Greenhouse studies were conducted to investigate the basis for effective field control of yellow nutsedge (Cyperus esculentus L. var. esculentus) when atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-trizine] was applied late postemergence. Yellow nutsedge responded similarly to atrazine applied preemergence, early postemergence, or late postemergence. Yellow nutsedge growing with or without the presence of the mother tuber responded similarly to atrazine applied early postemergence. Atrazine application to the soil resulted in much greater yellow nutsedge injury than foliar application. The addition of oil enhanced atrazine activity when foliarly applied, but not when soil applied. Simulated rainfall immediately after postemergence applications enhanced yellow nutsedge control more than when simulated rainfall was delayed. The primary roots of yellow nutsedge appeared to be more important than other underground absorbing areas for atrazine uptake in young plants. Plants from tubers originating from lower soil depths produced secondary roots deeper, and these plants were less affected by atrazine applied preemergence than plants originating from tubers closer to the soil surface. A considerable reduction in atrazine activity was obtained when tubers were planted into soil 1 month after atrazine application.

Treatments that enhanced the germination of dormant seed of dwarf spikerush [Eleocharis coloradoensis (Britt.) Gilly] the most were chilling seed at 2 C for 3 months and then scarifying with sodium hypochlorite, scarifying seed and then chilling wet seed at 7 C for 3 months, or chilling wet seed at 2 C for 24 months. Percentage of germination for these treatments were 58, 56, and 65%, respectively. Scarifying seed with sodium hypochlorite after they had been chilled wet for 12 to 24 months at 2 C reduced germination. Other treatments that significantly enhanced germination were chilling seed wet for 4 months at 2 C, scarifying dry-stored seed with a 5.25% solution of sodium hypochlorite for 10 h, and soaking seed in concentrated hydrochloric acid for 24 min. These latter treatments resulted in germination percentages of 35, 33, and 35, respectively. Eighty percent of the viable seed usually germinated within 10 days, and when germination was poor, seed lacked embryos or were empty. Dormancy appeared to be due to an impermeable seed coat and not to a germination inhibitor.

Chlorophyll content of wheat (Triticum aestivum L. ‘Mericopa’) and corn (Zea mays L. ‘Merit’) treated with the herbicide fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)-phenyl]-4(1H)-pyridinone} and grown under high light intensity (10.8 klux), was markedly reduced. Corn and wheat germinated from seeds treated with 10 uM fluridone and grown for 6 days were almost completely bleached. Under low light intensity (108 lux) the influence of fluridone on chlorophyll production was greatly reduced. Under very low light intensity (21.5 lux) this influence was almost completely lost. The effect of light on the activity of fluridone suggests that the inhibition of carotenoid production may represent the mode of action of this herbicide. This study shows that the carotenoid content of wheat or corn drops dramatically when these plants are treated with fluridone.

Absorption and translocation characteristics of both root- and shoot-applied mefluidide N-[2,4-dimethyl-5-[[(trifluoromethyl) sulfonyl] amino] phenyl] acetamide were determined in soybean [Glycine max (L.) Merr. ‘Wells’], common cocklebur (Xanthium pensylvanicum Wallr.), and giant foxtail (Setaria faberi Herrm.). Absorption of 14C-mefluidide was greater through the foliage than the roots of all plant species. Rate of leaf absorption and translocation of 14C initially was greater in giant foxtail than in either soybean or common cocklebur, but these processes failed to increase greatly with time in giant foxtail. Absorption and translocation increased over time in soybean and common cocklebur. Soybean absorbed slightly greater quantities of 14C-mefluidide than common cocklebur, but by 8 days after labeling, common cocklebur translocated approximately 47% more radio-label out of the treated leaf than soybean. The foliar-applied 14C-label appeared to move in the phloem along with the assimilate stream in all species, mainly to areas of high metabolic activity. 14C was associated with the root systems and/or nutrient solutions of soybean and giant foxtail, but not of common cocklebur. Exuded material chromatographed as mefluidide. Movement of 14C-label in all root-treated plants appeared to be confined within the xylem with older tissue containing greater amounts of 14C than the younger tissue. Differences in selectivity between crop and weed species may be partially due to differential mefluidide absorption, translocation, and subsequent concentration in certain plant tissues.

Representative herbicides of the substituted ureas, uracils, s-triazines, benzonitriles, and bipyridyls, which are potent inhibitors of photosynthetic electron transport, markedly accelerated photooxidations (chlorophyll bleaching and lipid peroxidation) normally occurring in isolated intact chloroplasts. Other herbicides, which are not potent inhibitors of photosynthesis, did not accelerate photooxidations. The photooxidations, whether in the presence or absence of herbicides, were completely prevented by exogenously supplied NADH or NADPH but not by sucrose or mannitol. Herbicide-induced injury to barley (Hordeum vulgare L.) seedlings treated with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) was diminished by allowing the seedlings to absorb NADPH. These results provide additional support to the hypothesis that depletion of the source of reducing potential (NADPH) is responsible for chloroplast photooxidations and plant death following treatment with photosynthesis-inhibiting herbicides.

Granule, and in some cases, tablet and ball formulations of bromacil (5-bromo-3-sec-butyl-6-methyluracil), dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1,1-dimethylurea], and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethyl urea} were applied to three areas within 30 km of College Station in the Claypan Resource area of Texas. Woody species growing in the area included blackjack oak (Quercus marilandica Muenchh.), post oak (Quercus stellata Wangenh.), yaupon (Ilex vomitoria Ait.), winged elm (Ulmus alata Michx.), white ash (Fraxinus americana L.), mockernut hickory (Carya tomentosa Nutt.), and tree huckleberry (Vaccinium arboreum Marsh.). Granules were applied either broadcast or in rows at several intervals. Tebuthiuron was the most effective herbicide on oaks, winged elm, and white ash. Tebuthiuron and picloram were equally and most effective on yaupon, mockernut hickory, and tree huckleberry. Tebuthiuron + picloram at 2.2 + 2.2 kg/ha was the most effective herbicide treatment on huckleberry. However, a mixture of tebuthiuron + picloram (1:1 w/w) was usually no more effective than the same rate of tebuthiuron in the mixture applied alone. Tablet and ball formulations of karbutilate and tablet formulations of tebuthiuron were generally equally as effective as granules. Applications of picloram and tebuthiuron granules in rows 1.8, 3.0, 4.6, or 6.1 m apart gave control equal to broadcast applications except for picloram on yaupon. On yaupon all row spacing treatments of picloram were less effective than the broadcast treatment, whereas with tebuthiuron the 6.1-m spacing was least effective. Picloram and tebuthiuron granules applied in rows, approximately at 1.8-m intervals with a tractor, were as effective as granules applied by hand in straight rows.

Field experiments were conducted for a 3-yr period to determine the feasibility of planting an alternate crop on fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] treated cotton land in event that an adequate cotton (Gossypium hirustum L.) stand fails to materialize. Fluometuron treatments were 1.7 kg/ha on a treated area basis as a banded application, and 1.7 and 3.4 kg/ha as a broadcast application. Grain sorghum [Sorghum bicolor (L.) Moench ‘AKS-614’, ‘Excel’ and ‘BR 64’] and soybeans [Glycine max (L.) Merr. ‘Dare’ and ‘Lee 68’] were planted 3, 6, and 9 weeks after fluometuron application. Grain sorghum and soybean tolerance to fluometuron residues varied between locations. Very little injury occurred on the Sequatchie loam in Knoxville, Tennessee, but considerable injury occurred on the Memphis silt loam at Milan, Tennessee. The differences were attributed to higher rainfall during the first 3-week period and to higher organic matter and higher sand content at Knoxville. Nevertheless, at Milan, grain sorghum was successfully grown 3 weeks after the 1.7 kg/ha banded application, 6 weeks after the 1.7 kg/ha broadcast application and 9 weeks after the 3.4 kg/ha application. Soybeans, also at Milan, were partially injured when planted between the fluometuron (1.7 kg/ha) treated bands 6 weeks after application and 9 weeks after application when planted on the 1.7 kg/ha broadcast-treated areas.

Field and greenhouse tests were conducted from 1974 to 1976 to determine the most effective rate and number of applications of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] for the control of six morningglory (Ipomoea) species. Growth chamber studies were conducted to determine photosynthesisrespiration equilibrium points (PRE-points) on two morningglory species. These units were used to measure the duration of the phytotoxic effect of bentazon on these morningglories from both single and repeat applications. Declining PRE-points indicated declining bentazon toxic activity within the plant. A treatment of two applications of bentazon at 0.84 kg/ha applied at a 4-day interval beginning with 2-week-old morningglory plants was optimal for maintaining a high PRE-point level. In field and greenhouse studies the greatest toxicity, regardless of morningglory species, occurred with bentazon at 0.84 or 1.12 kg/ha applied at 14 days and repeated at 28 days after emergence and 0.56 kg/ha applied three times with the first application made 14 days after emergence. Differences in susceptibility of the individual species indicated the importance of proper species identification before bentazon applications.

The Persistence of substituted dinitroaniline herbicides in soil varied widely. First-order kinetics were used to describe the dissipation rates. Half-lives of the herbicides in moist soil ranged from 29 to 124 days in two soil types under greenhouse conditions. Flooding the soil significantly increased the dissipation rate of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine]. Dissipation rates of dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) and butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] were affected to a lesser extent by flooding. Volatilization of trifluralin, fluchloralin, and ethalfluralin [N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine] from Bosket sandy loam was reduced by flooding when compared to volatilization from the same soil with a moisture content equivalent to field capacity. Pendimethalin exhibited low volatility. The effect of flooding on dissipation rates is apparently not due to increased volatilization.

Field experiments were conducted from 1974 to 1977 at Redfield and Centerville, South Dakota, to evaluate the tolerance of soybeans [Glycine max (L.) Merr.] at different growth stages and five varieties of soybeans to dicamba (3,6-dichloro-o-anisic acid) and to determine dicamba residue in the foliage. Yield reduction occurred from applications when soybeans were flowering. Furthermore, germination was reduced by dicamba application at pod-fill. Dicamba residue was detected in foliage 7 days but not 18 days after application. Extent of dicamba use and drift occurrence was determined by a telephone survey of 159 farmers. Thirty-one percent of the farmers surveyed used dicamba in 1976.

The effects of diluent volume and calcium concentration on glyphosate [N-(phosphonomethyl] glycine] phytotoxicity were evaluated by adding 0.0, 0.0025, 0.005, 0.01, 0.02, and 0.04 M CaCl2 to 1.68 kg/ha glyphosate and applying at 130, 190, 375, and 750 L/ha to tall morningglory [Ipomoea purpurea (L.) Roth] plants that were 10 to 12 cm tall. Thirty days after treatment, glyphosate phytotoxicity was reduced by calcium at diluent volumes of 375 and 750 L/ha. Addition of a sulfonine red dye to the spray solution showed that at 130 L/ha, runoff from tall morningglory leaves was negligible. At 375 and 750 L/ha different volumes, ½ to ¾ of the spray solution, as measured by dye retention, ran off the leaf surface. At 750 L/ha, the water and dye collected at the leaf margins and the spray pattern on the leaf surface was not uniform.

Our purpose was to investigate the influence of growth reserves of perennial range grasses on their tolerance to applications of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Competing annual grasses were removed with atrazine treatment at 1.1 kg/ha. The carbohydrate reserves of the perennial grasses were reduced by mowing the previous season. Crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.] plants with reduced carbohydrate reserves, as indicated by reduced etiolated growth, were less tolerant to atrazine than their nonmowed counterparts. Without reduced carbohydrate reserves, squirreltail [Sitanion hystrix (Nutt.) J. G. Smith] was much more susceptible to atrazine than crested wheatgrass. Thus, the weed control treatment did not necessarily increase the density of desirable perennial grasses.

Tall morningglory [Ipomoea purpurea (L.) Roth.], pitted morningglory (I. lacunosa L.), ivyleaf morningglory [I. hederacea (L.) Jacq.] and entireleaf morningglory (I. hederacea var. integruiscula Gray) were compared for their competitive ability with cotton (Gossypium hirsutum L.) at weed densities of 4, 8, 16 and 32 weeds/15 m of row. Tall morningglory was the most competitive with yield reductions of as much as 88% at 32 weeds/15 m. The higher populations of tall morningglory also significantly reduced cotton populations, mechanical harvesting efficiency and lint percentage below that in the controls. Pitted morningglory densities twice that of tall morningglory were required to produce cotton responses similar to those induced by tall morningglory. Ivyleaf morningglory and entireleaf morningglory were almost identical in their competitive potentials and were less competitive than the other species evaluated. Their competitive ability was greatly reduced by disease. Competition from morningglories did not consistently affect cotton fiber micronaire, fiber length or strength.

Terbacil (3-tert-butyl-5-chloro-6-methyluracil) was applied to highbush blueberry plants (Vaccinium corymbosum L. ‘Pemberton’, ‘Rancocas', ‘Jersey’, and ‘Concord’) growing in a Rifle peat, Camas clay loam, or Mossy Rock silt loam for control of quackgrass [Agropyron repens (L.) Beauv.]. Control was 80 to 100% from applications made in April after the blueberry plants broke dormancy. Higher dosages proved phytotoxic from these applications on Camas clay loam. Applications in February or March while the blueberry plants were still dormant caused no phytotoxicit; to the blueberry plants and provided 80 to 90% quackgrass control. Four consecutive yearly applications caused no residual buildup to the point of phytotoxicity to blueberry plants. Carry-over of terbacil in the soil from year to year did occur.

Annual herbicide treatments are usually necessary for acceptable control of grassy weeds in turfgrasses and it is important that repeated treatment do not injure the turf. Seven herbicides were applied annually for 4 yr at recommended and three times recommended rates to ‘Emerald’, ‘Meyer’, and ‘Matrella’ zoysia (Zoysia spp.) and three herbicides were applied annually for 3 yr at similar rates to Tifway′, ‘Tifgreen’, ‘Tifdwarf’ and ‘Ormond’ bermudagrass [Cynodon dactylon (L.) Pers.]. Herbicide treatments delayed early spring green-up of Emerald and Matrella slightly more than Meyer zoysia when compared with respective untreated checks. Four annual treatments of napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] and profluralin [N-(cyclopropylmethyl)-a,a,a-trifluoro-2, 6-dinitro-N-propyl-p-toluidine] reduced the cover of Meyer more than Emerald or Matrella when final ratings were made. The 10.1 kg/ha rate of prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} and benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) also reduced the cover of Meyer. Profluralin at 10.1 kg/ha was the only treatment that reduced the stand of Matrella and none of the treatments reduced the stand of Emerald. The 10.1 kg/ha treatments of profluralin and prosulfalin reduced the stand of Tifgreen, Tifdwarf, and Ormond more than Tifway bermudagrass. None of the herbicide treatments reduced the stand of Tifway.

Yields of birdsfoot trefoil (Lotus corniculatus L.) and red clover (Trifolium pratense L.) were increased during establishment after herbicide treatments. All treatments, which included preplanting application and incorporation of EPTC (S-ethyl dipropylthiocarbamate) at 2, and 4 kg/ha in all combinations with postemergence applications of dinoseb (2-sec-butyl-4,6-dinitrophenol) at 0.25 and 0.5 kg/ha, controlled weeds and increased yields over those of untreated plots during a 2-yr period. EPTC and dinoseb treatments alone and in combinations were economical in birdsfoot trefoil, using the cost for weed control and the value of the extra forage. However, with red clover only dinoseb proved economically feasible at hay prices less than $80/metric ton.

Survival of hydrilla (Hydrilla verticillata Royle) plants and propagules after removal from water and desiccation under controlled conditions were studied. Both apical and sub-apical sections of hydrilla plants were physiologically alive after drying for 16 h at 30 C and 40% relative humidity. Tubers survived drying conditions longer than turions. There was 16.7% sprouting in tubers that had been dried for 64 h, while percent sprouting of turions decreased sharply as the drying period increased from 0 to 8 h.

Vapor pressures of technical-grade triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate] were calculated from the vapor density measurements determined at seven different temperatures, using a gas-saturation technique and solid adsorbent traps. The equation Log10P = 11.05 – (4401/T) delineated the relationship between the apparent vapor pressure and temperature, giving the triallate vapor pressure values from 1.083 × 10−4 to 16.371 × 10−4 mm Hg over the temperature range of 20 to 45 C. The vapor flux of triallate from glass surfaces was of the order of 5.7 μg cm−2 h−1 at 25 C.

Toxicity of nonradiolabeled and translocation of 14C-labeled glyphosate [N-(phosphonomethyl)glycine] in cotton (Gossypium hirsutum L.) were evaluated under different environmental conditions as affected by surfactant and by the maturity of the plant tissue at the place of herbicide application. Toxicity was affected primarily by temperature with 21 to 40% greater cotton injury at 25 C than at 35 C. The addition of surfactant often increased toxicity under environmental conditions where toxicity was initially low. Absorption and translocation of 14C was affected primarily by relative humidity (RH). At constant temperature and rate of surfactant, an increase in RH from 40 to 100% resulted in a 3- to 6-fold increase in translocation of 14C. Autoradiograms indicated that the movement of the 14C-label was primarily into leaves above the treated area. Translocation of 14C was significantly greater following application to the mature lower stem than to the mature lower leaves or to immature upper stem or leaves of cotton.