Glanded and non-glanded isogenic lines of cotton [Gossypium hirsutum L., var. Empire 61(WR)] were treated with 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) to determine the significance of lysigeneous glands in the tolerance of atrazine by cotton. The presence of lysigeneous glands did not increase atrazine tolerance by cotton or decrease the inhibition of photosynthesis by the herbicide. Detoxication of atrazine by N-dealkylation occurred in both glanded and non-glanded cotton. No significant difference in atrazine metabolism was observed between the two lines. Atrazine metabolism may be a more important factor than the presence of lysigeneous glands in the intermediate tolerance of cotton to atrazine.

Data were collected on 36 variables including application, environmental, edaphic, and plant conditions during a 3-year study of aerial brush control treatments at 79 sites. These then were correlated with defoliation responses of blackjack oak (Quercus marilandica Muenchh.) and post oak (Quercus stellata Wangenh.) to (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T). The stage of oak growth was of primary importance in obtaining maximum defoliation with 2,4,5-T; the oaks were most susceptible 6 to 8 weeks after the last killing frost. Air temperatures above 90 F, relative humidity below 60%, poor spray coverage and swath widths greater than 50 ft significantly reduced defoliation by 2,4,5-T. Total rainfall during the month before spray application was positively correlated with defoliation by 2,4,5-T, but correlations with rainfall for other time intervals before and after spraying were not significant. Wind above 6 mph at the time of treatment slightly reduced 2,4,5-T effectiveness, but wind direction and dew at spray time did not influence herbicide activity. Application rates of less than 1.75 lb/A were not as effective as higher rates. Aircraft design, spray-water carrier constituents, soil type, soil depth, soil temperature, and topography had no apparent influence on defoliation of oaks by 2,4,5-T.

The herbicides 3-tert-butyl-5-chloro-6-methyluracil (terbacil) and isopropyl m-chlorocarbanilate (chlorpropham) showed greatly enhanced activity on giant foxtail (Setaria faberii Herrm.) and ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.) when applied in an isoparaffinic oil rather than water. The activity of terbacil was enhanced but to a lesser extent when crop oil was added to a water carrier at a concentration of 10%. In field trials, similar enhancement of terbacil and chlorpropham activity was obtained on several weeds. Onions (Allium cepa L., var. Spartan Gem) in the “loop stage” were moderately tolerant and carrots (Daucus carota L., var. Royal Chantenay) were highly tolerant to chlorpropham at 4 lb/A applied in the isoparaffinic oil. Peppermint (Mentha peperita L.) and spearmint (Mentha spicata L.) were tolerant to terbacil applied in the oil at rates sufficient to give good weed control. The oil alone had no injurious effects on onions, carrots, peppermint, or spearmint. This enhancement in activity in greenhouse and field studies appeared to be due to increased penetration as shown by washing, speed of killing plants, and tracer studies. Tracer studies showed that within 2 hr after application, the isoparaffinic oil increased the penetration of chlorpropham more than eightfold in ivyleaf morningglory and more than fourfold in giant foxtail compared to a water carrier. This increase in penetration was even more striking with terbacil. After 4 hr, penetration was increased over 16 times in ivyleaf morningglory and over 18 times in giant foxtail, when applied in the oil rather than acetone. Chlorpropham and terbacil were translocated to the shoot apex of ivyleaf morningglory only when they were applied in the oil.

Excellent protection from 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) injury at twice the dose needed for weed control was obtained by dipping the roots of strawberry plants (Fragaria grandiflora Ehrh.) in a 10% slurry of activated carbon before transplanting. Protection was greater when the roots were dipped in the slurry of activated carbon than when activated carbon was applied in the transplant water. Protection was obtained from three different activated carbons. Protection from injury to varying degrees was observed when several other herbicides were used.

The adsorption of 2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine (ametryne) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) varied greatly among 34 Puerto Rican soils was studied using the agitated slurry technique. Adsorption was expressed as a distribution coefficient (Kd), which is the ratio of the amount of herbicide adsorbed to the amount in the equilibrium solution. In general, diuron was adsorbed to a greater degree than ametryne. Adsorption of ametryne was positively correlated with organic matter and silt content but negatively correlated with pH of the soil. The inclusion of soil pH in a multiple regression analysis contributed the highest increase in explanation for adsorption of ametryne. Adsorption of diuron was highly correlated with organic matter content and cation exchange capacity. A correlation was found between adsorption of diuron and content of magnesium, and soil texture. Cation exchange capacity was the only inclusion soil property which, in addition to organic matter, significantly contributed to the adsorption of diuron. Temperature appeared to have a greater effect on the adsorption of diuron than on the adsorption of ametryne. Conversely, the effect of pH on the adsorption of ametryne was significantly greater than that of diuron.

The selectivity of 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) in winter wheat (Triticum aestivum L., var. Nugaines), a resistant species, and coast fiddleneck (Amsinckia intermedia Fisch. & Mey.), a susceptible species, was concluded to be the result of a complex of interactions. Wheat was 109 times more tolerant of bromoxynil than was coast fiddleneck. More spray solution was retained by coast fiddleneck plants than by wheat. Bromoxynil penetrated more rapidly into leaves of coast fiddleneck than of wheat. However, these factors did not fully explain bromoxynil selectivity. When differential spray retention and bromoxynil penetration was accounted for, it was estimated that coast fiddleneck was 30 times more susceptible than wheat.

The herbicide 3-tert-butyl-5-chloro-6-methyluracil (terbacil) applied in an isoparaffinic oil caused, in susceptible ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.), rapid and nearly complete inhibition of photosynthesis, from which it never recovered. Photosynthesis in peppermint (Mentha peperita L.), a tolerant species, was decreased only temporarily. Terbacil was readily absorbed by leaves of both species; however, there was little or no movement out of the treated peppermint leaves. Terbacil was translocated out of the treated leaves of ivyleaf morningglory to the untreated leaves and shoot apex. It was metabolized in both species but at a higher rate in peppermint. Therefore, it appears that foliarly-applied terbacil may be bound in peppermint leaves and this, together with the higher rate of metabolism, may contribute to the tolerance of peppermint. Terbacil was readily taken up and translocated to the foliage of both species when applied to the roots. Again, it was metabolized in both plants but at a higher rate in peppermint. However, the rate of metabolism alone did not appear to be sufficient to account for peppermint tolerance to root-applied terbacil.

Germination of tumble mustard (Sisymbrium altissimum L.), tansy mustard (Descurainia pinnata (Walt.) Britton), and yellowflower pepperweed (Lepidium perfoliatum L.) is partially dependent on total degree hours of incubation (temperature above 0 C times the duration of incubation). This relation was similar under constant or alternating temperatures. Alternating temperature regimes with −20 C inhibited germination, and greatly depressed subsequent germination at optimum temperatures. Tansy mustard and yellowflower pepperweed have temperature-dependent after-ripening requirements. Germination of all three species responded similarly to osmotic stress. The relation between tumble mustard germination under osmotic or soil moisture stress is dependent on the texture of the soil substrate. A mucilaginous coating greatly aids the germination of yellowflower pepperweed seeds on the surface of media under low (0.05 to 0.2 bars) moisture tension. Germination of seeds of the three species recovered in soil samples from the field is radically different from that of freshly harvested material. The seeds acquire a dormancy which is broken irregularly under ideal conditions for germination.

The effect of 2,3,5-trichloro-4-pyridinol (pyriclor) on some photochemical reactions that bring about the formation of assimilatory power—the generation of adenosine-5′-triphosphate (ATP) and reduced nicotinamide-adenine dinucleotide phosphate (NADHP2)–at the expense of radiant energy has been determined using isolated spinach (Spinacia oleracea L., var. Viroflay) chloroplasts. The assimilation of carbon dioxide and cyclic photophosphorylation catalyzed by riboflavin-5′-phosphate (FMN) both showed inhibition at a rather high level of the pyridinol. However, oxygen evolution and non-cyclic photophosphorylation were strongly inhibited. Evidence is presented to support the conclusion that the locus of attack is the oxygen-evolving system and/or Pigment System 2 of the photosynthetic apparatus.

The possibility of an interaction between (2,4-dichlorophenoxy)acetic acid (2,4-D) and frost-injured plants of spring wheat (Triticum aestivum L., var. Manitou) was investigated. Application of 2,4-D was made either a few hours prior to the frost or at varying periods following the frost. Although there was no statistical evidence of any interaction between the frost and 2,4-D, yields of grain tended to be lowest when plants were exposed to both frost and herbicide. On the basis of results obtained, it was concluded that there is no great risk of severe damage occurring to frost-damaged spring wheat plants if they are treated with 2,4-D within a short period of being exposed to frost.

The relation of translocation and degradation to selectivity of 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) in winter wheat (Triticum aestivum L., var. Nugaines), a resistant species, and coast fiddleneck (Amsinckia intermedia Fisch. & Mey.), a susceptible species, was examined. Radioautographic and extraction analysis revealed that the label from 14C-bromoxynil was more mobile in coast fiddleneck than in wheat. Higher levels of soluble radioactivity were found in extracts of coast fiddleneck than wheat. Higher levels of insoluble label were found in tissue residues of wheat than coast fiddleneck. In both species, most of the activity remained in treated leaves. A high percentage of the soluble activity was attributed to 14C-bromoxynil in both wheat and coast fiddleneck. The evolution of 14CO2 by wheat treated with 14C-bromoxynil significantly exceeded that of coast fiddleneck. The difference in susceptibility between winter wheat and coast fiddleneck appears to be explained partly by differential translocation and degradation of bromoxynil.

In preemergence application of six different substituted urea herbicides on coriander (Coriandrum sativum L.) and tomato (Lycopersicum esculentum Mill.), the monohalogenated compounds were more effective in the destruction of the plants than their dihalogenated counterparts. The relative difference in effectiveness was much greater in the resistant coriander which appears to take up less dihalogenated than monohalogenated herbicide. In postemergence application, the dihalogenated herbicides generally were slightly more toxic than their monohalogenated counterparts.

Two phototoxic compounds, xanthotoxin (8-methoxysporalen) and bergapten (5-methoxypsoralen), were isolated from spring parsley [Cymopterus watsonii (Coult. & Rose) Jones] by thin-layer chromatography, and identified by comparison of Rf values, infrared spectra, and melting points, with pure samples. The concentration of xanthotoxin was two to four times that of bergapten in plant samples collected during the 2-month growing season. Seeds contained xanthotoxin and bergapten in equal concentrations.

Economic evaluation of Scotch thistle (Onopordium acanthium L.) infestation of grazing land in northeastern California revealed potential annual losses to ranchers approximated $10.20/A for wet meadows, $6.70/A for wheatgrass (Agropyron spp.) stands, and $3.40/A on downy brome (Bromus tectorum L.) rangelands. Annual application of 0.06 lb/A of 4-amino-3,5,6-trichloropicolinic acid (picloram) provided the most economical ($3.57/A) means of suppressing Scotch thistle. Annual application of 0.06 lb/A also introduced less picloram into the environment than less frequent application of higher rates. Application of picloram to suppress Scotch thistle limits management options and reduces potential land values.

Treatment of tobacco (Nicotiana tabacum L., var. NC-402) with 2,3,5-trichloro-4-pyridinol (pyriclor) leads to progressive disruption of chloroplast ultrastructure. Initial changes include the inception of a spherical form, swelling of the fret system, and commencement of loss of starch. More advanced changes include the complete disappearance of starch, further swelling and disorganization of the fret membrane system, followed by swelling and disruption of the membranes of the granal discs and rupture of the chloroplast envelope. The changes induced by pyriclor on chloroplast ultrastructure in tobacco are analagous to those caused by 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) on kidney bean (Phaseolus vulgaris L.) and barnyardgrass (Echinochloa crusgalli L. Beauv.). The shape and size of mitochondria were not altered by treatment with the chemical; however, there appeared to be a significant increase in the number of mitochondria present when alterations in chloroplast structure could be seen. The appearance of visual symptoms of phytotoxicity (chlorosis) correlated with the onset of disruptive changes in chloroplast ultrastructure.

A technique was developed for seeding rangelands which are too steep or too rocky to seed by current methods. Hardinggrass (Phalaris tuberosa L. var. stenoptera (Hack.) Hitchc.) and subclover (Trifolium subterraneum L.) were established by seeding immediately after spraying the resident vegetation with 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat). Tested for seeding in sod were single-disk, double-disk, and hoe-type drill openers. The double disk was best adapted to the clay soils most common in the area. A heavy-duty rangeland drill was modified with custom-made, heavy, double-disk openers and equipped with a spray system which sprays either bands or full coverage. The resulting planter will kill weeds, plant seeds, and spread fertilizer any place where a crawler tractor can pull it. Weed-free bands of 6 and 12 inches were compared with full spray coverage. No hardinggrass was established without some weed control. In only 5 of 16 tests over a 5-year period was full-spray coverage superior to the 6-inch band. The 12-inch band or full spray may be preferable on shallow soils or soils of low water-holding capacity. Spraying helped establish subclover but, unlike with hardinggrass, was not critical. Grazing or mowing during the establishment period improved stands of both hardinggrass and subclover. Prolonged weed control made paraquat superior to cultivation by giving better weed control and a firmer seedbed.

We applied 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) to quackgrass (Agropyron repens L. Beauv.) at different stages of growth and subjected these treated plants to different light regimes. After paraquat and light treatment, foliage was removed and the reduction in regrowth was measured as evidence of paraquat movement and its effect on the regenerative potential of the rhizomes. Paraquat or a toxic metabolite moved in quantity from point of leaf application. Sufficient basipetal movement occurred in both the dark and light to significantly affect regrowth. As quackgrass plants matured and developed more foliage, the effect of paraquat treatment increased (i.e., the regrowth capacity of the plants and the regenerative ability of their rhizome buds decreased). A period of darkness (24 hr) after paraquat application and before exposure of treated plants to light did not affect numbers of plants killed but did decrease rate of regrowth. Treated quackgrass foliage showed extensive paraquat injury when placed in light for 48 to 72 hr after treatment; but only parts of treated leaves were killed. Leaving treated foliage intact greatly increased the number of plants killed.

We sprayed yellow nutsedge (Cyperus esculentus L.) with 0.56, 1.12, and 2.24 kg/ha of (2,4-dichlorophenoxy)acetic acid (2,4-D) at the two and four-leaf stages in both field and growth chamber studies. Compared to non-treated plants, these rates significantly reduced shoot weight, rhizome weight, and rhizome number 12 days after application. There were no significant differences in these growth responses among the rates tested, when applied one, two, and three times at consecutive 12-day intervals. We pretreated two and four-leaf plants with 0.56, 1.12, and 2.24 kg/ha of 2,4-D immediately before foliar application of 14C-2,4-D. The increase in pretreatment rates decreased the percentage of the applied radioactivity which was absorbed and translocated. Of the radioactivity absorbed, a rather constant percentage translocated from the treated area in the different treatments. The radioactivity translocated from the application site for at least 288 hr after treatment. Less than 19% of the 14C-2,4-D applied was absorbed into the leaves 24 hr after application. Ninety-eight to 100% of the methanol-soluble radioactivity that translocated to developing leaves, rhizomes, and roots chromatographed identically to 14C-2,4-D.

Seedlings of 19 plant species were grown in soils containing 0 to 1,000 ppm of O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide (bensulide) or 0 to 100 ppm of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) to determine phytotoxicity. Standard growth curves were constructed. The concentration of bensulide required to reduce the growth of shoots 50% (GR50) ranged from 1 ppm with barnyardgrass (Echinochloa crusgalli (L.) Beauv.) to more than 1,000 ppm with carrot (Daucus carota L., var. Long Imperator). Several plant species were more sensitive to bensulide in a Hidalgo sandy loam (pH 8.1) than in other soils including a Delfina loamy fine sand (pH 6.0). The concentration of trifluralin required to reduce the growth of shoots 50% (GR50) was not markedly affected by soil texture and ranged from 0.1 ppm with German millet (Setaria italica (L.) Beauv.) to more than 100 ppm with Long Imperator carrot. The standard growth curves have been used to quantify herbicidal activities in field soils.

There is little evidence that herbicides from agronomic or industrial usage are reaching or accumulating in our water supplies in amounts to cause a pollution problem. Fish tolerance to weed killers varies with their size and species as well as with differences in the aquatic site. There may be variation to different forms of the active ingredient. Other components in a formulation may be more toxic than the herbicide itself. Therefore, the LD50 of different formulations should be determined. In addition, the manner and other circumstances involving application of a herbicide may change its toxicity to water inhabitants. Our current knowledge of the effects of herbicides on fish, plankton, and other water inhabitants indicate that harmful effects with our present herbicides, when such exist, are only temporary. Available evidence suggests there is no biological magnification problem with herbicides.