Aqueous solutions of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone}, VEL 3510 {1-β,β-dimethoxyethyl-1-methyl-3-[5-(1,1-dimethylethyl)-1,3,4-thiadazol-2-yl] urea}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadazol-2-yl]-N,N′-dimethylurea}, fluridone 1-methyl-3-phenyl-5-[3-trifluoromethyl)phenyl]-4(1H)-pyridinone, metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], and prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] were spectrophotometrically titrated to obtain pKA values. Ionizing properties of the chemicals were compared with other related compounds reported in the literature. The pKA values for the six herbicides were 0.6 and 11.3, 0.9 and 9.0, 1.2, 1.7, 1.1, and 4.1, respectively.

Retention, absorption, translocation, and volatility of foliarly applied diclofop-methyl {methyl 2-[4-(2,4-dichlorophenoxy) phenoxy] propanoate} were compared in barnyardgrass [Echinochloa crus-galli (L.) Beauv.], a susceptible grass; proso millet (Panicum miliaceum L.), a moderately susceptible grass; longspine sandbur [Cenchrus longispinus (Hack.) Fern.], a tolerant grass; and soybean [Glycine max (L.) Merr. ‘Hark’] and cucumber (Cucumis sativus L. ‘Green Star’), both tolerant broadleaf plants. On a jug/plant basis, the order of diclofop-methyl spray retention was cucumber > soybean > proso millet > longspine sandbur = barnyardgrass. On a μg/mg dry weight basis, proso millet retained 3 to 10 times more diclofop-methyl than all other species. One day after treatment (DAT), absorption of 14C-diclofopmethyl was 14 to 18% less in longspine sandbur than in the other species, 3 DAT absorption in cucumber was 8 to 14% greater than in the other species, and 5 DAT absorption in soybean was 3 to 12% less than in other species. Translocation of 14C-diclofop-methyl did not differ among species, with 98% of the applied radioactivity located in the treated leaf. An average of 11% of radioactivity applied to the surface of intact, living plants and excised, dried leaves of cucumber, soybean, and barnyardgrass, as well as glass cover slips, was lost by evaporation. None of the parameters measured showed differences large enough to be implicated as primary selectivity mechanisms.

Adsorption isotherms were obtained for buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone}, VEL 3510 {1-β,β-dimethoxy-1-methyl-3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]urea}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4 (1H)-pyridinone} on soil organic matter (H- and Ca-saturated), Ca-montmorillonite, and Cape Fear sandy loam soil. Prometryn [2,4-bis (isopropylamino)-6-(methylthio)-s-triazine] was included as a reference. The order of adsorption on all adsorbents was fluridone ≥ prometryn > > tebuthiuron ≥ VEL 3510 > buthidazole. Fluridone adsorption on the various adsorbents was: H-organic matter > Ca-montmorillonite > Ca-organic matter > > Cape Fear sandy loam. Tebuthiuron, VEL 3510, and buthidazole adsorption on the various adsorbents was in the order: H-organic matter > Ca-organic matter = Ca-montmorillonite > Cape Fear sandy loam. Adsorption of all herbicides increased with decreasing pH, suggesting that the adsorption mechanism was molecular under neutral pH conditions and ionic under acidic conditions. All of the herbicides were adsorbed in high amounts as protonated species on IR-120-H cation exchange resin and in low amounts as molecular species on IR-400-Cl anion exchange resin. Buthidazole and VEL 3510 were adsorbed in high amounts as anionic species by the IR-400-Cl exchange resin at high pH levels.

Nitrate reduction on a leaf fresh weight basis was measured in common lambsquarters (Chenopodium album L.) and redroot pigweed (Amaranthus retroflexus L.) in individual leaves as a function of the photosynthetic photon flux density (PPFD) under which the plants were grown. Common lambsquarters had greater rates of nitrate reduction than did redroot pigweed regardless of leaf age or PPFD and responded to a significantly greater degree when PPFD was increased, with a proportionately greater increase in nitrate reduction among younger leaves.

Increased osmotic potential from 0 to −14 bars decreased the moisture uptake and germination of mechanically scarified hemp sesbania [Sesbania exaltata (Raf.) Cory] seed. Germination percentage for osmotic potential of 0, −2, −4, −6, and −8 bars was 86%, 86%, 70%, 19%, and 1%, respectively. This response to moisture stress was modified by imbibition, or hydration-dehydration, of the seed prior to the moisture stress. Imbibing the seed for as little as 2 h significantly increased its subsequent germination against moisture stress. One hydration-dehydration cycle had little or no effect on germination, but as the number of cycles increased, the germination percentage decreased. Prolonged hydration of 3 and 7 days followed by dehydration greatly reduced subsequent seed germination.

In field studies, postemergence applications of HOE 29152 {2-[4-(trifluoromethyl phenoxy)phenoxy] propanoate} at rates of 1.68 to 3.36 kg/ha effectively controlled quackgrass [Agropyron repens (L.) Beauv.] when applied to plants in the one- to three-leaf stage. Control was still effective the following year. The addition of a surfactant to HOE 29152 did not increase quackgrass control, but it did increase soybean [Glycine max (L.) Merr.] injury. Cultivation 1 or 7 days after herbicide application increased the efficacy of HOE 29152 on quackgrass. Due to abundant moisture in 1977, untreated quackgrass-infested plots yielded as much as the weed-free plots. However, in 1976, a very dry year, the control of quackgrass with HOE 29152 resulted in greatly increased soybean yields. In greenhouse studies, postemergence applications of HOE 29152 at rates of 0.56 to 3.36 kg/ha effectively killed rhizome buds and reduced shoot dry weights of quackgrass. The phytotoxicity of HOE 29152 at 0.56 kg/ha was less at a postspray temperature of 36 C than at 17 or 27 C; however, the phytotoxicity of HOE 29152 at rates of 1.68 and 3.36 kg/ha was similar at all three temperatures. HOE 29152 can volatilize from soybean leaves, with volatility greater at 38 C than at 21 C. Postemergence applications injured soybeans similarly in field and growth chamber studies. Injury was observed only on leaves that were expanded at time of treatment, was short-term, and was most prevalent at 3.36 kg/ha.

The production of new shoots of American pondweed (Potamogeton nodosus Poir.) and sago pondweed (P. pectinatus L.) was reduced significantly when winterbuds and tubers of these species were planted in dwarf spikerush [Eleocharis coloradoensis (Britt.) Gilly] sod. In most instances, the number of shoots produced was several times greater when winterbuds and tubers were planted in bare soil than when planted in spikerush sod. Similar results were obtained when the pondweeds were grown in separate aquaria, each aquarium being exposed to 500 ml of leachate per day from spikerush sod. The differences in reproduction of pondweeds could not be attributed to altered water quality nor to reduced levels of nutrients. No appreciable allelopathic response was elicited by the pondweed plants originating from planted tubers or winterbuds. The principal response appeared to be reduction in numbers of new shoots produced from the original propagules, although the reduction in biomass of the pondweeds exposed to the effects of spikerush was obvious. Of the two pondweeds investigated, sago pondweed was most sensitive to the influence of spikerush.

Responses of the vegetative growth of cogongrass [Imperata cylindrica (L.) Beauv.] to temperature and photoperiod were studied in plants grown from stem and rhizome propagules collected from plants originating at four locations in southern Alabama and Mississippi. The plants were grown in four controlled-environment chambers with day/night temperature regimes of 23/17 C and 29/23 C, photoperiods of 12 h and 16 h, and photosynthetic photon flux densities (PPFD) of 650 μE(einsteins)m−2s−1. After 87 days, heights, leaf areas, total dry weights, rhizome numbers, and rhizome dry weights were significantly greater in plants grown at 29/23 C than at 23/17 C. Total dry weights, rhizome numbers, and rhizome dry weights were greater at the 16-h photoperiod than at 12 h. Plants grown from propagules from the McNeil, Mississippi population, which originated from an introduction from the Philippines, were significantly smaller than plants grown from propagules collected from populations thought to have originated from an introduction of cogongrass from Japan. Mathematical analysis of the growth data showed that the observed differences in dry matter production were more closely related to differences in leaf area duration than to differences in net assimilation rate.

The effects of ethylene upon germination of common cocklebur (Xanthium pensylvanicum Wallr.) and redroot pigweed (Amaranthus retroflexus L.) seeds were studied. In laboratory tests with seeds in sealed flasks in the dark, 10 μl/L ethylene increased germination of redroot pigweed seeds from 7% to 52% at 30 C, and increased germination of large and small common cocklebur seeds from 30% and 0% to 100% and 90% respectively, at 25 C. At least 12 h of exposure to ethylene was necessary for appreciable stimulation of germination. In growth chamber studies with known numbers of seeds in pots of soil, ethylene at 11 kg/ha was injected into the soil, and the pots were enclosed in plastic bags for 24 h. One such injection at 2 weeks after planting, and successive injections at 2, 3, and 4 weeks, significantly increased redroot pigweed seedling emergence, and significantly decreased the numbers of dormant, viable seeds remaining in the soil. When pots were not enclosed, injections did not significantly effect redroot pigweed seeds, but significantly increased common cocklebur seedling emergence and decreased the number of viable common cocklebur seeds remaining in the soil.

The single-celled green alga Chlamydomonas eugametos was found to be well suited for detecting growth inhibitor activity of chemicals. Tests consisted of solubilizing technical grade compounds in 20-ml aliquots of a 1 × 105 cells/ml zoospore culture. Commercially available growth inhibitor herbicides significantly inhibited synchronous cell population increases within 48 h at concentrations ranging from 1 × 10−4 to 1 × 10−7M. Examples of compounds that inhibited Chlamydomonas more than 50% were butylate (S-ethyl diisobutylthiocarbamate) and diallate [S-(2,3-dichloroallyl)diisopropylthiocarbamate] at 1 × 10−4M, CDEC [2 chloroallyl diethyldithiocarbamate] and propham (isopropyl carbanilate) at 1 × 10−5M, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] and trifluralin [α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine] at 1 × 10−6 M, and bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate] at 1 × 10−7M. Ethanol, dimethylsulfoxide (DMSO), or acetone can be used to solubilize herbicides in the aqueous medium. DMSO and ethanol are not detrimental to the cells if the concentration is kept at 1% v/v or less.

Preliminary greenhouse studies indicated the presence of a synergistic interaction between low rates of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] or diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] in combination with linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] or chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea]. In a 3-yr field study, moderate injury of cotton (Gossypium hirsutum L. ‘Stoneville 213’) with no yield reduction was observed with fluometuron or diuron at 1.68 and 1.12 kg/ha, respectively, but higher rates (5.04 and 3.36 kg/ha, respectively) caused injury and yield reductions. Soybean [Glycine max (L.) Merr. ‘Hill’] injury ratings during the second year indicated a synergistic interaction between residue from fluometuron at 5.04 kg/ha combined with linuron at 2.48 kg/ha or chlorbromuron at 3.85 kg/ha, and from diuron at 3.36 kg/ha combined with linuron at 2.48 kg/ha. These interactions were not apparent in soybean yield data. Soybean injury the third year ranged from 30 to 60% with single or repeated applications of linuron or chlorbromuron, although yields were not affected. Residual fluometuron and diuron from 2 yr of application at 5.04 and 3.36 kg/ha, respectively, injured soybeans, but did not reduce yields. Significant synergistic interactions were observed through injury and yield measurements after two annual applications of fluometuron at 5.04 kg/ha combined with linuron or chlorbromuron. A synergistic interaction was detected in soybean yields with chlorbromuron at 3.85 kg/ha preceded by two annual applications of diuron at 3.36 kg/ha. Such interactions may occur under field conditions, but are unlikely to be economically significant. Chemical analysis indicated little evidence of accumulation, even with repeated application of fluometuron or diuron at 5.04 and 3.36 kg/ha, respectively.

Root growth of three zoysia (Zoysia spp. ‘Emerald’, ‘Meyer’, and ‘Matrella’) cultivars and four bermudagrasses [Cynodon dactylon (L.) Pers. ‘Tifway’, ‘Tifgreen’, ‘Tifdwarf’, and ‘Ormond’] was determined after several consecutive annual herbicide treatments. Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] reduced the root growth of all zoysia and bermudagrass cultivars. Prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} retarded root growth of Tifgreen and Tifdwarf bermudagrass when treated at any rate. Tifway and Ormond bermudagrass and zoysia cultivars were retarded at the 3X rate (10.2 kg/ha). Zoysia grass roots were not affected by oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one], bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide], or benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) treatments. DCPA (dimethyl tetrachloroterephthalate) and oxadiazon did not reduce root growth of bermudagrasses, except when Tifgreen was treated with oxadiazon at 3X rate (13.4 kg/ha).

Two yr of field research were conducted to evaluate the efficacy of BAS-9021 {2-[1-(N-allyloxyamino)butylidene]-5,5-dimethyl-4-methoxycarbonylcyclohexane-1,3-dione, Na salt}, HOE 29152 {methyl 2-[4-(4-trifluoromethylphenoxy)phenoxy]propanoate}, and mefluidide N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide as selective herbicides applied postemergence to johnsongrass [Sorghum halepense (L.) Pers.]. All three herbicides afforded 85% or greater control of rhizome johnsongrass in one experiment in 1977, where repeat applications were made and ideal growing conditions prevailed. HOE 29152 also afforded excellent control with a single application made at the boot stage of johnsongrass. In a second experiment in 1977, when drought conditions prevailed, HOE 29152 was the only herbicide that afforded 70% or greater control of the johnsongrass. Both BAS-9021 and mefluidide afforded less than 60% control of johnsongrass in the single 1978 experiment, when evaluated at the end of the season. This study also was subject to drought conditions throughout the growing season.

Loss in activity of foliar-applied methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} occurred under low soil moisture conditions. A loss in control of yellow foxtail [Setaria lutescens (Weigel) Hubb.], wild oats (Avena fatua L.), little-seed canarygrass (Phalaris minor Retz.), and barnyardgrass [Echinochloa crus-galli (L.) Beauv.], was observed under greenhouse and growth chamber conditions. When soil was maintained at 2 to 3% above wilting point as compared to near field capacity, herbicide activity was decreased by 15 to 50%. High soil moisture (at or above 67% of field capacity) for at least 2 to 4 days following treatment was needed to achieve maximum effectiveness of the herbicide. Daily furrow irrigations for a period of 10 days following treatment of barnyardgrass in the field resulted in highest activity as compared to that under single irrigation regimes within the 10-day period. The effect of low soil moisture was minimized by increased rates of herbicide application. Hoe-29152 {methyl-2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoate} showed similar losses in activity associated with low soil moisture. No consistent changes in uptake or translocation of 14C-labeled diclofop could be detected in association with altered soil moisture status.

Field evaluations for control of grass species were conducted with metriflufen, the methyl ester of {2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid}, applied as preemergence and postemergence treatments. The preemergence application of 0.28 kg/ha gave 84 to 100% control of all species except grain sorghum [Sorghum bicolor (L.) Moench], johnsongrass [Sorghum halepense (L.) Pers.], red rice (Oryza sativa L.), and green foxtail [Setaria viridis (L.) Beauv.]. These species required 0.84 kg/ha for at least 95% control. At the three-leaf stage, all species except cheat (Bromus secalinus L.) and red rice were highly susceptible to the herbicide at 0.56 and 0.84 kg/ha. At the six-leaf stage, 0.56 kg/ha of metriflufen gave 96% control of Texas panicum (Panicum texanum Buckl.) and goosegrass [Eleusine indica (L.) Gaertn.], but 0.84 kg/ha was necessary for 92% control of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and 85% control of large crabgrass [Digitaria sanguinalis (L.) Scop.]. Except for cheat, metriflufen gave less than 55% control if applied when grasses were heading. Little postemergence control was evident for red rice.

Germination responses of redroot pigweed (Amaranthus retroflexus L.) seeds to temperature, water potential, atmospheric ethylene and carbon dioxide concentrations, light, and nitrate ion were examined individually. Seeds kept in dry storage at −20 C and tested within 2 yr of harvest germinated at 35 C (12 to 25%) or 39.5 C (40 to 65%), but only 0 to 2% at 30 C and below. Germination at 35 C was prevented by water potentials below −4 bars. When seeds were kept in dry storage at 24 to 28 C, afterripening became evident within 2 months. After storage at this temperature for 4 yr, seeds showed 38% germination at 14 C, 40% at 35 C and −8 bars water potential, and over 90% under more favorable conditions. Ethylene (1 to 100 ppmv) or continuous light enhanced germination at 30 C regardless of degrees of afterripening, although the ethylene effect was most dramatic in nonafterripened seeds. Ethylene at 100 ppmv caused 40% germination in these seeds, compared to 1% for controls. Neither carbon dioxide (0.001 to 4.5% v/v) nor dissolved potassium nitrate (0.02 to 0.2% w/v) influenced germination. These results are discussed in relation to environmental factors influencing field emergence of redroot pigweed.

We developed a technique to measure the projected leaf area of plants any time during the day or night. “Projected leaf area” is the leaf area seen from directly above, and is the area most likely to intercept herbicide spray from an over-the-top application. The technique involves photographing a plant and a reference square of known area from directly overhead using a light-tight box containing a flash unit. Negative images thus obtained are reflected (by means of a slide projector and mirror) onto filter paper lying on a glass stage. The projected leaf area is determined by planimetry of the negative image of the leaves and the reference square. The projected leaf area can be compared to the actual total leaf area after one determines the latter with a conventional area meter.

Sicklepod (Cassia obtusifolia L.) leaves and leaflets changed their orientation throughout 24-h periods. These endogenously controlled rhythmic movements resulted in dramatic changes in the percent projected leaf area (PPLA), the leaf area observed from directly above and expressed as a percentage of the total actual leaf area. The PPLA of sicklepod varied more than seven-fold throughout a 24-h period, being greatest during the day and least at night. Control of sicklepod with linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] applied postemergence at intervals throughout 24-h periods was greater from daytime applications than from late evening, night, and early morning applications. Percent control was highly correlated with PPLA, suggesting that rhythmic leaf movements and the resulting change in PPLA could be an important factor in determining the efficacy of postemergence herbicide applications on sicklepod by altering the area of the leaf surface most likely to intercept and retain herbicide spray from an over-the-top application. In addition to endogenously controlled leaf movements, we observed leaf movements caused by simulated cloud cover (80% shading). Shading increased the PPLA of sicklepod, suggesting that more leaf surface might be exposed to an over-the-top spray during cloudy periods than during sunny periods.

Roots of 10- and 14-day-old seedlings and excised leaves of cotton (Gossypium hirsutum L. ‘Coker 310’), jimsonweed (Datura stramonium L.), peanuts (Arachis hypogaea L. ‘Florigiant’), and prickly sida (Sida spinosa L.) were treated with ring-labeled 14C-tetrafluron {N,N-dimethyl-N′-[3-(1,1,2,2-tetrafluoroethoxy)phenyl] urea} in liquid culture. Herbicide absorption and subsequent translocation were limited in peanuts, intermediate in cotton, and very high in jimsonweed and prickly sida. Absorption of 14C-tetrafluron increased with time in 10- and 14-day-old seedlings. After 6 h, 10-day-old jimsonweed had absorbed as much as 50% of the initial 10-μg dose, whereas peanuts absorbed only 10%. Almost 100% uptake was observed after 48 h with 14-day-old seedlings of jimsonweed and prickly sida. Methanol-extracted 14C increased with time, and was higher for the weeds than for the crops. Only a small fraction of methanol-insoluble radioactive material was obtained, with the largest value in 14-day-old cotton at 48 h (3.0%). Autoradiographs demonstrated more rapid translocation of radioactivity from roots to shoots in jimsonweed and prickly sida than in cotton and peanuts. Limited absorption and translocation of tetrafluron in seedlings of peanut and cotton, and the rapid absorption and subsequent accumulation of high concentrations in seedlings of jimsonweed and prickly sida, are proposed to explain the selective action observed.

Glyphosate [N-(phosphonomethyl)glycine] applied to cranberry (Vaccinium macrocarpon Ait.) as a spray at 4 kg/ha in March controlled aster (Aster subspicatus Nees) 77 to 87%. Glyphosate swab treatment with 6% solution in July or August, 1978 controlled spirea (Spiraea douglasii C.) 90%. A single application of terbacil (3-tert-butyl-5-chloro-6-methyluracil) in April, 1976 at 2 kg/ha controlled inflated rush (Carex vesicaria L.) 70% for 3 yr. Phytotoxicity was not observed on ‘McFarlin’ cranberry vines from any of these glyphosate or terbacil applications. Phytotoxicity did result from April, July, or August spray applications of glyphosate. Swab treatments did not cause any injury to cranberry.