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.

Concentrations of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) causing 50% growth reduction (hereinafter referred to as GR50) were determined in nutrient culture and 64 simulated soils using foxtail millet (Setaria italica (L.) Beau.) as an indicator species. The relative order of effectiveness of soil components in reducing trifluralin phytotoxicity was steamed organic matter ≫ organic matter ≫ steamed montomorillonite ≥ steamed kaolinite ≃ kaolinite ≃ montmorillonite. Steaming the organic matter more than doubled the anion exchange capacity. Anion exchange capacity was a better parameter than cation exchange capacity for assessing the potential of an adsorbent to reduce phytotoxicity. Surface area, cation exchange capacity, and adsorption of trifluralin from solution were less reliable indices. The effectiveness of organic matter in reducing phytotoxicity may be due to the exchange capacity and high surface area. Montomorillonite apparently interacted synergistically with other adsorbents to reduce phytotoxicity. Trifluralin did not adsorb on the internal surfaces of montmorillonite as judged by surface area comparisons and X-ray diffraction determinations. Increasing moisture content appeared to block the active sites of trifluralin adsorption. This may be concluded from greater vapor movement and decreased adsorption from a xylene solvent system for moist compared to air dry soils.

Bean plants (Phaseolus vulgaris L. var. Black Valentine) pretreated with gibberellic acid (hereinafter referred to as GA) absorb and accumulate considerably more N-1-naphthylphthalamic acid (naptalam) than untreated plants. All concentrations of GA from 2.9 × 10−6 to 8.6 × 10−4M were effective; peak influence occurred at 6 × 10−4M. Plants pretreated with this concentration took up 58% more naptalam than untreated plants. When the different parts of the plant were analyzed for naptalam separately, the leaf area (on a per g dry weight basis) was influenced most by GA pretreatment. The leaf area of bean plants pretreated with 2.9 × 10−4M contained 212% more naptalam than the leaf area of untreated plants. The leaf area also included all stem and petiole tissue above and including the first true leaves.

An extensive search of the literature and records was conducted to determine when and how johnsongrass (Sorghum halepense (L.) Pers.) was introduced into the United States. Previous authors surmised that johnsongrass was imported from the Mediterranean area, but my search revealed that no agriculturist from the United States had worked in the Mediterranean region before 1840. Although Dr. James B. Davis assisted the Turkish Empire in cotton culture in the 1840's, there is evidence that johnsongrass was grown throughout the Southeast by 1830 if not before. Documentation of the initial introduction and distribution was hampered by the use of more than 40 common names for this weed in the nineteenth century. At least eight different Latin names were used to identify johnsongrass in the 1800's. The use of johnsongrass as a common name on a national basis resulted from a letter written by Herbert Post of Selma, Alabama, in 1874 to George Vasey, an employee of the U. S. Department of Agriculture in Washington. In 1880, John Haralson of Selma, Alabama, wrote to D. L. Phares of Woodville, Mississippi, that johnsongrass was the common name used in his area. These letters were published in the Monthly Report of the U. S. Department of Agriculture and in Farmers Book of Grasses, respectively; the wide attention that these received resulted in the common name of johnsongrass. The name was derived from that of William Johnson, a farmer of Marion Junction, Alabama, who presumably introduced it into Alabama. By the late nineteenth century, the presence of johnsongrass was almost nationwide. Many reports testify to the severity of the problem caused by this weed in the late 1800's. Its pernicious nature led to the first Federal appropriation specifically for weed control in 1900, and to the first report on johnsongrass control, prepared by C. R. Ball in 1902.

Detached live oak (Quercus virginiana Mill.) leaves were immersed in aqueous solutions of 4-amino-3,5,6-trichloropicolinic acid (picloram) or (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) for periods up to 4 hr. Herbicide concentration ranged from 10−3 to 10−6M; solutions were adjusted to either pH 4, 6, 7, or 8. Absorption of picloram in the presence of equimolar concentrations of 2,4,5-T exceeded that noted for picloram alone. The presence of picloram in the treating solutions had no effect on absorption of 2,4,5-T. This technique allows evaluation of absorption and penetration characteristics of mixtures of herbicides, solvents, and adjuvants.

The plant characteristics which makes ‘Hybelle’ cabbage (Brassica oleracea var. capitata L.) relatively tolerant while ‘Rio Verde’ is susceptible to the toxic action of 2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen) were investigated. No differences between ‘Hybelle’ and ‘Rio Verde’ were found in growth rates, light or dark germination, or stomata density. Little xylem or phloem translocation of nitrofen-14C occurred. Disruption and removal of the cuticle of ‘Hybelle’ increased its susceptibility to nitrofen while ‘Rio Verde’ with more than normal wax deposition was tolerant. Plants with less cuticle were more susceptible, regardless of cultivar. ‘Hybelle’ had more wax per unit surface than ‘Rio Verde’ and wax deposition increased with leaf age. Both cultivars were equally tolerant to nitrofen when 6 weeks old. ‘Rio Verde’ leaves absorbed nitrofen-14C twice as fast as ‘Hybelle’ leaves. The results show that the mechanism of intraspecific selectivity of cabbage to nitrofen is dependent on the amount of cuticular wax on the leaves at the time of nitrofen application.

The metabolism of 3′,4′-dichloropropionanilide (propanil) to 3,4-dichloroaniline (hereinafter referred to as 3,4-DCA) and N-(3,4-dichlorophenyl)glucosylamine (hereinafter referred to as 3,4-DCAG) was quantitatively modified in rice (Oryza sativa L. ‘Nato’) by temperature and day length. The propanil, 3,4-DCA, and 3,4-DCAG content of rice was determined 1, 2, 5, and 8 days after root treatment with 92 μM propanil. Plants were grown and treated under long-day (16 hr) and short-day (12 hr) conditions with day temperatures of 32, 27, or 21 C and night temperatures of 21 C. Absorption and metabolism of propanil were most rapid under high temperature and long day conditions. A mean value of 0.75 μmoles total of aniline equivalent per plant was obtained. Greater quantities of 3,4-DCA and 3,4-DCAG were recovered from plants in high temperature, long day environments. An average of 47% of the propanil plus water-soluble metabolites in rice was in root tissue. Conditions favoring high growth rates and transpiration increased the percentage in the shoots. Because of the increased tissue mass at high temperatures, mean concentrations of propanil plus water-soluble metabolites in plant tissue were reduced from 0.18 to 0.12 μmoles/g dry weight.

Eight herbicide postemergence treatments were applied to proso millet (Panicum milaceum L.) at three growth stages. The dimethylamine salt of (2,4-dichlorophenoxy)acetic acid (2,4-D) at 0.56 kg/ha had significantly higher grain yields than the weedy check. All herbicides except the amine of 2,4-D at 0.28 kg/ha appeared to injure proso millet plants by varying degrees; however, yields were not greatly affected. All herbicides gave excellent control of redroot pigweed (Amaranthus retroflexus L.) when applied to proso millet in the 4 to 6-leaf stage. Weed control was poorer when spraying was delayed until proso millet was in pre-boot and post-flower stages.

The phenolic content of purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (Cyperus esculentus L.) was determined. The major phenolic components were p-coumaric, ferulic, p-hydroxybenzoic, syringic, vanillic, salicylic, proto-catechuic, and caffeic acids, and eugenol. High concentrations of eugenol and salicylic acid inhibited the sprouting of nutsedge tubers. The lack of activity at lower concentrations argues against a major role for these compounds in maintaining nutsedge tuber dormancy. Exogenous abscisic acid inhibited nutsedge tuber sprouting and may be a natural dormancy factor in nutsedge.

The activity of foliage applications of N,N-dimethyl-2,2-diphenylacetamide (diphenamid) was greatly enhanced by exposing the plants to high relative humidity for 6 hr immediately after chemical application. Growing plants under low light intensity further increased the activity of diphenamid under these conditions. This response occurred with a number of plant species, including tomato (Lycopersicon esculentum Mill.), Japanese millet (Echinochloa crusgalli (L.) Beauv., var. frumentacea), lettuce (Lactuca sativa L.), and radish (Raphanus sativus L.). Low light, but not high relative humidity, increased the activity of diphenamid as a soil application. Unaltered diphenamid and not its known metabolites seemed to be responsible for the increased activity of foliage sprays under conditions of low light and high relative humidity.

Young vegetative clones of yellow nutsedge (Cyperus esculentus L.) were propagated by subdivision of older clones and then grown 6 months under photoperiods of 8 to 24 hr. Early stages of development of basal bulbs, tubers, and flowering structures were characterized in terms of apical meristem activity and differentiation of various foliar appendages: cladophylls, prophylls, leaf primordia, foliar tube development, and involucral leaves. Ramification of the axial stem system was interpreted as a repeating phylogenetic sequence: viz., undifferentiated axial meristem (from basal bulb) å primitive stem (rhizome) å advanced stem (new basal bulb). New photosynthetic leaves differentiated every 4.5 to 5 days, and each exhibited a sigmoid pattern of growth for 24 to 40 days. As photoperiods increased from 14 to 24 hr, certain active vegetative processes—total peripheral shoot development, rhizome proliferation, and rate of higher order shooting—were progressively promoted. The rate of differentiation of indeterminate rhizome tips into basal bulbs (new shoots) was maximum at 16 hr and into tubers at 8 to 12 hr. Delayed tuberization, however, occurred even at the longest photoperiod. Flowering occurred only at photoperiods of 12 and 14 hr. Active vegetative processes were competitive with tuberization, and flowering was competitive with both active and dormant vegetative development.

Gas chromatographic analysis of benzene extracts was used to study the effects of temperature and relative humidity on the degradation and volatilization of 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) in the soil. The relative humidity of a closed system had little effect on alachlor retention in air dry Sawyer fine sandy loam at 22 C, but had a pronounced effect when soil temperature was 38 C or higher. At 0% relative humidity (38 C or 46 C) alachlor was degraded to 2-chloro-2′,6′-diethylacetanilide. Decomposition, which also occurred in 5 N aqueous HCl, was attributed to acidic soil water film surfaces. As relative humidity within the system increased, the rate of degradation decreased, apparently because condensation of water vapor increased the thickness of the soil water film and decreased the surface acidity. At 38 C, minimum loss was noted at 31% relative humidity, and at 46 C, minimum loss was found at 79% relative humidity. The increased loss of alachlor at relative humidities above these critical points was attributed to volatility and not to chemical degradation.

Wild buckwheat (Polygonum convolvulus L.), leafy spurge (Euphorbia esula L.), yellow foxtail [Setaria glauca (L.) Beauv.], and wild oat (Avena fatua L.) hydroxylated, in a 7-day period, 2 to 7% of the (2,4-dichlorophenoxy)acetic acid-1-14C (2,4-D-1-14C) absorbed. Only a trace of hydroxylation products was detected in wild mustard [Brassica kaber (DC.) L. C. Wheeler var. pinnatifida (Stokes) L. C. Wheeler], perennial sowthistle (Sonchus arvensis L.), and kochia [Kochia scoparia (L.) Roth]. The investigation was limited to hydroxylation on the para-position of the herbicide. The predominant product, 2,5-dichloro-4-hydroxyphenoxyacetic acid, was detected in all weed species studied. Also found in measurable amounts in some species were 2,3-dichloro-4-hydroxyphenoxyacetic acid and 2-chloro-4-hydroxyphenoxyacetic acid. The hydroxylation rate on the number four carbon of the ring did not account for the variation in susceptibility exhibited by these plants.

Studies were conducted on the growth and development of 55 morphologically distinct vegetative types of johnsongrass (Sorghum halepense (L.) Pers.) collected throughout the United States and from several foreign countries. Observations were made also on the growth of sorghum almum (Sorghum almum Parodi) from three foreign countries. Mature leaf-blades of the different johnsongrass ecotypes varied in length from 31 to 59 cm and in width from 1.7 to 3.4 cm. Plant height and culm density varied 2 to 4-fold for the different ecotypes. Floret production varied from 87 to 352 sessile spikelets for representative panicles of the different ecotypes. The number and arrangement of branchlets within panicles also varied as did the size of various spikelet components. Sorghum almum produced much taller plants than did johnsongrass although culm density and lateral growth were less than that of johnsongrass.

Sericea lespedeza (Lespedeza cuneata (Dumont) G. Don, var. Serala) was planted in three field experiments at three seeding rates with four rates of S-propyl dipropylthiocarbamate (vernolate). Grass and broadleaf weed populations were reduced, but sericea was unaffected by vernolate incorporated preplant. Use of a herbicide permitted a reduction in seeding rate with no decrease in sericea stand or forage yield. This treatment permitted harvesting a cutting of hay the establishment year with only a minor effect on production the next year. The beneficial effect of vernolate on sericea yield continued the second year, mainly because sericea plants were better established and more vigorous. Sericea seeding rate did not affect weed competition or forage yield. A seeding rate of 11 kg/ha with 3.4 kg/ha vernolate was the most practical treatment.

A 3-year field experiment was initiated in 1967 to study the effects of herbicides in combination with the systemic insecticide, O,O-diethyl S-2-[(ethylthio)ethyl] phosphorodithioate (disulfoton) on cotton (Gossypium hirsutum L.). Herbicide treatments of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 1,1-dimethyl-3-(α,α,α,-trifluoro-m-tolyl)urea (fluometuron), 3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea (norea), 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin), and α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) did not significantly affect yield of weed-free cotton while disulfoton treatment significantly increased yield over the 3-year period. Yield with disulfoton was negatively correlated with number of thrips (Thripidae sp.). No interaction occurred between herbicides and disulfoton on yield, and only in 1 year was there an effect on stand.

Foliar-spray and radioisotope herbicidal studies were conducted near Tucson, Arizona, to study factors influencing absorption, translocation and toxicity of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in creosotebush [Larrea tridentata (DC.)Cov.]. Maximum absorption and translocation of 14C-labeled 2,4,5-T occurred approximately 30 days after initiation of effective summer rains and coincided with maximum total killing of creosotebush. This occurred during the full-flowering to mid-fruiting stage of phenological development, overlapped the period of old leaf drop, and was due in part to the generally greater basipetal translocation of radioactive 2,4,5-T from old leaves, flowers, fruits, and young bark than from young leaves. Translocation of radioactive 2,4,5-T was relatively slow, 1 to 5 cm per hour, and basipetal movement ceased after 18 to 24 hr, following which the 2,4,5-T largely disappeared from the vascular tissues of the stem. Absorption of 2,4,5-T by the leaves was low during dormancy and may have limited herbicidal effects during this period, but it was not a factor during the season of high susceptibility.

Winter wheat (Triticum aestivum L., var. Gaines) plots infested with seedling blue mustard (Chorispora tenella (Willd.) DC) were hand-weeded or treated in the fall with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) at 1 lb/A and 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) at ⅜ lb/A. Additional wheat plots were established in the fall with populations of one, three, and nine blue mustard seedlings per square foot, and the next spring these were either untreated, hand-weeded, or treated with (2,4-dichlorophenoxy)acetic acid (2,4-D) at 1 lb/A. All plots were harvested in July. Maximum wheat yields were obtained from plots hand-weeded or treated in the fall. Wheat production decreased significantly as weed population increased. Grain yield reduction, resulting from weed competition during the winter months, was significant and accounted for more than 50% of the total loss.

Effects of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) rate and placement in soil on growth and anatomy of soybeans (Glycine max (L.) Merr.) were studied in greenhouses. In 7-week-old plants, trifluralin caused pronounced changes in number and organization of palisade cells in leaves. In fourth internodes, xylem elements of treated plants were less organized and walls of pericycle fibers were extremely thick compared to those of untreated plants. There was starch accumulation in nodules and in xylem elements of the upper root, and binucleate and trinucleate cells were present in tips of tap and lateral roots of treated plants. The effects were more pronounced as rate of trifluralin was increased from 0.36 to 0.74 and to 1.1 kg/ha and when trifluralin was incorporated into the 5 to 15-cm depth rather than the top 5 cm of soil. However, occlusions of xylem vessels in lateral and tap roots were most pronounced at 0.74 kg/ha. Plant topgrowth was reduced more when trifluralin was incorporated into the bottom 10 cm of soil, but root growth inhibition was not affected by trifluralin placement. Trifluralin reduced nodulation of soybeans and seemed to inhibit utilization of cotyledonary reserves and redistribution of organic and mineral constituents of unifoliolate leaves.

Postemergence treatments with 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea [chloroxuron], for broadleaf weed control in soybeans [Glycine max (L.) Merr.] often partially defoliate, and temporarily stunt the crop. Chloroxuron was applied at 3 lb/A and at 1, 1½, and 3 lb/A with surfactant over the tops of weed-free soybeans in the cotyledon, unifoliate, and first trifoliolate stages of growth in 1967, 1968, and 1969. Relatively small but statistically significant yield reductions, particularly from treatments in the unifoliate stage, resulted in 1967. No significant yield reductions resulted in 1968 or 1969. These studies demonstrated the ability of soybeans to withstand initial injury from early postemergence treatments with chloroxuron without serious reductions in yield.