Susceptible and resistant ecotypes of Canada thistle (Cirsium arvense L.) were grafted in various combinations of stock and scion to determine if the activity of 3-amino-l,2,4-triazole (amitole) was altered by passage through the plant tissue. It appeared that the differential susceptibilities of ecotypes of Canada thistle were not caused by a change in the activity of amitrole.

Terbacil (3-tert-butyl-5-chloro-6-methyluracil), diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], and metribuzin [4-amino-6-butyl-3-(methylthio)-as-triazin-5(4H)-one] controlled palmer amaranth (Amaranthus palmeri S. Wats. ♯ AMAPA) in established alfalfa (Medicago sativa L.) when applied after first harvest. However, these same herbicides did not control palmer amaranth when applied early-season in March. Alfalfa forage yields were increased when palmer amaranth was controlled. Residue levels of terbacil and its metabolites in alfalfa forage from plots treated postharvest with 1.1 kg/ha of terbacil were well below the 5-ppm tolerance level established for terbacil in alfalfa. There was some chlorosis of alfalfa foliage following the postharvest use of the 1.1 kg ai/ha of terbacil. There was also a yield reduction of alfalfa in two of the six experiments (one from a March and one from a June application) where 1.1 kg ai/ha of terbacil was evaluated.

Field research to determine the influence of weed control systems in winter barley on subsequently no-till-planted grain sorghum was conducted from 1985 to 1987 in northwest Georgia. Herbicide treatments applied to fully tillered winter barley included 2,4-D, dicamba, metribuzin, oryzalin, oryzalin plus metribuzin, fluorochloridone, or thiameturon. None of these herbicides affected barley grain yields compared to nontreated plots. Treatments containing oryzalin reduced johnsongrass fresh weights in the subsequently planted grain sorghum. Oryzalin plus metribuzin, in 1 of 2 yr, resulted in higher seed yields of subsequently planted grain sorghum compared to the other treatments except for oryzalin used alone. Treatments containing paraquat plus propazine plus metolachlor applied to grain sorghum provided good weed control when averaged across barley treatments and resulted in the highest grain sorghum yield. No grain sorghum injury from herbicides used in the previous winter barley crop was observed.

The morphological and physiological response of the slender oat (Avena barbata Pott ex Link # AVEBA) to the herbicides barban (4-chloro-2-butynyl 3-chlorophenylcarbamate) and difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) in conjunction with decreased water availability was determined for seven populations, representing three ecotypes, under greenhouse conditions. Generally, within the range of sublethal herbicide doses, with increasing herbicide rates, phytotoxicity ratings increased, but plant dry weight, tiller height, and number of spikelets were decreased. Also, the number of juvenile tillers decreased, while that of fertile tillers increased. Flag leaf area increased and flowering was delayed. The ratio of number of spikelets to plant dry weight and seed weight was influenced the least. Under the highest rates of difenzoquat, the within-plant variance of spikelet number decreased, indicating that there may have been a more equal partitioning of resources amongst tillers for spikelet production. The general influence of water stress was to amplify the effect of the herbicide. For example, the dry treatment reduced dry weight and tiller height, and delayed flowering. Within a particular herbicide treatment, the effect of the water stress was to cause reduced within-plant variance for days to flowering, flag leaf area, and number of spikelets. Three reactions were observed that could have helped buffer decreases in spikelet production: 1) An increased fraction of the dry weight of the plants was partitioned into the spikelets at the expense of other vegetative matter, 2) the increased leaf area of the primary tiller may have helped counterbalance any reduction in photosynthesis caused by herbicide action, and 3) an increased number of juvenile tillers was converted into fertile tillers resulting in an increased number of mature tillers. These data indicate that the slender oat has a remarkable “phenotypic plasticity,” which enables it to maintain reproductive structures under sublethal herbicide doses.

Chemical fallow with 2,2-dichloropropionic acid (dalapon) reduced the yield of non-seeded perennials more than mechanical fallow with sweep blades in the year of treatment. However, plants derived from seed left at the soil surface resulted in greater yields of nonseeded perennials on chemical than on mechanical-fallow plots the year following treatment. Each fallow method increased annual herbage yields the year after treatment as compared with directly-seeded plots. Litter was greatly reduced in the year of and in the year after mechanical fallow. However, the amount of litter on the chemical fallow plots was very high in the year of treatment and declined in the succeeding year. Success of seeding crested wheatgrass [Agropyron desertorum (Fisch, ex Link) Schult.] was slightly better after mechanical than after chemical fallow. Yield of crested wheatgrass in the year after planting was about the same for the mechanical fallow and the higher rate (10 lb/A) of dalapon. There was more available soil moisture to a depth of 30 inches in fallowed than in non-treated plots; but the small amount of moisture saved by fallow probably is immaterial to seeding success.

Six-week-old honey mesquite [Prosopis glandulosa (Torr.) var. glandulosa] seedlings were treated with various concentrations of ethephon (2-chloroethylphosphonic acid) and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] alone and in combinations to determine effect on stem mortality under greenhouse conditions. Ethephon alone at 0.05 g/L brought about defoliation and a reduction in xylem tissue formation but did not affect the histological development of the stem tissue. Treatment with 2,4,5-T alone at 3.2 g/L resulted in 40% stem mortality along with the formation of abnormal xylem tissue of reduced thickness. A combination of ethephon (0.05 g/L) and 2,4,5-T (3.2 g/L) significantly increased mesquite mortality. This was associated with a further reduction in xylem thickness, abnormal development of the xylem, abnormal positional relationships of vascular tissues, and initiation of adventitious roots. This study showed that ethephon in combination with 2,4,5-T was more effective than either treatment alone in promoting the disruption of the tissue systems of the stem and in increasing control of mesquite seedlings.

One method that appears promising for the treatment of Eurasian watermilfoil in areas of high water exchange is the use of herbicide-impregnated granules. Experiments were conducted using liquid triclopyr-triethylamine and granules impregnated with triclopyr-triethylamine to test this theory. Uniform, multistemmed Eurasian watermilfoil plants were selected for these experiments. Plants were treated in clear acrylic cylinders containing 7 L of water with 0.5 mg/L triclopyr as the liquid triethylamine plus 20 kBq 14C-triclopyr or blank granules impregnated with triclopyr triethylamine plus 20 kBq of 14C-triclopyr. Plants were harvested 6, 12, 24, 48, 96, and 192 h after treatment (HAT) and the radioactivity in the apical meristems, remaining shoot and root was determined with sample oxidation and liquid scintillation spectroscopy. There were no significant differences in overall herbicide absorption by Eurasian watermilfoil following liquid and granular triclopyr treatments; however, differences were observed between plant parts. Apical meristems accumulated the most radioactivity, whereas roots accumulated very little radioactivity following liquid treatment. Granular applications resulted in 7.5 times more radioactivity in the Eurasian watermilfoil roots then the liquid triclopyr application; therefore, long-term control of well-established Eurasian watermilfoil plants could improve with granular applications, especially in areas where rapid herbicide dilution could be an issue.

A method for isolating roots of a growing plant was devised. The technique allows treatment of an isolated portion of the root system without disturbance or injury to the untreated root mass. A specially designed planter-box was used to induce natural separation of the root system in 3 to 4 weeks. Weeping willow (Salix babylonica L.) seedlings were used to test the performance of dichlobenil (2,6-dichlorobenzonitrile), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), sodium hydroxide (NaOH), and copper sulfate (CuSO4 • 5H2O) in reducing the viability of treated roots. A tetrazolium chloride assay was used to determine the difference in viability of the treated roots. Copper sulfate and paraquat-treated plants produced symptoms of systemic injury.

About 25 ppm of 4-amino-3,5,6-trichloropicolinic acid (picloram) usually were detected on grass, primarily buffalograss (Buchloe dactyloides (Nutt.) Engelm.) and blue grama (Bouteloua gracilis Willd. ex HBK Lag ex Griffiths), immediately after application of 0.28 kg/ha picloram + 0.28 kg/ha (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in northwest Texas. Less than 1 ppm of picloram usually was detected in grass tissue 30 to 60 days after treatment. At one location, detectable picloram increased in grass tissue from 32 to 60 days after application. Increases of picloram in aerial grass tissue were attributed to root uptake during a flush of vegetative growth. Picloram dissipation from grasses was not affected by irrigation to runoff at 10, 20, or 30 days after application. Detectable picloram was reduced by 93% in herbaceous, broadleaf species by 30 days after application. Treated sand shinnery oak (Quercus havardii Rydb.) leaves at the soil surface caused a slight increase of picloram in surface litter.

After land was plowed in the spring and prepared for planting, yellow nutsedge (Cyperus esculentus L.) was allowed to develop to heights of 10 to 12 and 20 to 25 cm. Either glyphosate [N-(phosphonomethyl)glycine] or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) was applied to emerged yellow nutsedge and other annual weeds at rates of 0.5, 1, 2, and 4 kg/ha. Half of the plots were double-disked 3 days after herbicide applications, and then all plots were planted with alfalfa (Medicago sativa L. ‘Cayuga’). Disking alone and application of glyphosate or paraquat alone did not satisfactorily control all weeds. However, the combination of a herbicide and disking controlled weeds enough to allow excellent establishment of alfalfa. In the year after establishment, the first cutting yields from the better combination treatments ranged from 3000 to 4400 kg/ha, which is normal for mid- to late-summer plantings in the region. Glyphosate was better than paraquat for control of grass weeds. Paraquat approached glyphosate in effectiveness when a supplemental disking treatment was added. Disking was as effective as the herbicide treatments for control of yellow nutsedge but not for control of broadleaf or annual grass weeds.

Field experiments were conducted to evaluate placement techniques for preemergence applications of pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] in grain sorghum [Sorghum bicolor (L.) Moench.]. The first technique consisted of row shields mounted behind the planter units. Shields maintained an untreated strip over the crop drill and allowed successful crop establishment with pendimethalin at 1.1 kg ai/ha, despite a simulated, intense rainfall of 3.8 cm within 24 h after planting. A second technique, which consisted of a special nozzle arrangement, was evaluated in no-till grain sorghum. The nozzle arrangement allowed a broadcast herbicide application but maintained an untreated strip over the crop drill. No stand reductions occurred using this technique at pendimethalin rates of 1.1 and 2.2 kg/ha. In a growth chamber experiment, preemergence applications of pendimethalin severely injured grain sorghum when the soil was wet at the time of emergence, but injury was reduced under hot, dry conditions.

Maximum activity of isocitric lyase (EC 4.1.3.1) was reached at 24 hr incubation of afterripened (nondormant) prickly sida (Sida spinosa L.) seed. Enzyme activity declined gradually with incubation times in excess of 24 hr. Actinomycin D (Act D) at 5 μg/ml had essentially no effect on 24-hr germination but inhibited development of isocitric lyase activity 83%. Cycloheximide (CH) at 10 μg/ml inhibited 24-hr germination of punctured seed only 7% but inhibited development of isocitric lyase activity 76%. Seed incubated in water 12 hr before being transferred to Act D at 5 μg/ml for an additional 12 hr did not escape sensitivity to the antibiotic. Isocitric lyase activity was inhibited when assayed at 24 hr total incubation. In the reverse experiment, seed incubated in Act D 12 hr before being transferred to water, isocitric lyase activity at 24 hr was not affected. Apparently prickly sida seed lacked a performed mRNA for isocitric lyase and transcription and translation of the mRNA occurred shortly after initiation of radicle protrusion (~8 hr).

Five varieties of 3-month-old citrus rootstocks were grown for 1 month in nutrient solution containing 0, 10-3, 10-4, or 10-5 M of norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3 (2H)-pyridazinone] to assess the effect of this herbicide on growth and chlorophyll levels. The uptake, translocation, and metabolism of root-applied 14C-norflurazon was also examined in these rootstocks. Norflurazon treatment reduced chlorophyll level and lowered overall growth in sour orange (Citrus aurantium), Swingle (Poncirus trifoliata × C. paradisi), Milam (C. jambhiri), and Cleopatra mandarin (C. reshni) rootstocks. Herbicide treatments had little or no effect on chlorophyll levels or growth in Carrizo (C. sinensis × P. trifoliata). In Cleopatra, unlike in other rootstocks, leaf chlorosis was evident only along the midrib and major veins. Herbicide treatment reduced leaf flush (leaf production) in Swingle but not in other rootstocks. By the end of a 4-week treatment period, total absorption of 14C-norflurazon was greater in Swingle than in the other rootstocks. 14C-norflurazon detected in the roots (excluding taproot) of Swingle was greater than in the other rootstocks. The amount of 14C-norflurazon translocation to the foliage was limited in all rootstocks. Stem and taproot also contained only a small amount of 14C-norflurazon. Leaf extracts of all five rootstocks contained no parent compound, but up to 90% of recovered 14C was identified as 14C-norflurazon in root extracts. Differences in the uptake, translocation, and metabolism of norflurazon among citrus rootstocks were small and did not appear to explain their differential sensitivity to this herbicide.

Key metabolic enzymes and germination were studied in developing and mature, dormant and nondormant prickly sida (Sida spinosa L.) seeds. Isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, fructose-1,6-diphosphatase, and phosphofructokinase activities were determined in developing and mature prickly sida seeds. Developing seeds less than 7 days after anthesis and at 17 days or greater after anthesis were unable to germinate. The 7-day-old seeds lacked all but fructose-1,6-diphosphatase activity. The 17-day-old seeds demonstrated all enzyme activities but failed to germinate because dehydration had occurred and seeds were unable to imbibe sufficient water without an afterripening period. Comparison of enzyme activities of dormant and nondormant seeds on incubation showed that only glucose-6-phosphate dehydrogenase was considerably different within the first 8 h of incubation. Nondormant seeds had considerable glucose-6-phosphate dehydrogenase activity before germination (radical protrusion at 8 h), suggesting an active pentose phosphate pathway.

Crystallization of methyl m-hydroxycarbanilate m-methyl-carbanilate (phenmedipham) occurred from aqueous emulsions of the commercial formulation when dilutions exceeded one part of the formulation to 30 parts water. Dilutions greater than 1 to 30 accelerated crystallization and increased the quantity of phenmedipham that crystallized out. Mechanical agitation increased the rate of crystallization during the first 12 hr after initial mixing. Low water temperature increased the rate of crystallization and total amount of phenmedipham that crystallized out. Phenmedipham crystallization was not altered by water hardness or pH over the range 4.0 to 8.0. Simulated refilling of a partially empty spray tank before adding formulated phenmedipham produced considerable crystallization, whereas adding formulated phenmedipham before adding water minimized crystallization. The solvent used in the commercial formulation to dissolve phenmedipham is partially soluble in water. The partitioning of this solvent into the aqueous phase of the emulsion explains crystallization of phenmedipham.

A new machine consisting of a detachable hopper of containerized granules with a preselected circular orifice to regulate flow of granules, and a revolving hollow-cone spreader turned by an electric motor, was tested. Flow of herbicide granules at typical use rates was linearly correlated with orifice diameter. Coefficients of determination for flow rates of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine], and norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3 (2H)-pyridazinone] were 0.96 or greater. Based on patterns of distribution of commercial trifluralin granules parallel and perpendicular to a linear path, the machine could be used to apply herbicide granules in row crops. Control of johnsongrass [Sorghum halepense (L.) Pers. # SORHA] with alachlor plus oryzalin [4-(dipropylamino)-3,5-dinitrobenzenesulfonamide] applied preemergence (pre) as sprays and granules did not differ significantly in soybean [Glycine max (L.) Merr. ‘Forrest′]. Trifluralin granules applied preplant incorporated (ppi) at 1.1 kg ai/ha controlled 80 to 95% of the johnsongrass and doubled soybean yield compared to the cultivated control plot. Norflurazon plus alachlor pre at 1.7 to 2.2 plus 2.2 to 3.0 kg ai/ha controlled annual grasses and prickly sida (Sida spinosa L. # SIDSP) equally with sprays and granules.

n-Pentane was used to extract 3-(m-trifluoromethylphenyl)-1,1-dimethylurea (fluometuron) from soil-water samples. The microgram quantity of fluometuron in the n-pentane was measured at a wavelength of 242 mμ with an ultraviolet spectrophotometer and this measurement related to the fluometuron concentration in the soil-water sample. No measurable interference was noted in the n-pentane after the extraction of fluometuron from the soil-water samples. The procedure was developed for extracting and quantitatively determining fluometuron in soil-water samples.