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.

The potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram) was applied as soil, foliar, and soil plus foliar treatments to defoliated and non-defoliated huisache (Acacia farnesiana (L.) Willd) grown in the greenhouse. Soil applications of ⅛ lb/A were more effective than foliar treatments. However, soil or foliar applications at ½ lb/A were lethal on non-defoliated plants. Defoliated plants treated with ½ lb/A showed considerable regrowth, indicating that leaves were important for absorption and movement of the herbicide into stem and root tissues. Plants treated with ¼ lb/A of picloram and defoliated after 0, 4, 10, and 24 hr indicated that 24 hr were necessary to obtain maximum herbicidal effectiveness.

Picloram content was determined in the leaves, upper stem, lower stem, and roots by gas chromatographic analysis, 3, 10, and 30 days after treatment. Most of the picloram applied to foliage was found in and on the leaves 30 days after treatment. The upper stem contained several times more picloram than the lower stem. No detectable amounts of picloram were found in the leaves and upper stem 3 and 30 days after soil treatment. The concentration of picloram in roots from soil applications was similar to foliar treatments. Absorption and movement studies showed that a period of 24 hr was required to move lethal amounts of picloram into stem and root tissues of huisache after foliar treatments.

Results of studies with the herbicide 1-(3-chloro-4-methylphenyl)-3-methyl-2-pyrrolidinone (hereinafter referred to as BV-207) suggest that it interferes appreciably with photosynthesis. A concentration of 10-4 M of BV-207 almost completely inhibited fixation of labelled carbon dioxide by leaf disks of various plants. In addition, carbohydrates protected plants from the phytotoxic action of the chemical. BV-207 was considerably more toxic when plants received light after application of the herbicide, compared with those held in the dark. On the other hand, root growth was inhibited only slightly by BV-207.

Selective control of red sorrel (Rumex acetosella L.) in Kentucky bluegrass (Poa pratensis L.) seed fields was obtained with 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 7-oxabicyclo(2.2.1)-heptane-2,3-dicarboxylic acid (endothall), 3-amino-2,5-dichlorobenzoic acid (amiben), 2,3,6-trichlorophenylacetic acid (fenac), and 2,3,6-trichlorobenzoic acid (2,3,6-TBA). Kentucky bluegrass seed yields and germination were not significantly reduced by application of any of the herbicides in the fall even though rates higher than necessary for red sorrel control were used. Application of dicamba in the spring at more than 1/2 lb/A reduced Kentucky bluegrass seed yields and germination. Endothall reduced seed yields when applied in the spring at 4 or 5 lb/A.

Tracer studies employing 2,2-dichloropropionic acid (dalapon)-2-C14 and -Cl36 were conducted on barley (Hordeum vulgare L.), bean (Phaseolus vulgaris L.), and three hypostomatous species—zebrina (Zebrina pendula Schnizl.), coleus (Coleus blumei Benth.), and nasturtium (Trapoelum majus L.). Count data and radioautographic evidence showed that greater amounts of dalapon were absorbed and translocated at high (88 ± 3%) than medium (60 ± 5%) or low (28 ± 3%) post-treatment relative humidity (herein called R.H.). Also, greater uptake and translocation of C14 occurred in bean at 43 ± 1 C than at 26 ± 1 C post-treatment temperature, with constant R.H. and light conditions. Rate of droplet drying, and stomatal distribution and behavior, apparently contributed to the R.H. effect. Droplets dried less rapidly at high than at low R.H., thus prolonging the period of effective absorption. At low R.H., periodic rewetting of the droplet area enhanced absorption and translocation but never to the extent achieved with high ambient R.H. (in growth chambers) or in saturated atmosphere (polyethylene bagging in the greenhouse). High R.H. (95 ± 3%) favored stomatal opening in zebrina, and uptake of dalapon was greater through the abaxial than adaxial surface of leaf disks of zebrina, coleus, and nasturtium. Rewetting of droplets or high ambient R. H., however, promoted uptake through astomatous as well as stomated surfaces. Absorption and translocation were markedly greater in bean plants grown at 95 ± 3% R.H. than at 28 ± 3% R.H., both treated under high R.H. conditions. Thus cuticle hydration and ontogeny also were implicated in the R.H. phenomenon. Several solution additives also were studied in an attempt to substitute for the R.H. effect. At low R.H., a surfactant (X-77) markedly enhanced uptake of dalapon in bean, glycerol (a humectant) and hexadecanol (a filming agent) were less advantageous, and Plyac (a sticker-spreader) decreased penetration. Results of these studies aid in explaining the greater toxicity of dalapon in regions of high R.H. and, conversely, its sometimes erratic performance in drier climates. The results also confirm the distribution and accumulation patterns of dalapon absorbed by plants and the usefulness of an effective spray adjuvant in promoting foliar absorption.

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.

Residues of 2,3,6-trichlorophenylacetic acid (fenac) and 2,6-dichlorobenzonitrile (dichlobenil) were determined in irrigation water flowing over canal-bottom plots treated with the herbicides prior to the entry of water. Concentrations of fenac and dichlobenil in the first water to flow over the entire treated plots were 8.82 and 8.63 ppm, respectively. The bulk of the residues was transported from the plots in a very short time, and safe levels were reached after 1 hr of water flow. The dichlobenil burden, picked up by water as it flowed over the treated plot, was effectively reduced as the water passed over untreated canal soil downstream.

The depth of leaching of 3(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) in a Yolo sandy clay loam soil was altered by the various types—anionic, cationic, or nonionic—of surfactants. The effects of surfactants Aliquat 204 and Aliquat 221 on the leaching of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon), and diuron may reflect a sorption complex of the substituted urea herbicide, surfactant, and the soil. This sorption appears to be closely associated with the dilauryl portion of the surfactant molecule. Other surfactants of the Aliquat series containing lauryl, dioctyl, and distearyl substitutions had little or no effect on this sorption phenomenon.

In field experiments, corn (Zea mays var. Dixie 18) and Johnsongrass (Sorghum halepense) seeds were planted in Norfolk sandy loam soil and treated preemergence with 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) at 0, 2, 4, and 16 lb/A. In growth chamber studies, corn seeds were planted in flats of Independence loamy fine sand and treated pereemergence with atrazine at 0, 2, and 4 lb/A. In nutrient culture studies, corn was treated with 0, 2, 4, and 8 ppmw atrazine.

Treated plants of all species and rates tested usually were smaller than untreated plants and contained higher nitrogen percentages. Corn and Johnsongrass plants treated with high rates of atrazine always contained less nitrogen (mg/plant) than untreated plants. Atrazine-treated corn plants contained higher percentages of both 80% ethanol soluble and insoluble nitrogen than the checks. Percentage increases in both fractions were proportional to the rate of atrazine treatment. Nitrate percentages also were increased, but free ammonia content was not significantly affected.

Foliar and soil herbicidal treatments were made on creosotebush (Larrea tridentata (DC.) Cov.), tarbush Flourensia cernua DC.), and whitethorn (Acacia constricta Benth.) near Tombstone, Arizona, from 1957 to 1964. All herbicides were most effective when applied approximately 30 days after initiation of the summer rainy season. The herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were about equal in effectiveness, but the relative susceptibility of the individual shrubs to the herbicides varied with treatment conditions. The acetic form of 2,4,5-T generally was more effective than the propionic; propylene glycol butyl ether, iso-octyl, and tetrahydrofurfuryl esters more effective than pentyl. Foliar applications of 4-amino-3,5,6-trichloropicolinic acid (picloram) were most effective on whitethorn, intermediate on creosotebush, and least effective on tarbush. The most effective soil herbicidal treatments were 3-phenyl-1,1-dimethylurea (fenuron) and 3-(p-chlorophenyl)-1,1-dimethylurea (monuron). In general, effective control of dominant Chihuahuan Desert shrubs required 2 to 4 lb/A of 2,4-D or 2,4,5-T, 14 to 1 lb/A of picloram, or 2 lb/A of fenuron or monuron.

Differences in degree of seed dormancy were shown to exist both among and within the four varieties of wild oats (Avena fatua L. spp. fatua (L.) Thell.) occurring in natural infestations throughout southwestern Alberta. Among the varieties, pilosissima was the most dormant, intermedia was more dormant than vilis, and glabrata possessed about the same dormancy as intermedia. Dormancy was overcome more rapidly under dry storage in vilis and glabrata than in intermedia and pilosissima. Seed dormancy of most collections made in 1959 differed from that of collections made at the same locations in 1962, being both higher and lower by as much as 40% in either of the varieties vilis or intermedia. In seeds from plants grown as transplants at three sites, dormancy differed within varieties, but there was no consistent pattern of difference evident among sites.

The herbicide 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) was selective for sugar beets (Beta vulgaris L.). In preemergence treatments, sugar beets tolerated pyrazon at rates up to 6 lb/A, but at this level some mortality occurred. On the other hand, some weed species were susceptible to levels as low as 2 lb/A. Between emergence and the cotyledon stage, both beets and weeds were quite susceptible and the phytotoxicity of pyrazon increased with increasing temperature. In the late cotyledon stage, beets were resistant to pyrazon in aqueous suspension and partially susceptible to an oil-water suspension. Beets in the two to four-leaf stage tolerated an oil-water herbicidal combination, while lambsquarters (Chenopodium albium L.) and redroot pigweed (Amaranthus retroflexus L.) remained susceptible up to the six to eight-leaf stage. Rape (Brassica napus L.) was of intermediate susceptibility. In general, preemergence treatments were the most promising but could be replaced by postemergence treatments of pyrazon in an oil-water emulsion.

Measurements were made of plant toxicity and of several physical and chemical properties of spray solutions containing 1,1′-dimethyl-4, 4′-bipyridinium salt (paraquat) and either anionic, nonionic, or cationic surfactants. Surface tension and pH values were variable among 10 surfactant-paraquat mixtures and also at 0.1 and 1.0% surfactant concentrations, but neither showed any correlation with herbicidal activity on corn when all surfactants were considered. All four nonionic, both cationic, and two out of four anionic surfactants markedly enhanced paraquat toxicity at appropriate concentrations. Studies of UV absorbance of herbicide and surfactant solutions, alone and in combination, and adsorption of paraquat-C14 at solution-air interfaces indicate that significant interactions occurred between paraquat and the anionic surfactants. Foliar toxicity studies offered substantiating evidence of such interactions; however, the degree or lack of enhancement of paraquat toxicity was strongly influenced by plant species (corn vs. bean) and the type and concentration of surfactant. No surfactant-paraquat combinations studied were less effective than ⅛ oz/A of paraquat used alone.

Astragalus miser Dougl., var. oblongifolius (Rydb.) Cronq. was analyzed for seasonal and physical distribution of its contained poison. Small chickens (Gallus domesticus, Arbor Acre X Vantress hybrids) and cattle (Bos taurus, Hereford) were used as test animals. The poisonous compound was extracted from dried plants with 95% ethanol, evaporated and redissolved in water, then semi-purified by several extractions with chloroform for toxicological studies. The poison was found primarily in the green leaves. The plants were very poisonous until they began drying in August. Once leaves became bleached at senescence, toxicity disappeared. Plants treated with the triethylamine salt of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and the alkyl amine salts of 2-(2,4,5-trichlorophenoxy)-propionic acid (silvex) were less poisonous to cattle than untreated plants. Acute poisoning in chickens was characterized by depression, accelerated heart action, followed by congestion of lungs, cardiac insufficiency, paralysis, and heart failure. Chronically poisoned birds exhibited the same syndrome but sustained more severe liver damage.

Amitrole (3-amino-1,2,4-triazole) is absorbed and actively bound to non-physiological sites in Salmonella typhimurium. Accumulation of amitrole is inhibited by purines; but the effect does not seem to explain adenine protection against growth inhibition by amitrole. Guanine, xanthine, and hypoxanthine cannot replace adenine in growth protection but do inhibit accumulation of amitrole in the bacterial cells.

Satisfactory selectivity of 4-chloro-2-butynyl m-chlorocarbanilate (barban) for the control of wild oats (Avena fatua L.) in spring wheat was obtained when it was applied from 4 to 14 days after emergence of wild oats. Following this period, the effectiveness and selectivity declined rapidly. Depending on the season, this period of maximum efficiency represented the following growth stages of wild oats; 1 to 3-leaf stage in 1960, 1½ to 3½-leaf stage in 1961, and 1½ to 2½-leaf stage in 1962. Injury to wheat was most pronounced during a period beginning about 15 days after crop emergence and continuing for several weeks. This pattern of wild oat control and wheat susceptibility was virtually identical over the 3-year period even though growing conditions varied considerably. This suggests that days after emergence may be at least as reliable as leaf stages as an index for the proper timing of barban treatments and would be more easily determined under practical field conditions. If leaf stages are used, then spraying should not be recommended later than 2½-leaf stage, since in some years, wild oats will have reached resistant stages. Furthermore, it may be desirable to apply barban early, perhaps even before all the plants are fully in the 2½-leaf stage. When wild oats reach the 2-leaf stage, it may be too late, at least in years of abundant moisture.

The herbicidal activity of potassium azide and calcium cyanamid, applied singly and in combination, was evaluated in greenhouse and field experiments. In the greenhouse, the combinations were synergistic against several plant species including yellow nutsedge (Cyperus esculentus L.) and crabgrass (Digitaria sanguinalis (L.) Scop). The combinations also were synergistic in two field experiments at different locations. In the field, the combinations reduced the number of weed seeds germinating from treated soil over a 6-month period; potassium azide or calcium cyanamid applied singly were not effective. In the laboratory, calcium cyanamid reduced the rate of disappearance of potassium azide from the soil.

Soil surface applications of crabgrass (Digitaria spp.) herbicides prevented rooting of Bermudagrass (Cynodon dactylon L., var. 328) from the stolon nodes. Inhibition of root development was confined to the areas of the stolon which were in direct contact with dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA). Placement of the herbicides at various soil depths reduced the number of roots developing below the treatment; however, normal root growth occurred above the treated layer. Under field conditions, certain crabgrass herbicides delayed normal rooting of Bermudagrass from nodes for 12 weeks. Established root systems were not appreciably altered by the herbicidal treatments.

Subsurface application of liquid or granular formulations of ethyl N,N-dipropylthiocarbamate (EPTC) at planting time effectively controlled annual grass weed species in new seedings of alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.). Control of annual broadleaf weeds by EPTC was incomplete. A postemergence application of 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) in addition to the EPTC treatment resulted in excellent overall weed control. Benefits of weed control were more evident in birdsfoot trefoil than alfalfa.

Three facets of the phytotoxicity of disodium methanearsonate (DSMA) incorporated in soils were studied in seven greenhouse experiments. Growth of cotton planted immediately after incorporation of DSMA in Bosket silt loam was reduced significantly by herbicide concentrations of 50 to 80 ppmw. Toxicity appeared to decrease with time, particularly during the first 16 weeks after incorporation. DSMA incorporated in Bosket silt loam at 120 ppmw did not inhibit significantly the growth of cotton planted 32 weeks later. The addition of phosphorus to two silt loam soils increased the toxicity of DSMA to cotton. The incorporation of 50 ppmw of DSMA in Bosket silt loam inhibited rice growth by 75%, soybeans by 39%, oats by 12%, corn and cotton by 10%, and wheat by 0%. Rice growth was not affected in Dubbs silt loam or Sharkey clay by DSMA at concentrations as high as 100 ppmw.