Plots were established in 1970 in the Nebraska Sandhills for the control of green sagewort (Artemisia campestris L.). Herbicides were applied in 1970; 1970 and 1971; 1970, 1971, and 1972; and 1970 and 1972. Nitrogen fertilizer at 45 kg/ha was applied in 1973. Herbicide treatments included 2,4-D amine [(2,4-dichlorophenoxy)acetic acid], 2,4-D ester, 2,4,5-T [(2,4-5-trichlorophenoxy)acetic acid], silvex [2-(2,4,5-trichlorophenoxy)propionic acid], and mixtures of picloram (4-amino-3,5,6-trichloropicolinic acid) or dicamba (3,6-dichloro-o-anisic acid) and 2,4-D amine. Herbicides were most effective for the control of broadleaf weeds when they were applied in 3 consecutive years or in alternate years. Herbicides applied only once did not effectively control broadleaf weeds. When nitrogen was applied after weed control treatments, weed production increased if herbicide applications were not effective. If weed control treatments were effective, nitrogen did not affect weed production.

Ammonium sulfate increased the magnitude and rate of 14C-picloram (4-amino-3,5,6-trichloropicolinic acid) absorption in detached strawberry guava (Psidium cattleianum Sabine) leaves. Absorption of 14C-picloram with or without ammonium sulfate leveled off at 6 to 12 hr. The magnitude of the ammonium sulfate-induced increase in 14C-picloram absorption was not affected by picloram concentration in the range 250 to 2000 ppmw, or by leaf age. The absorption of 14C-picloram was increased by 0.1, 0.5, 1.0, and 10% ammonium sulfate; 0.01% had no effect. Increased 14C-picloram absorption resulted from adding the ammonium salts of sulfate, nitrate, chloride, or dibasic phosphate, but ammonium sulfate was the only one of six sulfate salts to increase picloram absorption. A pH adjustment of the external solution from 6 to 4 increased picloram absorption, whereas a pH change from 6 to 8 had no effect. Both ammonium dibasic phosphate at a solution pH of 7.7 and ammonium monobasic phosphate at pH 4.6 increased picloram absorption, whereas potassium dibasic phosphate at pH 9.5 had no effect, and potassium monobasic phosphate at pH 4.6 did increase absorption.

X-ray fluorescence analysis (XFA) is a new method for the spatial localization and quantification of herbicide residue on leaf surfaces. The distribution pattern of propanil (3′,4′-dichloropropionanilide) on the surface of prune (Prunus domestica L.) leaves sprayed to simulate drift is easily mapped using XFA. Residue distribution maps may be electronically enhanced. Enhancement does not qualitatively change the information content of the map when done with discretion.

Adsorption of ethylene in four North Carolina soils and on montmorillonite, kaolinite, and organic matter was studied. Rate of ethylene diffusion through soils in the field and laboratory and its rate of loss from field soil were also examined. Ethylene was adsorbed in greater quantities on two soils which were limed as compared to their field pH. Ethylene adsorption by another surface soil and a subsoil were unaffected by pH changes. The order of adsorption of several hydrocarbon gases by two of the soils was ethylene = propylene ≫ methane ≥ ethane ≥ propane. Montmorillonite adsorbed more ethylene than did kaolinite or organic matter. Soils which adsorbed ethylene also had slower diffusion rates when ethylene was injected into a homogeneous soil column. Ethylene diffused 2.1 m horizontally and 0.7 m vertically to cause at least 50% witch weed (Striga lutea Lour.) seed germination in a Lakeland soil in the field. Witchweed seed germination as high as 90% was obtained at soil depths of 0.3 m and horizontal distances of 0.7 m from the point of ethylene injection.

Using a modified in vivo nitrate reductase assay, all photosynthetic inhibitors tested were shown to effectively block light-dependent nitrite reduction in green leaf tissue. Nitrate reduction continued so that nitrite accumulated. Nitrite, vacuum infiltrated into leaf tissue, disappeared linearly with time when incubated in the light. Nitrite, vacuum infiltrated with a photosynthetic inhibitor, did not disappear but accumulated to even higher levels. The degree of inhibition of nitrite reduction was a function of herbicide concentration and time of incubation.

Screening studies initiated in 1969 to determine the effectiveness and selectivity of herbicides for herbaceous weed control during the first growing season in American sycamore (Plantanus occidentalis L.) plantations indicated that simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], atrazine [2-chloro-4-(ethylamino)-6- (isopropylamino)-s-triazine], and dalapon (2,2-dichloropropionic acid) had the desired properties at economically feasible use rates. To further evaluate these herbicides and ametryne [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine], permanent plots were established in a sycamore plantation in 1970. Weed control obtained from a single herbicide application in the spring after planting seedlings in the winter has resulted in increased height, diameter, and volume growth of the sycamore for at least three growing seasons. No serious phytotoxicity on the crop species was noted with application rates from 4.5 to 9.0 kg/ha of the s-triazines alone or from 5.6 kg/ha of dalapon in combination with the lower rate of simazine and atrazine.

Glasshouse experiments were conducted to determine the phytotoxic effect of triallate [S-(2,3,3-trichloroallyl)-diisopropylthiocarbamate] granules on oat (Avena sativa L. ‘Kelsey’). The sphere-of-influence of the granules was found to diminish rapidly with increase in the horizontal distance from the tips of the caryopses. At a distance of 10 mm from the caryopsis tip there was no significant effect on the growth of the oat seedling. The need for the granules to be in close proximity to the developing coleoptile could not be counteracted by increasing the number of granules per caryopsis once the granules were 10 mm or more from the caryopsis. These results give cause to seriously question the generally held belief that triallate disperses through the soil in a volatile phase. Extension of the first leaf and mesocotyl was inhibited much more readily by triallate than coleoptile extension, which was stimulated by a number of treatments. When granules were left on the soil surface of sub-irrigated pots the phytotoxic effect seemed to be mediated through triallate-exposure of the coleoptile tip.

Simulated rainfall less than 8 hr after postemergence application of bentazon (3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2, 2-dioxide) reduced its activity on velvetleaf (Abutilon theophrasti Medic.) and common cocklebur (Xanthium pensylvanicum Wallr.) in greenhouse studies. In field studies, simulated rainfall less than 24 hr after application reduced bentazon's activity on velvetleaf. on common cocklebur, bentazon's activity was reduced even if simulated rainfall was delayed for more than 24 hr after application. In greenhouse studies, spray adjuvants (vegetable or petroleum oil) were helpful in overcoming the detrimental effects of simulated rainfall. Greenhouse and field studies indicated that soybeans [Glycine max (L.) Merr.] could tolerate bentazon-oil adjuvant combinations.

Three years of field experiments showed that Canada thistle. [Cirsium arvense (L.) Scop.] could be controlled with deeply injected soil fumigants without covering the soil with a tarpaulin. The degree of control depended on the kind of fumigant, the rate of application, and the depth of injection. Weed control with fumigants usually improved as the rate of application and depth of injection increased. The most effective treatment was 1,3-dichloropropene at 560 kg/ha injected to a depth of 46 cm. Good to excellent control of Canada thistle was also obtained with 1,3-dichloropropene at 280 kg/ha injected either 23 or 46 cm and ethylene dibromide at 160 kg/ha and chloropicrin + ethylene dibromide at 20 + 55 kg/ha injected at 46 cm. Results with ethylene dibromide and chloropicrin + ethylene dibromide were more erratic than with 1,3-dichloropropene. Increasing the percentage of chloropicrin in the combination reduced the control of Canada thistle.

Ten warm-season and six cool-season weed species were grown in the glasshouse on Hartsells fine sandy loam soil and Lucedale sandy loam soil at pH levels from 4.7 to 6.3. Growth of species varied widely in response to soil pH as measured by herbage yield. Showy crotalaria (Crotalaria spectabilis Roth), coffee senna (Cassia occidentalis L.), and large crabgrass (Digitaria sanguinalis (L.) Scop.] were highly tolerant to low pH soils. Sicklepod (Cassia obtusifolia L.), annual bluegrass (Poa annua L.), Carolina geranium (Geranium carolinianum L.), and buckhorn plantain (Plantago lanceolata L.), were medium to high in tolerance. Jimsonweed (Datura stramonium L.), tall morningglory [Ipomoea purpurea (L.) Roth], crowfootgrass [Dactyloctenium aegyptium (L.) Richter], and prickly sida (Sida spinosa L.) were medium to low in tolerance to low soil pH. Growth of Florida beggarweed [Desmodium tortuosum (Sw.) DC], redroot pigweed (Amaranthus retroflexus L.), chickweed [Stellaria media (L.) Cyrillo], common dandelion (Taraxacum officinale (Weber), and wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler] was severely reduced in soils with low pH.

Distribution patterns of foliar applied herbicides can be studied by x-ray element mapping provided the herbicide contains an atom with an atomic number of 11 (sodium) or greater. The suitability of an herbicide for element mapping increases as the number of similar detectable atoms per molecule increases. Herbicides containing one detectable atom per molecule provide usable element maps at concentrations of 1.12 kg/ha and higher. Inaccurate element maps can result from: (1) Formulation components containing detectable atoms the same as those of the active ingredient. (2) Herbicide volatility during analysis due to reduced pressures and heating. (3) Specimen topography preventing x-ray detection at some locations on the plant surface. (4) Herbicide concentrations that are below the minimum detectable limit. If adequate precautions are followed in the use of x-ray element mapping, a wide range of uses exist in weed science.

Field studies indicated that liming an acid Bladen silt loam from pH 5.5 to 7.5 increased the phytotoxicity of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and prometryn [2,4-bis-(isopropylamino)-6-methyoxy-s-triazine]. Liming greatly increased the persistence of atrazine, but did not affect prometryn dissipation. Liming increased the 14C-concentration present in the shoots of corn (Zea Mays L. ‘Pioneer 3369A’), cotton (Gossypium hirsutum L. ‘Coker 201’), and soybeans [Glycine Max (L.) Merr. ‘Ransom’] from soil treated with 14C-ring labeled atrazine, prometryn, and hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine] in greenhouse studies. Decreases in 14C-uptake by the crops were associated with adsorption and degradation of the compounds in the soil. Atrazine was taken up in much greater amounts than hydroxyatrazine. Cotton absorbed less of the s-triazines than soybeans or corn from soil.

In field studies, herbicides were applied at various times to different plots during the summer and fall at two locations over a 3-year period to control winter weeds in nonoverseeded bermudagrass [Cynodon dactylon (L.) Pers.] turf. Annual bluegrass (Poa annua L.) control was higher at Griffin for all herbicide applications made in October when compared with herbicide applications made at the same rate in July, August, or September. At Lawrenceville, optimum annual bluegrass control was obtained when bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl) benzenesulfonamide] was applied in August, terbutol (2,6-di-tert-butyl-p-tolyl methylcarbamate) applied in either August or September, benefin (N-butyl-N-ethyl-α,α,α-trifluoro −2,6 dinitro-p-toluidine) applied in September, pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl) benzamide] applied in either September or October, and simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] applied in October. DCPA (dimethyl tetrachloroterephthalate) did not control annual bluegrass satisfactorily at either location, regardless of dates of application. The control of several broadleaf weeds was generally higher when herbicides were applied in October at Griffin and when applied in September or October at Lawrenceville when compared with earlier treatments. Bensulide applied in October was the only herbicide that satisfactorily controlled parsley-piert (Alchemilla microcarpa Boissie Reuter).

Postemergence herbicide treatments that controlled tighthead sprangletop [Leptochloa panicoides (Presl) Hitchc.] and redstem (Ammannia auriculata Willd.), did not injure water-seeded rice (Oryza sativa L.), and substantially improved grain yields included: (a) a single application of propanil (3′,4′-dichloropropionanilide) at 4.5 kg/ha applied to weeds 8- to 10-cm tall; (b) two sequential treatments of propanil each at 3.4 kg/ha, with the first treatment applied to weeds 2- to 5-cm tall, and a second treatment applied 4 to 8 days later; (c) a tank mixture of propanil at 3.4 kg/ha and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] at 0.6 kg/ha, applied to weeds 8- to 10-cm tall; and (d) a tank mixture of propanil and molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate), each at 2.2 kg/ha, applied to weeds 8- to 10-cm tall. Treatments that controlled tighthead sprangletop or redstem unsatisfactorily or inconsistently and did not improve grain yields as much as more effective treatments included: preplant or postemergence treatments of molinate, or preplant treatments of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether), fluorodifen (p-nitrophenyl α,α,α-trifluoro-2-nitro-p-tolyl ether), CNP (2,4,6-trichlorophenyl-p-nitrophenyl ether), or He-314 (p-nitrophenyl-m-tolyl ether).

We evaluated nine systems of weed control over a 3-year period for cotton (Gossypium hirsutum L.) tolerance and control of weeds on Tifton loamy sand soil. Cultivation with sweeps did not control weeds effectively, which allowed weed competition to reduce cotton yields. Five cultivations plus an annual average of 185 hr/ha hand-hoeing was required to keep cotton relatively free of weeds for 7 to 8 weeks after planting. The use of herbicides offered certain economic advantages over systems using only cultural practices in controlling weeds. A preplant application of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) reduced annual hand-hoeing requirements by 66 hr/ha. The level of weed control at harvest time increased each year in all systems that used a herbicide program, but not where only cultivation or hand-hoeing was used. The continuous use of specific weed-control systems shifted weed populations. Systems that achieved 100% control by the end of the third year included all of the following: (a) a preplanting or at planting treatment of trifluralin or EPTC (S-ethyl dipropylthiocarbamate) plus (b) a preemergence application of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], (c) two directed postemergence sprays with MSMA (monosodium methanearsonate), and (d) diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. Large crabgrass [Digitaria sanguinalis (L.) Scop.] and Florida pusley (Richardia scabra L.) were nearly eliminated where we used trifluralin. Systems that did not include a postemergence application of MSMA allowed common cocklebur (Xanthium pennsylvanicum Wallr.), Florida beggarweed [Desmodium tortuosum (Sw.) DC], and other weeds to emerge and remain in the crop row, reducing yield of lint cotton. Cotton yield appeared to be directly related to the level of early-season weed control. We did not detect biologically active soil residues at harvest time each year. Our weed-control systems did not affect cotton fiber length, strength, or color.

Experiments were conducted to develop controls for cogongrass [Imperata cylindrica (L.) Beauv.] on noncrop areas. Single and multiple applications of herbicides were evaluated in field tests. All soil sterilants evaluated provided acceptable control. Single applications of TCA (trichloroacetic acid) at 56 kg/ha and dalapon (2,2-dichloro propionic acid) at 8.3 kg/ha controlled cogongrass without prolonged soil sterility. Multiple applications of amitrole (3-amino-s-triazole), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), glyphosate [N-(phosphonomethyl)glycine] and dalapon markedly reduced cogongrass stands 1 year after application.

Studies were conducted to compare weed growth under lighting systems composed of metal halide (MH) lamps and fluorescent-incandescent (FI) lamps. The MH lamps provided more light intensity and over a 6-week period caused plant dry weight to be 60 to 70% more than for plants exposed to the FI lamps. One week after emergence, all plants under the higher intensity MH lamps had larger stems and cotyledons or first true leaves. Six weeks after planting, weeds grown under the MH lamps had larger leaves, shorter internodes, thicker stems, and, in general, more pubescence than plants under the conventional lighting system. Growth habits of weeds exposed to the MH lamps were similar to those observed for field growth plants.

Cycloate (S-ethyl N-ethylthiocyclohexanecarbamate), applied by subsurface injection at 3.4 kg/ha, controlled 98 to 100% of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and 82 to 94% of common lambsquarters (Chenopodium album L.) and hairy nightshade (Solarium sarachoides Sendt.). Phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) at 1.1 kg/ha, applied after sugarbeets had emerged but before common lambsquarters had more than three pairs of true leaves or hairy nightshade had more than three or four true leaves, controlled the members of these species that had survived cycloate. Cycloate preconditioned sugarbeets and the surviving broadleaf weeds to injury be phenmedipham. Although applying phenmedipham following cycloate before sugarbeets had two pairs of true leaves sometimes resulted in severe crop injury, and applying it when weeds were too large resulted in incomplete weed control, in all experiments there was a period of at least 2 weeks during which application of phenmedipham killed the surviving lambsquarters and nightshade without injuring sugarbeets.

Field studies were conducted to evaluate the effectiveness of one, two, and three annual applications of atrazine [2-chloro-4-(ethylamino) −6-(isopropylamino)-s-triazine], 2,4-D [(2,4-dichlorophenoxy) acetic acid], dicamba (3,6-dichloro-o-anisic acid), and a three way mix of dicamba, mecoprop [2-[(4-chloro-o-tolyl) oxy]propionic acid], and 2,4-D at a ratio of 7:5:20 at different stages of development for the control of Canada thistle [Cirsium arvense (L.) Scop.]. Two consecutive annual applications in all atrazine treatments achieved the same level of control as cultivation every 5 weeks. In the year of the last treatment, Canada thistle was controlled with two or more consecutive annual applications of the hormone-type herbicides (2,4-D, dicamba, and the three way mix); however, in the year following the last treatment, regrowth occurred.

Analysis for total carbohydrate content was made on oven dried bermudagrass [Cynodon dactylon (L.) Pers.] dallisgrass (Paspalum dilatatum Poir.) and smutgrass [Sporobolus poiretii (R. & S.) Hitchc.] storage tissue collected at 2, 4, 6, or 36 weeks after fall treatment and at 2, 4, or 6 weeks after fall and spring treatment with three herbicides at varying rates. Those species that survived either fall or fall and spring herbicide application exhibited an initial reduction in carbohydrate content, but it returned to a level comparable to that in the untreated plants in most instances within 6 weeks after treatment. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 4.48 and 8.96 kg/ha and bromacil (5-bromo-3-sec-butyl-6-methyluracil) at 2.24 and 4.48 kg/ha resulted in carbohydrate reduction in bermudagrass and dallisgrass for no more than 6 weeks except where both fall and spring treatments were used. Smutgrass was controlled with these two herbicides within 2 weeks so that not enough live tissue was available for analysis. There was no carbohydrate reduction in bermudagrass with the 2.24, 4.48, or 8.96 kg/ha rates of MSMA (monosodium methanearsonate) beyond 2 weeks following treatment. The carbohydrate content of smutgrass was reduced up to 6 weeks after treatment with MSMA, and dallisgrass was controlled at all rates so that no carbohydrate analysis could be made.