The etymology of herbicide has been traced to a U. S. trademark originally registered by William J. Reade of the Reade Manufacturing Company.

A 2-year field study was conducted to determine the effects of periodic removal of topgrowth on tuber production and persistence of sago pondweed (Potamogeton pectinatus L.) in an irrigation canal. Plots were treated at 1, 2, and 4-week intervals throughout the irrigation season with aromatic solvent to kill the topgrowth. The tuber population was determined before the treatments began and at the end of each season. At the end of the first season, the number of tubers was reduced 78, 87, and 54% in the plots treated at 1, 2, and 4-week intervals, respectively. After two seasons, the number of tubers was reduced 91, 81, and 80%, respectively. All treatments controlled sago pondweed topgrowth effectively, but none eliminated the tubers completely.

Field plots of small well-rooted plants of yew [Taxus media Rehd., var. Hicks] and maple [Acer palmatum Thunb., var. Japanese maple] were treated annually for 3 years with 3-(3,4-dichlorophenyl)-1,1-dimethylurea [diuron], 2-chloro-4,6-bis(ethylamino)-s-triazine [simazine], 2-(2,4-dichlorophenoxy)ethyl sodium sulfate [sesone], dimethyl tetrachloroterephthalate [DCPA], isopropyl m-chlorocarbanilate [chlorpropham], α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine [trifluralin], 2-sec-butyl-4,6-dinitrophenol [dinoseb], and 3-amino-s-triazole [amitrole]. Commercial formulations of the herbicides were applied in water as a soil drench in May each year, at minimum effective dosage levels for weed control and at much higher levels. Diuron at herbicidally effective rates significantly reduced stand and growth of yew and maple plants. Simazine and sesone caused noticeable but variable reductions in growth of maple plants that were not statistically significant and yew plants were unaffected by these treatments. None of the other herbicides caused visible or measurable differences in growth.

Imbibed seeds of rough cinquefoil (Potentilla norvegica L.) remain dormant in darkness at constant and alternating temperatures. Full promotion of germination resulted after 3 days' dark imbibition at 25 C followed by 24 hr of continuous unfiltered fluorescent light. Germination was controlled by phytochrome. The sensitivity of the seeds to short light exposures was increased by the introduction of a temperature shift to 40 C for 2 hr, at the conclusion of the normal dark imbibition period at 25 C. The temperature shift also reduced the time required in continuous light to give full promotion of germination. The response to light was synergistically increased when the seeds were imbibed in 0.2% KNO3, and given the temperature shift. Nearly full promotion was reached with ca. 5 min of red light, and 50% germination occurred with as little as 1 sec. The system was still under phytochrome control. These findings suggest a mechanism by which soil populations of weed seeds may become physiologically conditioned to respond to very brief exposures to light.

The relative adsorption and migration of four thiocarbamate herbicides were studied in five soil types. Pebulate (S-propylbutylethylthiocarbamate) was adsorbed to the greatest degree by any one of the soils or adsorbents used. EPTC (ethyl N-N-dipropylthiocarbamate) showed the least adsorption while ethyl N-ethyl-N-cyclohexylthiocarbamate (hereinafter referred to as R-2063) was intermediate. Charcoal and bentonite clay were very effective adsorbents while the soils varied in their ability to adsorb the herbicides. A correlation was found between the rate of adsorption and the amount of organic matter in the soil. Such correlation was not found with the clay content, but a multiple regression test showed that the clay content is also closely associated with adsorption. The leaching of EPTC, pebulate, R-2063, and S-2,3-dichloroallyl N,N-diisopropylthiolcarbamate (diallate) in soil columns was directly related to their solubilities in water and inversely related to the organic matter content of the soil. Incorporation of the herbicides into the upper 5 cm of the soil did not alter the pattern or depth of their leaching. The lateral diffusion of thiocarbamates in the soil was much more restricted than the leaching downward. Again, this movement was closely related to the water solubilities of the herbicides, to soil organic matter, and apparently to the vapor pressures of the herbicides. EPTC vapor loss was the greatest followed in order by pebulate and R-2063. The rate of vapor loss from soils of all of the herbicides tested was reduced when the soil properties enabled rapid infiltration and drying of the spray drops.

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.

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.

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.

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.

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.

Doses of 1-(2-methylcyclohexyl)-3-phenylurea (siduron), sprayed on seeds of several forage, turf, and weed grasses on the soil surface killed some weed grasses without injuring many desirable grasses. Seeds of tolerant grasses mixed with an excess of a dry siduron formulation and stored for 12 months germinated without injury, but crabgrass (Digitaria sanguinalis (L) Scop.) and barnyardgrass (Echinochloa crusgalli (L.)) were killed during germination. Siduron eliminated seedling weed grasses from seedling perennial turfgrasses when applied on the soil surface or incorporated in the soil just before planting. When applied as a coating on seeds of turfgrasses at planting time, siduron controlled some annual weed grasses without injurying the turfgrasses. Herbicidal action appeared to be localized mainly in the grass roots and differed from that of 1,1-dimethyl-3-phenylurea (fenuron) and isopropyl carbanilate (propham) applied at equimolar doses.

The herbicide O-(2,4-dichlorophenyl) O-methyl isopropylphosphoramidothioate (DMPA) contains an asymmetric tetracovalent phosphorus. The d-isomer is much less active and the l-isomer more active than dl-DMPA in inhibiting seedling grass growth. Furthermore, low levels of dl-DMPA stimulate root growth of seedling wheat (Triticum vulgare L., var. Soft winter).

We studied the inactivation of herbicides applied to the soil by activated carbon in the greenhouse and field. Degree of inactivation depended upon herbicide type, dosage, plant species, and quantity of activated carbon applied. In greenhouse experiments with Toa silty clay, 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) was inactivated at activated carbon: herbicide ratios of 66:1, whereas 4-amino-3,5,6-trichloropicolinic acid (picloram) required ratios of 3600:1. Beans (Phaseolus vulgaris L., var. Black Valentine) were used as a bioassay. In the field, activated carbon rates up to 600 lb/A did not completely prevent injury to oats (Avena sativa L., var. Markton), cucumbers (Cucumis sativus L., var. Ashly), and Black Valentine beans by propazine at 2.5 lb/A in Toa silty clay 0, 37, 72, and 93 days after herbicide application. Activated carbon protected oats from picloram at 0.5 lb/A but did not completely protect cucumbers or beans at rates up to 600 lb/A. Activated carbon in untreated herbicide soils was not harmful to growth of beans, oats, and cucumbers in Toa silty clay.

Experiments were conducted to determine the effect of 3-(m-trifluoromethylphenyl)-1,1-dimethylurea (fluometuron) and 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne) on oxygen consumption by mitochondria isolated from the hypocotyls of soybean (Glycine max L., var. Lee) seedlings. Prometryne caused a decrease in second state 3 oxidation of both malate and succinate, but the decrease was overcome by 2,4-dinitrophenol (hereinafter referred to as DNP), indicating a response similar to that of oligomycin. Fluometuron caused an increase in second state 4 oxidation of both malate and succinate and overcame the inhibition of oxidative phosphorylation caused by oligomycin, indicating an uncoupling response similar to DNP. Fluometuron was also shown to reverse the inhibition of oxidative phosphorylation caused by prometryne. Concentrations of prometryne causing the 50% inhibitory response were somewhat higher than those reported for s-triazines on other tissues, while those for fluometuron were well within the inhibitory range reported for other substituted ureas.

An application of potassium nitrate or urea to the soil of detopped potted tomato plants [Lycopersicon esculentum Mill.] increased the rate of exudation from the stumps of the plants from 100 to over 300% and increased the concentration of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine [atrazine] in this augmented exudate from 9 to 40%. Atrazine applied to the soil at 2:00 PM was detected in the stump exudate within 10 min and with an application of 3500 μg per pot it was approaching its maximum concentration by the end of 3 hr. The build-up in the concentration of atrazine in the exudate occurred at a faster rate in plants treated with potassium nitrate than in water control plants. Increasing the soil temperature from 10 to 30 C increased the rate of exudation and at each temperature an application of potassium nitrate or of urea increased the concentration of atrazine in the augmented exudate. In addition to atrazine, 2-chloro-4,6-bis(isopropylamino)-s-triazine [propazine], 2-methoxy-4,6-bis(isopropylamino)-s-triazine [prometone], and 2-methoxy-4-ethylamino-6-isopropylamino-s-triazine [atratone] were applied at 1750 and 3500 μg/pot. The concentration of these triazines in the exudate increased directly with their solubility in water. An application of urea increased the concentration of all four triazines in the exudate.

Degradation of 2-chloro-4-ethylamino-6-isopropyl-s-triazine (atrazine) was studied in the 0 to 9, 14 to 24, and 36 to 48-inch depths of Sharpsburg silty clay loam and Keith silt loam soils. The effects of moisture, temperature, and microorganisms on degradation were observed. Atrazine was degraded two to three times faster in the topsoils than in the subsoils. Each 10 C temperature increase from 15 to 35 C caused the degradation rate to increase two to three times in these soils. Increasing the moisture content of the soils from 0.4 to 0.8 field capacity caused 14CO2 evolution from chain-labeled atrazine-14C treated soils to increase zero to six times. At 25 C and 0.8 field capacity, 100 to 194 atrazine molecules were detoxified for each molecule evolved as 14CO2 from chain-labeled atrazine. Solution culture studies showed cleavage of the side chain and ring of atrazine-14C except in the 14 to 24 and 36 to 48-inch depths of Keith silt loam.

Several investigations were undertaken to study the metabolism of alpha,alpha,alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) by intact peanut (Arachis hypogaea L.) and sweet potato (Ipomoea batatas L.) plants and crude extracts of these plants. Attempts also were made to determine the biological activity of three isolated degradative intermediates. Accumulated data indicated that trifluralin was degraded by both intact and crude extracts of these plants; the degradation pathway differing in each instance. In crude extracts of peanuts, the initial degradation product was an incomplete dealkylated derivative of the parent compound, alpha, alpha, alpha-trifluro-2,6-dinitro-N-propyl-p-toluidine. The initial degradation product formed in sweet potato crude extracts was a reduced derivative of trifluralin, N2,N2-di-n-propyl-3-nitro-5-trifluromethyl-o-phenylenediamine. All isolated degradation intermediates used in bioassay studies demonstrated root inhibition in cucumber (Cucumis sativus L.) at many of the concentration levels utilized. The greatest amount of root inhibition was observed in cucumber seeds germinated in alpha,alpha,alpha-trifluro-2,6-dinitro-N-(n-propyl)-p-toluidine.

Grain sorghum (Sorghum vulgare Pers.) was grown in combination with varying densities and durations of yellow foxtail (Setaria glauca (L.) Beauv.) during 1963-1965 at Manhattan, Kansas. Weed yield and competitive influence were greatest during the year of above-average rainfall and supplemental N fertility. Reduction in sorghum grain yield was due principally to a reduction in number of seeds per head. A 16-inch weed band on the crop row reduced soil moisture more than any other density treatment, but lesser weed densities reduced soil moisture below that of weed-free plots.

Grain sorghum (Sorghum vulgare Pers.) was grown in combination with varying densities and durations of tall waterhemp (Acnida altissima Riddell) during 1964 and 1965 at Manhattan, Kansas. As waterhemp density and duration increased, sorghum fodder and grain yields were reduced. Yields of both species and competitive influence of waterhemp were highest during the year of high rainfall and supplemental N fertility. The net competitive influence of waterhemp on sorghum grain was accounted for principally by reduced seed size. Competition for soil moisture in 1965 was greatest when weeds remained full-season, and was most pronounced early in the season at soil depths below 20 inches.

Both carrot (Daucus carota L.) and common ragweed (Ambrosia artemisiifolia L.) plants metabolized 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron). Traces of all of the following derivatives of linuron were detected in both plants: 3-(3,4-dichlorophenyl)-1-methoxyurea, 3-(3,4-dichlorophenyl)-1-methylurea, 3-(3,4-dichlorohenyl)urea, and 3,4-dichloroaniline. Differences in absorption and concentration of these derivatives were observed between carrot and ragweed plants. All of the above derivatives were phytotoxic to common ragweed plants except for 3-(3,4-dichlorophenyl)urea and 3,4-dichloroaniline, while none of the derivatives were phytotoxic to carrot. In carrot, 87% of the applied linuron was metabolized to nonphytotoxic derivatives compared to only 13% in common ragweed plants. It appears that a combination of differences in absorption, metabolism, and phytotoxicity of several of the metabolite derivatives of linuron to carrot and common ragweed plants may be the primary reason for differences in sensitivity of these two plants to linuron.