Foliar applications of the dimethylamine salt of 4(2,4-dichlorophenoxy)butyric acid (2,4-DB) were effective for controlling cocklebur in soybeans. Treatments usually caused crop injury, but treated soybeans often produced higher seed yields than untreated soybeans heavily infested with cocklebur plants. Soybean injury was associated with the mechanical shielding of soybeans by the cocklebur infestation and soil moisture stress at time of treatment. Droughty conditions prior to treatment intensified crop injury and reduced soybeans yields.

Applications of disodium methanearsonate (DSMA) killed Johnsongrass foliage in field and greenhouse experiments. Control of regrowth following treatment increased with increasing rates, but there was no indication of translocation to rhizomes. DSMA toxicity did not change in 20 to 80 gpa water, but somewhat less control was obtained in 10 gpa. Addition of a surfactant to spray solutions increased toxicity. Control was not affected by stage of Johnsongrass growth, but observations indicated increased control during droughty conditions. Repeated usage provided seasonal Johnsongrass control equal to that obtained with sodium 2,2-dichloropropionate (dalapon), although more frequent applications were necessary.

Dimethyl sulfoxide, soil-incorporated at rates of 20 to 240 gpa, prevented the growth of roots and delayed and inhibited the growth of shoots of plants developing from purple nutsedge (Cyperus rotundus L.) tubers for a period of about two months. This effect upon growth occurred only while the tubers and developing plants remained in treated soil; transplanted to untreated soil, subsequent growth of roots and shoots was immediate and normal. The effective soil-residual life of dimethyl sulfoxide was about three months, irrespective of dosage. Dosages of 2½ to 7½ gpa had no effect upon the growth of the nutsedge plants. At 10 and 15 gpa, the inhibitory effect of dimethyl sulfoxide becomes apparent.

Following root application of a selective rate of 3-amino-2,5-dichlorobenzoic acid-C14 (amiben-C14), the translocation of radioactivity from roots to shoots was greater in pigweed (Amaranthus retroflexus L.), a susceptible plant, than in soybeans, a resistant one. Most of the radioactivity extracted from soybean and pigweed plants was present as conjugates of amiben-C14. The conjugate extracted from soybean was chromatographically identical with an N-glycoside prepared from glucose and amiben. In soybean plants, 3-amino-2,5-dichlorobenzoic acid also was converted to N-glycosylamiben.

Germination of wild carrot (Daucus carota L.) was not confined to any season but was correlated with abundant soil moisture in field studies. In laboratory studies, germination percentage for any seed lot increased with time as dormancy was overcome. Further, the germination was not clearly correlated with seed weight, light, or pH, but temperature and the availability of water were clearly significant. Dormancy was due to the endosperm which surrounds the embryo. When part of the endosperm covering the tip of the radicle was digested or broken off, germination was increased nearly to the potential for a given lot of seed

Non-lethal dosages of 2,4-dichlorophenoxyacetic acid (2,4-D), which stunted pigweed plants, markedly reduced transpiration. Lethal dosages of 2,4-D, 2,2-dichloropropionic acid (dalapon), or toxic oil reduced transpiration rapidly, but transpiration continued until treated plants were air dry. Large plants died slower than small plants after herbicide treatment; consequently, they transpired more water before death.

The response of four growth stages of Setaria glauca (L.) Beauv. (yellow foxtail), Eleusine indica (L.) Gaertn. (goosegrass), and Dactyloctenium aegyptium (L.) Richt (crowfootgrass) to dimethylarsinic acid (cacodylic acid) applied at rates of 0.25, 0.5, and 1.0 lb/A was studied.

The four growth stages for chemical treatments were generally: (a) early tillering, (b) late tillering, (c) boot, and (d) post-heading. Seed production was reduced by as much as 96% in yellow foxtail, 80% in goosegrass, and 37% in crowfootgrass. Application of the chemical at the “boot” stage was most effective although earlier applications also were effective. Inflorescences often were malformed. Other growth effects suggested a growth regulator type activity.

Detoxication of 3,6-dichloro-o-anisic acid (dicamba) in incubated soils was greater in heavier soil types and soils with higher moisture contents and higher temperatures. Dicamba phytotoxicity was less at 21 C than at 27 or 32 C. Over a pH range of 4.1 to 9.4, dicamba had a net negative charge. Dicamba showed considerable adsorption onto a kaolinite clay but little adsorption onto other clays and soils studied. Dicamba-1-C14 mixed with autoclaved Sharpsburg silty clay loam soil and incubated at 0, 33, 75, and 100% relative humidity and 35 C sustained very little volatilization loss over an 8-week period. However, nearly one-half of the radioactivity of dicamba-1-C14 on bare planchets at 0 and 100% relative humidity and 35 C was lost during an 11-week incubation period.

Glasshouse and field experiments were conducted on fine sandy loam, sandy clay loam, and clay to study under high temperatures 2-chloroallyl diethyldithiocarbamate (CDEC) and ethyl N,N-dipropylthiolcarbamate (EPTC) incorporated with the surface ½, 1, 2, and 3 in of soil and unincorporated. Herbicides, sprayed on the soil surface, were incorporated either manually in the glasshouse or with a powered, rotary tiller in the field. The principal weed species were Palmer amaranth (Amaranthus palmeri S. Wats.), redroot pigweed (Amaranthus retroflexus L.), junglerice (Echinochloa colonum (L.) Link), and barnyardgrass (Echinochloa crusgalli (L.) Beauv.). Performances of herbicides were determined by counting the plants 2 weeks after treatment.

The herbicidal performance of CDEC was greater when the applications were incorporated with the surface ½ or 1 in whereas the performance of EPTC increased with increasing depths of incorporation up to 3 in. Soil temperature, soil moisture losses, and the distribution of herbicide in soil apparently contributed to differential herbicide performance.

The loss of 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) and 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon) from an aquatic situation was studied. Appreciable loss of herbicides did not occur until 8 and 16 weeks after application of neburon and monuron, respectively. Periods of loss at an accelerated rate followed until approximately 50% of the herbicides disappeared. Further loss was observed but at a steadily decreasing rate. Approximately 15% of the monuron and 39% of the neburon remained after 128 weeks. More monuron was found in water than in soil during the first 32 weeks. After 32 weeks, most of the monuron was found in the soil and was largely in the top 4 in. The largest fraction of neburon was recovered from the soil and soil surface during all 128 weeks. Monuron moved down in the soil more readily than neburon.

Among 12 of the more effective surfactants selected from a preliminary experiment, there were few differences in their ability to increase atrazine toxicity to large crabgrass [Digitaria sanguinalis (L.) Scop.] and sorghum (Sorghum vulgare Pers.), or in toxicity to large crabgrass and sorghum when used alone. Surfactants per se showed some toxicity to large crabgrass and sorghum. As large crabgrass increased in size, it became less susceptible to injury from atrazine plus dodecyl ether of polyethylene glycol (Surfactant WK). Early spraying with atrazine plus Surfactant WK reduced the top-growth yield of six grass species.

In field studies, atrazine alone and surfactants plus atrazine applied at the 1-in weed height gave very good early weed control. Field plots treated at the 4-in weed height generally produced more weed top-growth and less sorghum than plots treated at the 1-in height. Only the preemergence atrazine treatments gave weed yields that were equal to treatments that included handweeding. Sorghum injury from the surfactants was evidenced by reduced stover yields.

Atrazine plus surfactant toxicity to emerged large crabgrass, grown in growth chambers, increased with higher relative humidities. This was not true for sorghum. The 1% surfactant mixtures generally had a lower surface tension than the 0.1% concentrations although the differences were not great. Surface tension was not the main factor governing the phytotoxicity of foliar-applied atrazine solutions. Translocation of atrazine from sorghum and large crabgrass leaves dipped in a C14-ring-labeled atrazine solution was very slight or nonexistent.

The tolerances of wheat and wild buckwheat (Polygonum convolvulus) to various rates of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) were determined under field conditions and supplemented by studies with wheat in the growth chamber. Wheat height and yield were inversely proportional to rate, but response to various rates was dependent on stage of growth at application. Greatest reductions in wheat height and yield resulted from treatment at the late tiller and boot stages, respectively. The weight per 100 wheat seeds was increased from treatment at the boot and flower stages but was decreased at the early tiller stage.

The ratio of peduncle length: length of the flag leaf-sheath was decreased most from 24 oz/A applied preemergence and 12 oz/A applied at the late tiller stage.

Growth rate of wheat was decreased for a 2-week period after treatment. Excellent kill of wild buckwheat was observed from all rates applied through the 12- to 15-leaf stage of growth.

Plots infested with quackgrass (Agropyron repens (L.) Beauv.) were treated with 2-chloro-4-ethylamino-6-isopropyl-s-triazine (atrazine) at several rates at various times and subjected to a number of cultural and cropping treatments. Depletion of carbohydrate reserves in the rhizomes increased with time after treatment. Recovery of the quackgrass occurred after 2 lb/A but usually not after 4 lb/A applications. Applications of nitrogen increased the rate of carbohydrate depletion. Two applications of atrazine at reduced rates were equal or superior to a single heavy rate. Tillage after treatment and crop competition improved the control of quackgrass obtained.

The adsorption and desorption of 2-chloro-4-ethylamino-6-isopropyl-amino-s-triazine (atrazine) as affected by pH, temperature, and cencentration of atrazine were studied on Drummer clay loam soil and a humic acid isolated from Leonardite. The adsorption of atrazine on the soil increased as pH decreased, but it was affected only slightly by temperature and cencentration of atrazine. Desorption of atrazine was greater with increasing temperature and pH. The adsorption of atrazine on the soil was reversible and desorption was nearly complete. Adsorption of atrazine on the humic acid increased as pH decreased and temperature increased, and there was very little desorption of atrazine from the humic acid.

The effect of ultraviolet (UV) light (240–260 mμ range) on 6, 7-dihydrodipyrido (1, 2-a:2’,1′-c)-pyrazidiinium salt (diquat) and 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat) was studied. Both dipyridyls were very stable in dark but were altered rapidly in the presence of UV light. Radioassay data collected from planchets containing solidified diquat or paraquat indicated a loss of more than 50% of the C14 from both compounds after 48 hr and more than 75% after 96 hr. When radioactive aqueous solutions were placed under UV lights, little change in the radioactivity occurred during an 8-day period as determined by liquid scintillation. When the concentration of diquat or paraquat in these solutions was determined by chemical analysis, degradation of the original molecules was observed.

Information obtained by autoradiography of chromatograms, spotted with radioactive aqueous solutions exposed to UV light, indicated that two or possibly more C14-containing degradation products were formed from both diquat and paraquat. Co-chromatography indicated that one degradation product from paraquat was 1-methyl-4-carboxy-pyridinium ion.

New Line Early Perfection peas (Pisum sativum L.) in the 10th-node stage were treated with a foliar broadcast application of 1 lb/A of the sodium salt of carboxyl carbon-14 labeled 4-(2-methyl-4-chlorophenoxy) butyric acid (MCPB*). Direct counting of C14 indicated that MCPB* equivalent to 8.4 ppm on the fresh weight basis was in or on the pea tissue immediately after treatment. The concentration declined rapidly for 6 days following treatment and then at a reduced rate until shelled pea harvest 5 weeks later. Translocation of C14 was studied by autoradiography. Most of the labeled material was retained at the application site. Very little was translocated to the new growth or into the pea seed. The plants retained C14 equivalent to 0.4 ppm MCPB* at the time of harvest with a concentration in the shelled peas of not more than 0.1 ppm.

Surface applications of 4-amino-3,5,6-trichloropicolinic acid (picloram) were made at 5 rates on 3 soil types. The picloram-treated areas were sampled 3 times after herbicidal application to determine the extent and movement of herbicide residues. The region of highest picloram concentration in a heavy- and medium-textured soil, when sampled 9 and 15 months after application, was near the surface. On the light-textured soil, picloram moved more completely through the surface 2 ft of soil with greatest herbicide concentrations generally found at the deepest sampling depth. Applications of picloram were dissipated faster at low rather than at high rates on all 3 soil types. Concentrations of phytotoxic residues at the end of the study period were greatest in the heavy-textured soil with the highest organic content.

Two-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 5-bromo-3-sec-butyl-6-methyluracil (bromacil), and 6,7-dihydrodipyrido-(1,2-a:2’,1′-c)-pyrazidiinium salt (diquat) significantly inhibited photosynthetic C14O2-fixation to varying degrees in corn (Zea mays L., var. Dixie 18), cotton (Gossypium hirsutum L., var. Deltapine), and soybeans (Glycine max (L.) Merr., var. Lee). Atrazine treatments of 10 ppm overloaded the protective mechanisms in corn and cotton. Both 1 and 10 ppm of atrazine reduced C14O2-fixation to less than 5% of controls in soybeans, a sensitive species. One ppm of bromacil and of diquat reduced C14O2-fixation in all three crops, but diquat was less inhibitory than either bromacil or atrazine. Except for diquat on corn, herbicides had no significant effect on C14O2-fixation in the dark. Treatments in which photosynthetic C14O2-fixation was 5% or more of controls had little effect on the kinds or relative amounts of C14-labeled compounds produced. Only the total amount fixed was reduced. Treatments, in which photosynthetic C14O2-fixation was less than 5% of controls, caused a significant reduction in the relative amounts of sucrose and alanine produced; however, the relative amounts of malic, aspartic, and glutamic acids increased.

In the greenhouse, 20% granular isopropyl N-(3-chlorophenyl) carbamate (CIPC) at 6 lb/A provided 100% dodder control for 3 to 6 weeks. In the field, 95 to 100% control persisted beyond the expected soil life of CIPC because shade from the crop plants inhibited dodder development and dry soil reduced dodder germination. Effective control required uniform distribution on the soil before the dodder was wrapped on the host plant. CIPC was most effective when applied on the soil surface; incorporation ½, 1½, or 3 in deep reduced its effectiveness. It controlled dodder well if applied to moist soil but was less effective when the soil surface was dry. Partial shade from the crop at the time of application increased the effectiveness of CIPC. Under certain undefined conditions, CIPC applied to the soil injured attached dodder. However, it was consistently effective only on dodder seedlings before attachment.

A study was made with glucose-1-C14, glucose-6-C14, and glucose U-C14 to determine quantitatively the effects of 2,2-dichloropropionic acid (dalapon) on glucose utilization in roots and shoots of one-week-old barley seedlings. An attempt also was made to determine the major pathway of glucose metabolism involved. Dalapon apparently did not change the normal pathway of glucose metabolism but interferred with glucose utilization as evidenced by differences in radioactivity of sugars and organic acids. Partial blocks may be operative initially at the beginning of the glycolytic pathway and subsequently in the Krebs cycle.