Studies were conducted to determine the effect of simulated rainfall on the phytotoxicity of several herbicides. Oil soluble herbicides 4,6-dinitro-o-sec-butylphenol (DNBP), pentachlorophenol (PCP), a 1:1 mixture of the butyl esters of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid (2,4-D: 2,4,5-T), and a 2:2:1 mixture of the isooctyl esters of 2,4–13:2,4,5-T: 4-amino-3,5,6-trichloropicolinic acid (picloram) (hereinafter referred to as M-3140), usually were less affected by artificial rainfall than were water soluble 1,1'-dimethyl-4,4'-bipyridinium salt (paraquat), dimethylarsinic acid (cacodylic acid), and cis-2,3,5,5,5-pentachloro-4-ketopentenoic acid (hereinafter referred to as AP-20), on guava (Psidium guajava L.) and mango (Mangifera indica L.). Washing reduced the activity of some oil and water-soluble herbicides on sorghum (Sorghum bicolor (L.) Moench, var. Combine Kafir-60) and dioscorea (Dioscorea composita Hemsl). As herbicide rates were increased, washing reduced the phytotoxicity of paraquat and 2,4-D:2,4,5-T less on mango and guava. Artificial rainfall applied as a mist spray at different intervals had no effect on the phytotoxicity of paraquat; it reduced the activity of cacodylic acid and increased the effectiveness of AP-20 on mango.

Radioautographs showed that root uptake of 14C-methanearsonic acid (MAA-14C) by johnsongrass (Sorghum halepense (L.) Pers.) from nutrient solution was rapid and translocation into all portions of the plant occurred within 4 hr after treatment. Basipetal and acropetal translocation of foliar and stem-applied MAA-14C occurred in both johnsongrass and cotton (Gossypium hirsutum L., var. Rex smooth leaf), indicating that movement of the herbicide probably occurs in both phloem and xylem tissue. However, acropetal movement of MAA in both plants occurred at a higher rate than basipetal movement, and basipetal movement in cotton was not as rapid as in johnsongrass. Methanol extracts of MAA-14C johnsongrass were chromatographed. Radioactive spots with Rf values different from the MAA-14C standard were observed. Use of location reagents on the chromatographs suggested that MAA-14C may complex with either a sugar or organic acid or both. Amino acid fractions were prepared from methanol extracts of both plants. An MAA metabolite, with a positive reaction to ninhydrin, was located on chromatographs spotted with the amino acid fraction from johnsongrass but was not present in the cotton fraction. A comparison of Rf values suggests that the metabolite may be a combination of the MAA molecule with histidine or one of its analogues. Spectrophotometric determination showed a build-up of amino acids in MAA-treated johnsongrass but not in cotton. The increased levels of amino acids in johnsongrass suggest that the MAA metabolite may be blocking a protein synthesis pathway, or some other unknown biosynthetic pathway.

Isopropyl m-chlorocarbanilate (chlorpropham) at 6 lb/A, the standard treatment, usually controlled dodder (Cuscuta spp.) completely for 3 to 5 weeks. Of 27 other herbicides compared with chlorpropham, seven controlled dodder completely for longer periods (6 to 18 weeks), and nine for comparable or slightly shorter periods. Eleven controlled dodder only partially or completely for a period shorter than that from chlorpropham. The period of dodder control from chlorpropham was doubled when p-chlorophenyl N-methylcarbamate at 1.5 lb/A was included with it.

We investigated the periodicity of germination, longevity of caryopses viability, and reproductive capacity of downy brome (Bromus tectorum L.) populations in relation to chemical and mechanical fallow and fall tillage weed control treatments. The important factors in the dynamics of downy brome populations are: (a) large numbers of viable caryopses are carried from 1 year to the next in the litter and soil; (b) downy brome caryopsis production is density dependent; and (c) the simultaneous germination characteristics of freshly harvested downy brome caryopses can be conditioned environmentally to continuous germination.

Land was prepared conventionally in early spring for the planting of small seeded legumes. Planting was delayed to allow emergence of weeds. We applied 1,1'-dimethyl-4,4'-bipyridinium salts (paraquat) and planted legumes immediately afterwards. Stage of weed growth, time of herbicide application, rate of chemical applied, and the methods of seeding were variables imposed. Paraquat (plus surfactant) applied at 1.1 and 2.2 kg/ha to emerged weeds prior to the seeding of legumes controlled quackgrass [Agropyron repens (L.) Beauv.] sufficiently to allow excellent establishment of alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.). A paraquat application delayed until yellow nutsedge (Cyperus esculentus L.) was at least 10 cm in height, followed by a disking, controlled the sedge sufficiently to allow legume establishment. For annual weed control, 0.3% kg/ha of paraquat was sufficient. Drilling as a method of seeding gave better legume stands than did surface-seeding techniques.

Pond studies were conducted at Tishomingo, Oklahoma with wettable powder 2,6-dichlorobenzonitrile (dichlobenil) and at Denver, Colorado with granular dichlobenil to measure chronic effects on fish and other effects on the ecosystem. Decline of the herbicide was rapid at Tishomingo, with only about 3% of the material remaining after 11 days, while at Denver the herbicide took 3 weeks to reach peak concentration in the water and was still measurable in the water after 189 days. Dichlobenil was present in bottom sediments after 312 days at Tishomingo and after 166 days at Denver. Weeds were controlled at both locations, but regrowth occurred after 3 months in ponds treated at 10 and 20 ppm dichlobenil. No immediate mortality was sustained by fish at either locality, but day-to-day mortality was serious at higher concentrations at Tishomingo. Reproduction apparently was affected by higher dichlobenil levels at Tishomingo. Growth of fish was fastest in ponds treated with highest rates of dichlobenil at Tishomingo, and slowest in the untreated ponds. Residues of dichlobenil developed in fish from all ponds, but faster at Tishomingo than at Denver, and larger in high-treatment ponds than in low-treatment ponds. Some pathology was seen in liver, kidney, and pancreas of Tishomingo fish.

Turions of Hydrilla verticillata (Casp.) were treated with gibberellic acid (GA), napthaleneacetic acid (NAA), indoleacetic acid (1AA), 2-chloroethane phosphonic acid, 6,7-dihydrodipyrido(1,2,-a:2′, 1′-c)-pyrazinediium salts (diquat), 1,1′dimethyl-4,4′-bipyridinium salts (paraquat), mono-N,N-dimethylcocoamine salt of 7-oxabicyclo (2.2.1)heptane-2,3-dicarboxylic acid (cocoamine salt of endothall), or the dimethyl amine formulation of 2,4-dichlorophenoxyacetic acid (2,4-D). Germination and growth of subterranean turions was enhanced by GA and axillary turions by 1AA and 2,4-D. The herbicides exhibited little phytotoxicity to the propagules.

Twelve locations in the United States and Puerto Rico were the sites for determining the loss of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2,3,6-trichlorophenylacetic acid (fenac) from soil. The herbicides were contained in tubes (1.88 by 6 inches) placed at depths of 3, 9, and 15 inches in the field. The samples were placed horizontally to minimize losses due to vertical movement of water from the tubes. After at least 3 months in the soil, the samples were returned to Beltsville and analyzed. Average recoveries showed 61% more atrazine and 41% more fenac from the 15-inch depth than from the 3-inch depth. Five northern samples contained more than twice as much atrazine and fenac residue as four southern samples. A positive correlation existed between fenac retention and soil organic matter content. Increasing soil organic matter and depth of placement, and decreasing temperature, tended to make the herbicides more persistent. However, the data were quite variable and the variations were often unexplainable.

Seedlings of 22 plant species were evaluated in aqueous suspensions of N-(2-mercaptoethyl)benzenesulfonamide S-(O,O-diisopropyl phosphorodithioate) (bensulide), dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA), and 1-(2-methylcyclohexyl)-3-phenylurea (siduron) to determine their value as indicator plants for bioassays. The species showing the greatest sensitivity by reductions in root or shoot lengths were evaluated in soil mixtures to determine the level of sensitivity under soil conditions. These indicator plants, in most cases, proved reliable in detecting the presence and movement of bensulide, DCPA, and siduron in soils from field-treated plots. There appeared to be no accumulation in soil treated with four annual applications of bensulide, DCPA, or siduron.

Eighteen soil-active herbicides were evaluated for control of downy brome (Bromus tectorum L.) and associated broadleaf weeds during revegetation of big sagebrush (Artemisia tridentata Nutt.) rangelands in Nevada and in northeastern California. We rated all herbicides in reference to a chemical-fallow program for replacement of vegetation, where seeding follows and is separated from herbicide application by at least 1 year. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) applied at 1 lb/A was the most promising treatment with respect to three essential characteristics: length of activity, spectrum of weed control, and relative preemergence and postemergence phytotoxicity.

We modified a cereal huller to thresh seed of honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell]. The device threshes seed of other mesquite varieties, huisache [Acacia farnesiana (L.) Willd.], and other leguminous species.

Root applications of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at concentrations greater than 1.0 × 10-7M inhibited growth of parrotfeather (Myriophyllum brasiliense Camb.). Chromatographic analysis of exudate from detopped parrotfeather plants indicated that simazine was being tranlocated primarily as the intact molecule. A correlation coefficient of 0.985 was observed between the amount of simazine-14C removed from the treatment solution and transpiration during a 6-hr period. Absorption of simazine-14C by parrotfeather roots of intact plants was linear for the first 4 hr followed by a gradual decrease at the end of 6 hr. Simazine-14C at 1 and 2 hr after root applications was highest in the roots, intermediate in the lower part of the shoot, and lowest in the upper part of the shoot. After 192 hr, simazine-14C accumulated in the top of the shoot in a concentration higher than in the lower part of the shoot or the roots. A correlation coefficient of 0.988 was found between the amount of simazine-14C present in the tissue and the treatment concentration over a range of 1.2 × 10-6 to 5.0 × 10-6M.

Rates of photosynthesis, respiration, and transpiration of wheat (Triticum aestivum L., var. Gaines) were determined as functions of time, under controlled conditions of moderate soil water stress and soil temperature, after treatment of the roots with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). Air temperature, relative humidity, light intensity, and air movement were maintained constant. The rate of photosynthesis declined with time for all plants treated with diuron but not for the controls. No change in the rate of respiration was detected. The rate of transpiration decreased slightly immediately upon application of the diuron and then remained constant. The data indicate that soil temperature and soil water stress play important roles in the herbicidal action of diuron applied to the soil.

In laboratory studies with 3-amino-2,5-dichlorobenzoic acid (amiben), adsorption of 14C-amiben was less than 14C-amiben methyl ester with all adsorbents tested. Adsorption of 14C-amiben was closely associated with soil organic matter. Also, considerable adsorption of 14C-amiben and 14C-methyl ester was observed on illite clay and on Sassafras loamy sand which contains clay minerals composed primarily of illite clay. Root uptake of amiben caused more injury than shoot uptake to greenhouse-grown corn (Zea mays L., var. Nebraska 202). The relatively insoluble butoxy ethyl ester of amiben was the most toxic amiben derivative to greenhouse-grown corn. Subirrigation moved the more soluble amiben derivatives to the soil surface where they had less effect on the root system. In field studies comparing four derivatives of amiben applied preemergence to corn in 1966, best weed control was from the ammonium salt of amiben at 2 and 4 lb/A and the methyl and butoxy ethyl ester at 4 lb/A; the amide was ineffective. The ammonium salt of amiben caused early stunting of corn but did not reduce yield. Selective weed control in soybeans [Glycine max (L.) Merr., var. Clark] was obtained in 1966 with the ammonium salt, 80% wettable powder, and monomethyl amine salt of amiben at 1 1/2 lb/A, and the methyl and butoxy ethyl ester at 6 lb/A. In 1967, the best amiben derivatives for weed control in soybeans were the amide and esters. Amiben derivatives more susceptible to leaching were less effective in controlling weeds in 1967 due to excessive rainfall after amiben applications.

The effect of stage of growth of field bindweed (Convolvulus arvensis L.) on absorption and translocation of 14C-labeled 2,4-D and picloram was studied. Three stages of growth investigated were s-week old seedlings, and 7-week old and 16-week old vegetatively propagated plants. One middle leaf of each plant was treated with either 14C-labeled (2,4-dichlorophenoxy)-acetic acid (2,4-D) or 4-amino-3,5,6-trichloropicolinic acid (picloram). Treated plants were harvested after 48 hr and assayed for radioactive 14C. The percent of 2,4-D applied which was absorbed by seedlings was less than that absorbed by adult plants. Picloram absorption was not different in seedlings and 7-week old adult plants, but the 16-week old adult plants absorbed more picloram than either the 5-week old seedlings or 7-week old adult plants. More picloram than 2,4-D was absorbed at all stages of growth. Translocation of both 2,4-D and picloram was greater in seedlings than in older plants. No difference was found in amounts of 2,4-D and picloram translocated by adult field bindweed plants. More 2,4-D than picloram was translocated by seedlings.

Plots were planted to corn (Zea mays L., var. Mo. 880) and treated with 0, 2.5, 5.0, and 10 lb/A of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) or 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) in 1964 and in 1965. Soybean (Glycine max L., var. Clark 63) forage yields from soil samples collected in the spring, 1 year after application, were not affected by treatments of 5.0 lb/A or less of atrazine. Yields were reduced on soils collected in the fall (6 months) after application. Following 2 years of treatment, substantial reductions in yields of soybean forage occurred. Soybeans planted in the field following 2 consecutive years of herbicide treatment, yielded similarly to the control plots except when rates of 10 lb/A had been applied.

The influence of timing and method of application of sodium or disodium salts of methanearsonic acid (MAA) on cotton (Gossypium hirsutum L.) response, arsenic content of seed, and arsenic content of soils, was studied in field experiments in California, Arizona, and Mississippi. Methods of application consisted of directed and topical sprays. Directed sprays were applied to cover the small weeds in the drill row with a minimum of contact on cotton leaves more than 2 to 3 inches above the ground. Topical sprays were applied from nozzles positioned over the cotton in such a way that the entire cotton plant was subject to coverage. Rates of application were either 2 or 3 lb/A of the salts, and either two or three applications were made to treated plots. Cotton appeared highly tolerant to directed applications. A topical application to cotton 2 to 4 inches slightly reduced yields, but topical applications made at later stages of growth caused progressively severe reductions in yields and delayed maturity. The arsenic content of cottonseed from treated plots was not significantly higher than in that from untreated checks providing that applications were restricted to prebloom stages. Either directed or topical applications made during the blooming stage resulted in detectable increases of arsenic in the cottonseed. The effect of the treatments on arsenic content of soils was relatively small in comparison with natural levels, but the effect was detectable at one of the three locations.

Antagonistic responses were noted on sorghum (Sorghum vulgare pers.) and giant foxtail (Setaria faberii Herrm.) using preemergence combinations of (2,4-dichlorophenoxy)acetic acid (2,4-D) and the carbamates S-ethyl dipropylthiocarbamate (EPTC), isopropyl m-chlorocarbanilate (chlorpropham), and 2-chloroallyl diethyldithiocarbamate (CDEC). Combinations of EPTC and (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) or 3,6-dichloro-o-anisic acid (dicamba) gave similar results. Effects of these combinations were mainly additive on four dicotyledonous species. Combinations of 2,4-D and N-1-naphthylphthalamic acid (naptalam) also were antagonistic on sorghum and giant foxtail but were additive on the remaining species. Eight other herbicide combinations were mainly additive on all six species.

Widely varying weed densities that had been desiccated by freezing did not reduce combine efficiency (gathering plus threshing losses) in harvesting corn (Zea mays L., var. Nebraska 508), sorghum [Sorghum bicolor (L.) Moench, var. RS 610], or soybeans (Glycine max L., var. Ford). Average combine gathering losses with corn, sorghum, and soybeans were 2, 7, and 16%, respectively. Average threshing losses with the combine were less than 1% with corn and sorghum and less than 3% with soybeans. The high gathering losses in this study were due partly to delayed combining to allow the weeds to be desiccated by freezing temperatures.

Shoots of naturally established, foliated red maple (Acer rubrum L.) and persimmon (Diospyros virginiana L.) growing in North Carolina were treated with 2,4-dichlorophenoxyacetic acid (2,4-D) or 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) formulations following various shoot management procedures. Shoot management prior to treatment consisted of decapitating or not decapitating shoots at 2 inches above the ground line in May when the plants were 3 to 6 ft high. Herbicidal applications were made to uncut shoots and to resprouts of previously cut shoots at 30 and 60 days after decapitation. Responses measured 10, 14, and 22 months after treatment were percent control or original shoots, percent control of new shoots, shoot height, number of live stems/plant. The original shoot and new shoot values were averaged to provide a total shoot control index. Spraying of previously cut shoots at 30 or 60 days after cutting was more effective than spraying of uncut shoots except for 2,4,5-T applied to persimmon. The average total shoot control index for 2,4-D treated red maple, considering all rates, application dates, and evaluation dates was 82% for previously cut shoots and 56% for uncut shoots while the corresponding heights were 0.9 and 4.2 ft, respectively. For 2,4,5-T-treated red maple, the total shoot control indices were 92% and 78% for previously cut and uncut shoots, respectively, while the corresponding heights were 0.4 and 1.4 ft. For persimmon, there was a net advantage for treating previously cut shoots with 2,4-D, but the reverse was true for 2,4,5-T. The results are consistent with the theoretical behavior of 2,4-D and 2,4,5-T in woody plants outlined as a basis for conducting the study. Alternate explanations of results are proposed and practical implications described.