Tolerance to glufosinate has been bioengineered into cotton through the expression of a gene encoding the enzyme phosphinothricin acetyl transferase (PAT). Studies were conducted to determine thermal limitations on herbicide efficacy in bioengineered cotton. The 50% inhibition (I50) of glufosinate of the target-site enzyme glutamine synthetase was thermally dependent with the lowest values between 25 and 35 C. Larger values of I50 were measured above and below the 25 to 35 C range. The apparent Michaelis constant KM of the enzyme PAT was relatively stable from 15 to 30 C and increased more rapidly from 30 to 45 C. The two components in combination suggest the aggregate tolerance to glufosinate would not be thermally limited between 15 and 45 C. The thermal dependence of the aggregate tolerance in cotton suggests that glufosinate would not damage the crop over a range of temperatures. This prediction is in agreement with the results of field studies carried out over a number of years, which showed the glufosinate-tolerant cotton to be undamaged by glufosinate over a wide range of temperatures.

Seeds of common yarrow (Achillea millefolium L.) germinated 99% with alternating temperatures of 15 and 25 C with concurrent dark and light periods. Germination was significantly higher when temperature was alternated, compared with a constant 15 or 25 C. Alternating light (8 h) and darkness (16 h) with either alternating or constant temperature significantly increased germination when compared with germination in the dark. After 9 yr, seed germinated over 41% under optimum conditions. Dicamba (3,6-dichloro-o-anisic acid) at 2.2 kg/ha reduced common yarrow infestations 90 to 95% in 3 of 4 yr, and 3,6-dichloropicolinic acid3,4 (designated D-290 in this paper) at 0.6 to 2.2 kg/ha controlled yarrow 90 to 100%. Yields on plots treated with D-290 at 0.6 kg/ha were significantly higher than those on plots treated with all rates of dicamba. Dicamba caused injury to grass and reduced its yield. Triclopyr [(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid at 3.4 kg/ha was not effective on yarrow.

Greenhouse studies showed that common cocklebur (Xanthium pensylvanicum Wallr.), green foxtail (Setaria viridis (L.) Beauv.), sunflower (Helianthus annuus L.), and velvetleaf (Abutilon theophrasti Medic.) were selectively controlled with postemergence herbicides in soybeans (Glycine max (L.) Merr. ‘Ford’). In the field the control of velvetleaf in soybeans was obtained by applying a postemergence-directed herbicide when soybeans were 15 cm tall and had the second trifoliolate leaf present. Postemergence-directed herbicides did not adequately control grass weeds. It was necessary to use a preplant or preemergence herbicide for grass control. Mechanical removal of lower leaves of soybean plants grown in the greenhouse significantly decreased yield. However, with field-grown ‘Amsoy’ soybeans mechanical removal of cotyledons, unifoliolate, and the first trifoliolate leaves did not reduce yield.

The fate of 3,4-dichloroaniline (DCA), a major metabolite of the herbicide propanil (3′,4′-dichloropropionanilide), in rice (Oryza sativa L.), soil, water, and aquatic organisms was determined in rice-paddy microecosystems. Soil, treated with 10 ppm DCA, was placed in glass chambers, planted to rice, then flooded when the rice reached the two-leaf stage. After flooding, four species of aquatic organisms were added. The concentration of DCA and metabolites in soil, rice, water, and aquatic organisms was determined over a period of time. A maximum of 2.8% of the total radioactivity applied to soil desorbed or leached into water. DCA recovered from water decreased from 12 to 1% of the total radioactivity in water between 1 and 30 days after flooding. Between 10.5 and 18.5% of the radioactivity remaining in soil at the end of the experiments was extractable. Of the radioactivity recovered, between 5 and 11% was DCA, and up to 6 to 19% was 3,3′,4,4′-tetrachloroazobenzene (TCAB), these percentages being dependent on exposure time. Rice accumulated 0.5% or less of the total radioactivity in soil. Only 35 to 55% of the accumulated radioactivity was extractable. Very small amounts of radioactivity were accumulated by aquatic organisms.

Tubers of yellow nutsedge (Cyperus esculentus L.) were collected over a 2-yr period to investigate the variation in abscisic acid (ABA) and total phenols throughout the year. The amount of ABA increased gradually from the end of the summer to November when it reached the highest level (6.81 μg/g fresh wt of tubers). This coincided with the onset of dormancy of the tubers in the field. In April, when a maximum of tubers showed sprouting, no free ABA was detected in tuber extracts. These data seem to indicate that free ABA is, in part at least, responsible for the dormant state of tubers. No obvious relation was seen between the state of dormancy of the tubers and their total phenolic content. It is unlikely that the phenolics as a group have one specific role in regulating dormancy of the tubers, but is possible that individual classes, or individual phenols, may possess significant activity.

Foliar absorption of picloram by broom snakeweed, a rangeland shrub, was investigated. Picloram uptake into leaf, axillary bud, and stem tissues was similar. In addition, picloram uptake by leaf tissue from greenhouse- and field-grown broom snakeweed did not differ. Picloram accumulated rapidly and absorption saturated between 15 min and 1 h of application; no further absorption occurred through 72 h with maximum uptake ca. 15% of applied picloram. Picloram content increased linearly with increasing external picloram concentration, implying that movement of the herbicide across the cuticle is via diffusion. Absorption was dependent on relative humidity and temperature with the greatest uptake at 94% relative humidity and 35 C, respectively. Absorption was pH dependent; picloram absorption was greatest at pH 4 and least at pH 8. In addition, picloram absorption was less at pH 3 compared to pH 4. These results provide evidence that picloram is absorbed across the cuticle via simple diffusion and absorption is dependent on environmental conditions and solution pH at and following application.

Three Italian Lolium weed populations, one susceptible and two resistant to diclofop, were characterized by the technique of inter simple sequence repeats (ISSR). The goal of this study was to taxonomically identify these Lolium populations as well as to evaluate evidence for introgression of ISSR fragments from Festuca and the potential role of this introgression in the diclofop response. ISSR analysis confirmed the genomic background of the weed populations to be consistent with that of Lolium. However, the great range of variation in ISSR banding patterns highlighted that the three ryegrass accessions are mixed populations made up of individuals resulting presumably from intrageneric and intergeneric hybridization in the Lolium–Festuca complex. Two Festuca genus-discriminating and 20 Festuca species-discriminating ISSR markers were screened among all the three ryegrass populations. The resistant Tuscania population carried the highest percentage of Festuca genome (16.8%) followed by the resistant Roma (13.6%) and susceptible Vetralla (7.6%) populations. On the basis of these data some influence of Festuca genome in diclofop resistance levels of studied ryegrass populations could be hypothesized.

Experiments were conducted to determine the influence of various factors on asulam {methyl[(4-aminophenyl)sulfonyl] carbamate} toxicity to flax (Linum usitatissimum L.) and wild oats (Avena fatua L. # AVEFA). Asulam toxicity to both flax and wild oats generally increased as temperature, humidity, and soil moisture increased after treatment. Octoxynol {α-[p-1,1,3,3-tetramethyl butyl phenyl]-ω-hydroxypoly(oxyethylene)} in the spray solution increased asulam toxicity to both species in all environments. Octoxynol and trimethylenonypolyethoxyethanol (WK) enhanced asulam toxicity more than other adjuvants evaluated. Asulam toxicity to both flax and wild oats increased as octoxynol concentration in the spray increased. Flax tolerance to asulam generally increased with flax height at treatment. ‘Flor’ flax was the most asulam susceptible of six cultivars evaluated. A 2-mm simulated rainfall within 3 or 6 h after asulam treatment reduced toxicity to wild oats and flax, respectively.

Field and laboratory experiments were conducted with unicorn-plant to determine conditions required for germination and to measure seed production. Field-grown plants produced an average of 122 pods/plant with an average of 71 seed/pod. The highest percent germination from seed harvested in 1980 occurred following a 2-week prechill treatment of 4 C. Germination increase was greater by removing the seed coat and the membrane enclosing the embryo than by removing the seed coat alone. Germination of seed from all pod compartments was similar. Aqueous extracts of unicorn-plant testa, leaf, stem, root, and exocarp were inhibitory in petri dish bioassays to cotton radicle growth. Extracts of stem, root, and exocarp were inhibitory to wheat radicle growth, and extracts of endocarp, leaf, and exocarp were inhibitory to unicorn-plant radicle growth. Seed buried in the field 10 cm deep for 1 to 8 months showed increased germination over time. Germination was lower when seed were stored at 4 C for 1 to 8 months in a soil having 25% (v/v) water.

Acetolactate synthase (ALS)-inhibiting herbicide carryover in soil can severely affect sugarbeets grown in the year(s) following application. Two newly developed imidazolinone-resistant (IMI-R) sugarbeet somatic cell selections (Sir-13 and 93R30B) were examined for magnitude of resistance and extent of cross-resistance to other classes of ALS inhibitors and compared to a previously developed sulfonylurea-resistant (SU-R) selection, Sur. In vitro shoot culture tests indicated Sir-13 resistance was specific to imidazolinone (IMI) herbicides at approximately a 100-fold resistance compared to the sensitive control sugarbeet. Sur was 10,000-fold resistant to the sulfonylurea (SU) herbicide, chlorsulfuron, and 40-fold resistant to the triazolopyrimidine sulfonanilide (TP) herbicide, flumetsulam, but not cross-resistant to the IMI herbicides. 93R30B was selected for IMI-R from a plant homozygous for the SU-R allele, Sur, and displayed similar in vitro SU-R and TP-R as Sur, but also displayed a very high resistance to various IMI herbicides (400- to 3,600-fold). Compared to the sensitive control, Sir-13 was 300- and > 250-fold more resistant to imazethapyr and imazamox residues in soil, respectively. Response by whole plants to postemergence herbicide applications was similar to that observed in shoot cultures. Sir-13 exhibited > 100-fold resistance to imazethapyr as well as imazamox, and 93R30B showed > 250-fold resistance to both herbicides. 93R30B showed great enough resistance to imazamox to merit consideration of imazamox for use as a herbicide in these sugarbeets. Sir-13 showed a two- to threefold higher level of resistance in the homozygous vs. heterozygous state, indicating that like most ALS-inhibitor resistance traits, it was semidominantly inherited.

Root applications of (2,4-dichlorophenoxy)acetic acid (2,4-D) at concentrations of 2.5 × 10−8M or higher inhibited growth of emersed parrotfeather (Myriophyllum brasiliense Camb.). There was little acropetal movement after applications of 1.1 × 10−5M 2,4-D-1-14C to the roots of emersed parrotfeather. When the metabolic inhibitor dinitrophenol at concentrations of 10−3 or 10−4M was root-applied concomitantly with 10−8M 2,4-D-1-14C, there was an acropetal movement of radioactivity in the transpiration stream to the plant shoot. Basipetal movement occurred in the phloem after applications of 2.2 μg 2,4-D-1-14C to mature leaves in the shoot center of emersed parrotfeather.

The total quantity and concentration of six herbicides, isopropyl m-chlorocarbanilate (chlorpropham), 2-chloro-4-(ethylamino)-6-(isopropylamino-s-triazine (atrazine), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor), 3-amino-2,5-dichlorobenzoic acid (chloramben), and (2,4-dichlorophenoxy)acetic acid (2,4-D), in unaerated, aqueous solutions absorbed by seeds of 11 soybean (Glycine max (L.) Merr.) strains were measured. Mechanism of movement of the herbicides from the aqueous solutions to the seeds in the experimental procedure employed was diffusion. Total quantity and concentration of herbicide found in the seeds differed significantly for both herbicides and soybean strains. Total quantity of herbicide absorbed was determined by total oil and percent oil of the seeds. The capacity of the seeds to absorb a given herbicide was more closely related to percent oil of the seeds than to total oil of the seeds. The emergence and seedling shoot weight of ‘Cutler’ soybeans were not affected appreciably by concentrations of linuron, atrazine, and chloramben (potassium salt) but were reduced by high concentrations of chlorpropham and alachlor and relatively low concentrations of 2,4-D (potassium salt) in the seeds.

The effect of 1.0 ppmw fluridone {1-methyl-3-phenyl-5-[3-trifluoromethyl)phenyl]-4(1H)-pyridinone} on growth of American pondweed (Potamogeton nodosus Poir.) and sago pondweed (Potamogeton pectinatus L.) was examined in plants kept in darkness or under various numbers of 12-h photoperiods. When plants were exposed to 1.0 ppmw fluridone for 1 to 10 12-h days, no stunting of American pondweed occurred until 21 days after treatment. Thirtythree days after treatment, plants that had received 4 to 10 days' exposure were most stunted. Sago pondweed was slightly more susceptible than American pondweed (87% and 50% reduction in length, respectively) 37 days after a 10-day exposure. Chlorophylls a and b were significantly lower in both species 14 days after all fluridone treatments. American pondweed plants exposed to fluridone continuously (1.0 ppmw) for 15 days, but given 0, 3, 6, 9, 12, or 15 12-h days were stunted only after having received at least six photoperiods. Stunting in sago pondweed was only slightly light-dependent. Neither species absorbed significantly more 14C-labeled fluridone after 2, 4, or 14 photoperiods compared to plants kept in darkness for the same time.

Interactions between carbamate and growth regulator herbicides were antagonistic both in whole plants and in plant segments. When combinations of isopropyl m-chlorocarbanilate (chlorpropham) and (2,4-dichlorophenoxy)acetic acid (2,4-D) were applied to the foliage of either redroot pigweed (Amaranthus retroflexus L.) or pale smartweed (Polygonum lapathifolium L.), the severe twisting effects of 2,4-D were greatly reduced. This interaction did not involve differential movement or metabolism of either herbicide. The induced elongation of soybean hypocotyl sections by the three growth regulators 2,4-D, 3,6-dichloro-o-anisic acid (dicamba), and 4-amino-3,5,6-trichloropicolinic acid (picloram) was inhibited in the presence of either chlorpropham or S-ethyl dipropylthiocarbamate (EPTC). Similarly, curvature tests using soybean (Glycine max (L.) Merr.) hypocotyl sections showed the curvature induced by the growth regulators to be almost completely eliminated by the presence of the carbamates.

The uptake and release of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) by green sunfish (Lepomis cyanellus Raf.) were measured during a 3-week exposure to either non-labeled or symmetrically ring-labeled 14C-simazine. Exposure was by feeding (3 and 10 mg/kg body wt) or bath (1 and 3 ppm). To determine the retention of simazine, treated fish remaining after exposure and sampling were placed in fresh water for 4 weeks. This water was changed weekly. Fish in the bath absorb simazine in amounts directly proportional to the concentration in the water: i.e., 0.95 and 2.29 ppm total residue after 3 weeks exposure to 1.0 and 3.0 ppm, respectively. Little or no simazine was found in feed-exposed fish 72 hr after feeding. Almost all of the residue was in the viscera. No simazine residue was detected in fish from the water bath exposure after they had been in fresh water 7 days.

The release of 3-amino-2,5-dichlorobenzoic acid (amiben), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), isopropyl m-chlorocarbanilate (chlorpropham), S-ethyl dipropylthiocarbamate (EPTC), and 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) from excised soybean (Glycine max (L) Merr., var. Chippewa) roots following uptake of the herbicides from solutions for 1 hr was studied. Rates of release of herbicides into water were rapid with at least 30% of that taken up being released during the first 30 min. Herbicide X time and herbicide X concentration interactions were highly significant. In most instances, slow release continued for 4 hr, which was the duration of the experiment. Use of herbicide or nutrient solutions as release solutions did not significantly change the amounts of herbicides released. It was concluded that herbicide molecules released after 1 hr uptake were those that had diffused out from free space rather than those released from uptake or adsorptive sites.

Scarification of freshly harvested redweed (Melochia corchorifolia L.) seed for 15 to 30 s in an electric scarifier equipped with 100- to 120-grit emery cloth resulted in the best germination. Scarified seed germinated best at 35 and 40C. At 10 and 45C there was no germination even after 7 days. Seven days after planting in silt loam soil there was 80 to 90% emergence of redweed from depths of 1 to 5 cm, whereas no emergence was observed from depths of 0, 8, or 10 cm.

Detached leaves and whole plants of quackgrass [Agropyron repens (L.) Beauv. # AGRRE] were used to study uptake and translocation of butyl esters of 14C-fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, with or without additional adjuvants. In the absence of adjuvants 3.2% of applied radioactivity entered detached quackgrass leaves by 6 h, and at the end of 24 h, 6.0% had penetrated. The presence of additives increased uptake by leaves significantly. In the presence of the nonionic surfactant Agral (nonyl phenol ethoxylate) at 0.2% (v/v) or the oil-additive Actipron (self-emulsifying adjuvant oil) at 2.0% (v/v), 17.2 and 12.9% of applied radioactivity, respectively, entered the leaves by 24 h. Evidence of dependence of phloem translocation of the radioactivity on source-sink relationships of the plant was obtained in the studies with whole plants. Translocation measured up to 7 days after treatment showed that radioactivity was concentrated in areas such as young developed leaves, young stems, and rhizome apices. Rhizomes appear to be major sinks for the accumulation of radioactivity and at 7 days 0.5% of applied radioactivity was found there. In wholeplant experiments the two adjuvants either individually or in mixture increased the uptake of 14C-fluazifop significantly. However, a corresponding increase in basipetal translocation was found only in one experiment. Much of the increased activity that had entered the leaves in the presence of adjuvants was found to have moved to areas distal to the treated zone or remained within the treated zones. In all experiments, applied 14C was not fully recovered. Evidence of significant volatility losses from treated surfaces was obtained and it is thought that this may be the main reason for the inability to recover all of the applied activity.

Weeds pose a great problem to farmers worldwide, and controlling weeds demands a high input cost for herbicides and labor. Because of current environmental regulations, a limited number of herbicides are commercially available (with limited modes of action) to control weeds. Smoke water and the biologically active compounds isolated from smoke affect seed germination in a significant way. Smoke water (SW) and karrikinolide (KAR1, the germination stimulant isolated from smoke) have been tested extensively for their ability to promote seed germination in a vast array of plant species. In addition to KAR1, a germination inhibitor, trimethylbutenolide (TMB), was also isolated from plant-derived smoke. The effects of SW, KAR1, and TMB were tested on five major weed species of South Africa: fleabane, hairy wild lettuce, bugweed, spilanthes, and fameflower. Seeds of these weed species were subjected to 16/8 h light/dark conditions or to constant dark conditions at constant temperatures of 20, 25, 30 C and alternating 30/20 C. SW and KAR1 significantly increased germination, whereas TMB significantly inhibited germination of these weed species. Furthermore, TMB treatment reduced the amylase activity of the tested weed seeds compared with the water control. These results indicate the possibility of manipulating germination of certain weed seeds by SW, KAR1, and TMB. Thus, smoke and smoke-isolated compounds could potentially be used in new weed management strategies.