolia, thus giving rise to the altered host contributions to sporulation, soil AMF communities, relations of soil properties, spore densities, and root colonizations of the two plants, all of which are pivotal for the successful invasion of D. triflorum in lawns.

Multiple applications of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] during the winter, spring, and summer were evaluated for bahiagrass (Paspalum notatum F.) control in centipedegrass [Eremochloa ophiuroides (Munro) Hack.]. Single and repeated atrazine, metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)-one], and methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] treatments were applied in the spring for common lespedeza [Lespedeza striata (Thunb.) H. & A. ‘Kobe’] control in centipedegrass. Atrazine at 2.2 kg/ha in two (July + August) or three (January + April + May, April + May + July, or May + July + August) applications controlled bahiagrass without injuring centipedegrass turf. In most instances repeated treatments were needed a second year for consistent control of 98 to 100%. A single treatment of atrazine at 2.2 kg/ha, metribuzin at 0.6 kg/ha, or methazole at 1.1 kg/ha satisfactorily controlled emerged common lespedeza in centipedegrass turf. None of the treatments injured centipedegrass. When atrazine was applied to actively growing centipedegrass, the turf had a darker green color than untreated turf. This usually occurred within a month after treatment and lasted for 3 to 4 weeks.

Five rigid ryegrass populations suspected of being resistant to both glyphosate and oxyfluorfen were collected in southern Spain and tested under laboratory-controlled conditions. Four populations (Depuradora, Condado, AlamoRasilla, and Portichuelo) were treated with glyphosate for at least 15 consecutive years, and treatments during the last 5 yr were mixed with oxyfluorfen. The fifth population (4alamos) followed the same glyphosate treatment, although oxyfluorfen was never used to control it. Dose–response assays confirmed glyphosate resistance in all populations, with resistance indexes ranging from 11.7 to 37.5 (GR90). Shikimate accumulation assays consistently supported these data, as the most glyphosate-resistant populations (Depuradora and Condado) displayed the lowest shikimate levels. Surprisingly, four populations (Depuradora, Condado, AlamoRasilla, and Portichuelo) displayed 7.93- to 70.18-fold more resistance (GR90) to oxyfluorfen, despite limited selection pressure, showing a similar resistance pattern as that for glyphosate. The 4alamos population displayed oxyfluorfen GR90 values that were similar to those observed in susceptible plants; however, this population was significantly more resistant in terms of plant survival (LD90). Protoporphyrin IX accumulation assays supported the results of dose–response assays, in that the most oxyfluorfen-resistant populations accumulated less protoporphyrin IX. Although more studies are needed, it seems that these five glyphosate-resistant weed populations display a natural tendency to easily develop resistance to oxyfluorfen, with the populations that have higher resistance to glyphosate also having higher resistance to oxyfluorfen.

Histological abnormalities were found in Canada thistle (Cirsium arvense (L.) Scop.) roots after plants received foliar treatments of 4-amino-3,5,6-trichloropicolinic acid (picloram). These abnormalities included destruction and distortion of cortical cells and cambial and phloem disintegration. Some or all of these conditions were present, depending upon which portion of the root was sectioned.

Amitrole (3-amino-1,2,4-triazole) was applied to purple nutsedge (Cyperus rotundus L.) clones newly established in the field in the Piedmont Plateau. Applications were made one week after initial foliar emergence, then at biweekly intervals through the 20th week. The principal results were: (1) Nutsedge was most susceptible to amitrole applied 4 weeks after initial emergence. The next most susceptible stages were at 1 or 2 weeks; (2) Six weeks after emergence, nutsedge appeared resistant to amitrole; (3) All applications after 10 weeks were relatively ineffective; (4) Chemical analyses of tubers and bulbs indicated a high ash content early in the season, particularly at 6 weeks after emergence.

In an attempt to improve the metering of herbicides applied to soil in horticultural plantings, loosely knitted cellulose acetate cloth was impregnated with herbicides, using appropriate acre rates as determined by those used in spray applications. Treated cloth was placed on the soil and the edges anchored or the cloth was lightly covered with soil. Adjacent plots were sprayed with the same herbicides. The herbicide-impregnated cloth was as effective as spray applications of 12 of the 15 herbicides used.

Response of wild oat (Avena fatua L.) at the three-leaf stage to five postemergence herbicides, asulam (methyl sulfanilylcarbamate), barban (4-chloro-2-butynyl m-chlorocarbanilate), diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, difenzoquat (1,2-dimethyl-3,5-diphenyl-1 H-pyrazolium), and flamprop [N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine] was measured and compared in nine physiological and biochemical processes (chlorophyll content, photosynthesis, photosynthate translocation, and changes in ATP, lipids, DNA, RNA, amino acids, and proteins). Content of chlorophyll a and b was reduced by the application of diclofop and difenzoquat. Photosynthesis was inhibited with all five herbicides, but photosynthate translocation from the leaves to the roots was reduced only with diclofop, difenzoquat, and flamprop. ATP production was inhibited by all herbicides except flamprop, which increased the ATP content. Incorporation of 32P into lipids was reduced by all herbicides except asulam. The incorporation of 32P into nucleic acids (DNA and RNA) was inhibited by all five herbicides. Serine and threonine, especially the latter, accumulated in large quantity with all herbicides except difenzoquat. Protein content (water-soluble,-insoluble, and total amount) was reduced by asulam, diclofop, and flamprop, but barban and difenzoquat reduced water-insoluble and total proteins only. Apparently, all herbicides examined affected more than one physiological function and biochemical process in wild oat.

The potential of several common weed species to produce adventitious shoots when the plants were excised approximately 1.0 cm below the cotyledonary node at the cotyledon growth stage and at the four true-leaf stage is reported. Indian jointvetch (Aeschynomene indica L. ♯3 AESIN), northern jointvetch [Aeschynomene virginica (L.) B.S.P. ♯ AESVI], and wild poinsettia (Euphorbia heterophylla L. ♯ EPHHL) produced adventitious shoots at both growth stages after shoot excision. Adventitious and vegetative regeneration of wild poinsettia damaged by herbicides was similar to that from decapitation.

Seedling vernalization was more effective than seed vernalization in promoting flowering of downy brome (Bromus tectorum L. # BROTE). Vernalizing imbibed downy brome caryopses at 3 C for 0 to 30 days did not induce rapid flowering when the caryopses were planted. Downy brome seedlings were exposed for 30 days to six photoperiod/temperature treatments. After subsequent transfer to long days, plants from the short-day/3 C treatment flowered within 30 days. Flowering was delayed or was absent in treatments with higher temperatures or long days. The shoot apex increased in volume during the short-day/3 C vernalization period. Two days following vernalization, floral initiation had occurred. By day 5, lateral organs had proliferated. Rudimentary glumes and lemmas were visible by day 8.

The vapor pressures of the four most common commercial low-volatile esters and a reference high-volatile ester of 2,4-dichlorophenoxyacetic acid (2,4-D) were determined by gas-liquid chromatography. The order of increasing volatility and the vapor pressure of these esters in mm of Hg at 187 C are as follows: isooctyl—2.7; 2-ethylhexyl—3.0; butoxy ethanol—3.9; propylene glycol butyl ether—3.9; and the reference, isopropyl—16.7. Extrapolations to 25 C support this ranking at working temperatures. Commercial esters of 2,4-D derived from long-chain hydrocarbon alcohols are in the same volatility range as the commercial esters containing an ether linkage.

The physiological basis for tolerance and susceptibility of four lines of cucumber (Cucumis sativus L.) to the methyl ester of 3-amino-2,5-dichlorobenzoic acid (chloramben) was investigated. ‘MSU 3207’ and ‘MSU 0612’ were tolerant (T), whereas ‘MSU 3159’ and ‘MSU 0866’ were susceptible (S). Intraspecific variability was related to higher concentrations of chloramben in the roots of the susceptible lines, resulting from metabolic differences in these lines and rapid absorption of the herbicide by the roots of ‘S-MSU 3159’. Tolerance of ‘T-MSU 3207’ resulted primarily from low uptake and reduced translocation of the herbicide, while tolerance of ‘T-MSU 0612’ was related to, but not necessarily explained by, a peculiar 14C-label distribution pattern in the leaves. Thin-layer chromatographic analysis of methanol-soluble extracts from the lines studied 3 days after 14C-chloramben methyl ester treatment separated six 14C-metabolites in the roots and five in the shoots. After a 4-hr treatment, 14C-chloramben methyl ester was absorbed and translocated more rapidly than 14C-chloramben by all four lines. Tolerance or susceptibility did not always correlate with the total concentration of radioactivity in methanol-soluble shoot and root extracts.

Benzyl isothiocyanate (BITC) was formulated in dry granules with tung oil and calcareous loess to facilitate safe handling of the water-sensitive lachrymator. Crop and weed seeds were exposed to granular BITC at 40 mg ai/kg (w/w) substrate on moist sand for 2 days. When the pretreated seeds were washed with water and placed on BITC-free sand in a germination chamber for 15 days, germination in comparison to untreated seeds was 0 to 8% for pitted morningglory (Ipomoea lacunosa L. # IPOLA), sicklepod (Cassia obtusifolia L. # CASOB), milo [Sorghum bicolor (L.) Moench. ‘Funks G-522DR’], and red rice (Oryza sativa L. # ORYSA) seeds; 15 or 16% for velvetleaf (Abutilon theophrasti Medic. # ABUTH) and johnsongrass [Sorghum halepense (L.) Pers. # SORHA]; and 39% for barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG]. Subjecting milo seeds to moist sand medium that contained BITC granules at 10, 20, and 40 mg ai/kg substrate reduced germination of milo by 78, 97, and 100%, respectively. However, BITC granules applied to the growth medium 2 to 4 days prior to sowing seeds had little effect on germination and growth of milo or sicklepod. Thus, BITC-treated soil soon became safe for newly sown seeds, but seeds present in soil when the toxin granules were applied failed to recover from exposure to BITC and deteriorated within 15 days.

Soil uptake, translocation, and metabolism of simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) by tolerant poplar clone Populus × euramericana I-45/51, a section Aigeiros hybrid, and intolerant clone P. maximowiczii × P. trichocarpa Kingston, a section Tacamahaca hybrid were compared. Concentrations of simazine in the two clones were not different 48 h and 1 week after application. However, the presence of 2-chloro-4-amino-6-ethylamino-s-triazine (G-28279), a less toxic simazine metabolite, was detected in tolerant clone I-45/51 after 12 h and it increased steadily through 1 week after simazine application. In contrast, no trace of G-28279 was found in susceptible clone, Kingston.

Net (apparent) photosynthesis rate (Pn) of jointed goatgrass (Aegilops cylindrica Host # AEGCY) leaves in the greenhouse became light saturated at a photosynthetic photon flux density (PPFD) of about 1000 μE·m–1-2·s–1 with a maximum Pn of 27 mg CO2 ·dm–2 ·h–1. Diffusive resistance to water vapor (rl) of adaxial leaf surfaces was 43% that of abaxial surfaces, in part, because stomatal density was 50% greater on adaxial leaf surfaces than on abaxial surfaces. Dark respiration rate (Rd) was 1.6 mg CO2 ·dm−2·h−1. Light compensation point (CPl) was 21 μE·m−2·s−1 and CO2 compensation point (CPc) was 32 ppmv. In the field, where light intensity and temperature were greater than in the greenhouse, leaves became light saturated for Pn at a higher intensity, and Rd and CPl were three times greater than in the greenhouse. Pn and Rd of spikes at anthesis were at least 30% less and 200% greater, respectively, than the values for leaves.

Terbacil (3 - tert - butyl - 5 - chloro - 6 - methyluracil) uptake by roots and translocation were evaluated as possible bases of tolerance in two species, strawberry (Fragaria × ananassa Duchesne 'Sunrise’ and ‘Guardian’) and goldenrod (Solidago fistulosa Miller). Tolerance of goldenrod to terbacil was at least five-fold that of strawberry. Strawberry was at least four - fold more tolerant than highly terbacil - sensitive cucumber (Cucumis sativus L. ‘Chipper’). Guardian, a reported susceptible strawberry cultivar, was as tolerant to terbacil as the tolerant cultivar, Sunrise. Distribution of 14C within the plant, but not uptake of label through roots, was found to be correlated to relative tolerance to terbacil when the roots of intact plants of all species were exposed for various time periods to a nutrient solution containing 2 -14C terbacil. The observed distribution patterns suggest that tolerance to terbacil in strawberry and goldenrod is at least partially attributable to the restricted translocation of root - absorbed herbicide. The greater tolerance of goldenrod than strawberry to terbacil was apparently unrelated to the restriction of herbicide to root tissue.