Directed applications of low rates of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), disodium methanearsonate (DSMA), monosodium methanearsonate (MSMA), 1,1′-dimethyl-4,4′-bipyridinium salts (paraquat), and 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) controlled annual weeds in irrigated cotton (Gossypium hirsutum L.). Although the first applications of most herbicides caused temporary, localized foliage chlorosis or burning, cotton yields, fiber properties, and boll components were not affected. Early applications of DSMA followed by diuron selectively controlled annual weeds. When a herbicide was applied before planting, fewer postemergence applications were needed for weed control.

We characterized soil and vegetation assemblages, many of which are infested with medusahead (Taeniatherum asperum (Sim.) Nevski), on the margin of the Great Basin. Interpretations of these assemblages provide an index of the validity of the basic environmental unit of this ecosystem which can be manipulated through weed control and revegetation techniques. Vertisol (churning clay soils) sites with sparse native plant communities are more susceptible to medusahead invasion than more complex low sagebrush (Artemisia arbuscula Nutt.) or low sagebrush-woodland communities on related clay soils. If the more complex communities are degraded to a low seral state, medusahead can invade and occupy the site. Wet meadows and burned coniferous forest sites at high elevations were the only sites where medusahead occurred on soils with textures other than clay. Big sagebrush (Artemisia tridentata Nutt.) communities on medium to coarse textured soils were very resistant to medusahead invasion. The restriction of medusahead to certain sites controls the mechanism of invasion and interacts with the breeding system of the species to influence its evolution.

The phytotoxicity of 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) usually decreased as the stage of growth of five weed species at treatment increased. Giant foxtail (Setaria faberii Herrm.), velvetleaf (Abutilon theophrasti Medic.), and the cotyledonary stage of cocklebur (Xanthium pensylvanicum Wallr.) were most resistant to the herbicide. Ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.) and jimsonweed (Datura stramonium L.) were more susceptible to chloroxuron. Soybean (Glycine max (L.) Merr.) seemed less susceptible at the cotyledonary stage than at later stages. Phytotoxicity on both weeds and soybeans was increased by increased temperature and relative humidity following chloroxuron application. The phytotoxicity of chloroxuron also was increased by simulated rainfall in greenhouse studies.

The uptake of herbicides by soybean (Glycine max (L.) Merr.) seed from 14C-labeled aqueous solutions of 3-amino-2,5-dichlorobenzoic acid (amiben), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), S-ethyl dipropylthiocarbamate (EPTC), and isopropyl m-chlorocarbanilate (chlorpropham) was determined by measuring reduction in the concentration of the herbicides in the soaking solution. There was a direct proportional relationship between uptake and concentration. Raising the temperature from 10 to 30 C increased uptake of herbicides. The greatest increase occurred from 10 to 20 C. After 48 hr at 30 C, 39% of the amiben, 61% of the atrazine, 65% of the EPTC, 83% of the linuron, and 92% of the chlorpropham in the original solution was absorbed by the seed. Uptake rates were similar in living and dead seed. Uptake was reversible with amiben but not with chlorpropham. Absorption of herbicides could not be associated with absorption of water except during the first few hours when the seed were rapidly imbibing water. Ratios of seed to solution herbicide concentrations all exceeded 1:1 after 48 hr and with chlorpropham, reached 68:1. The uptake of herbicides by seed was largely a physical process that required seed hydration, but herbicide uptake continued after water uptake ceased.

Seeds of Pennsylvania smartweed (Polygonum pennsylvanicum L.), quackgrass (Agropyron repens L. Beauv.), yellow foxtail (Setaria lutescens L. Beauv.), and wild mustard (Brassica kaber (DC) L. C. Wheeler) were studied to determine if histochemical differences existed in seeds of dormant and non-dormant weed species. The hulls (seedcoat) of yellow foxtail and seedcoats of wild mustard and quackgrass had distinct inhibitory effects on germination. Endosperm tissue in wild mustard and Pennsylvania smartweed also inhibited embryo growth in these species. Results obtained from specific staining techniques on seed sections 10μ thick for identification and determination of distribution of proteins, lipids, carbohydrates, and lignin in dormant and germinating seeds suggested that possible mechanisms of seed dormancy are: (a) lower protein content in seed tissues of wild mustard; (b) higher lignification in hull of foxtail and endosperm of Pennsylvania smartweed; (c) lower sterol content in embryo of wild mustard and Pennsylvania smartweed; (d) high cellulose content in hull of foxtail and endosperm of Pennsylvania smartweed. Excised embryos from dormant seeds of Pennsylvania smartweed showed a measurable amount of growth in White's standard agarnutrient. Germinating embryos of wild mustard and quackgrass were larger than those in dormant seeds; therefore, immaturity of embryos might contribute to dormancy in these species.

A somewhat modified version of Lambert's quantitative treatment of the influence of soil-moisture content on herbicidal activity has been applied to 4-amino-3,5,6-trichloropicolinic acid (picloram) behavior in soil. The bioactivity of picloram decreased as the soil-moisture content was increased. This was due to the effect of varying soil-moisture levels on the concentration of picloram in the soil-water phase.

Field studies of seasonal sprouting of wild garlic (Allium vineale L.) bulbs showed that all the soft offset, aerial, and central bulbs sprouted, but only 20 to 34% of the hardshell bulbs sprouted after a short after-ripening period. Each fall, a percentage of the remaining hardshell bulbs sprouted, but after 4 years 16% of the hardshell bulbs were still dormant. Embryonic shoots of all bulb types sprouted when excised following the after-ripening period. In addition to a short after-ripening period, hardshell bulbs had a prolonged dormancy due to some mechanism which resides in, or was controlled by, the tissue surrounding the embryonic shoot.

Soybean (Glycine max (L.) Merr., var. Chippewa 64) plants were grown in culture solutions containing 14C ring-labeled 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine). Culture solution temperatures were varied but ambient temperature about the shoots was constant. The amount of atrazine absorbed increased with increases in herbicide concentration, absorption time, and root temperature. Root temperature had more influence on atrazine accumulation in stems and leaves than in roots. Transpiration rates of atrazine-treated plants were reduced at least 50%.

Field-harvested johnsongrass (Sorghum halepense (L.) Pers.) rhizomes were assayed for bud dormancy and growth potential under a number of experimental conditions. Natural dormancy was not detected in single-node rhizome pieces harvested at any time of the year. Shoot growth rates were highly variable. Kinetin, benzyl adenine, gibberellic acid, and 2-chloroethylphosphonic acid were ineffective in enhancing germination or normalizing shoot growth. Scale leaves of rhizomes had no effect on bud growth. Rhizome buds were strongly influenced by apical dominance and emerged shoots partially suppressed germination of adjacent buds. The optimum temperature for bud germination and shoot growth was approximately 30 C. Bud germination was suppressed at 15 C. Johnsongrass rhizomes failed to exhibit cold hardiness at any time in their life cycle.

The metabolic fate of root-applied, carbonyl-labeled, 14C-3-(3-chloro-4-bromophenyl)-1-methoxy-1-methylurea (hereinafter referred to as chlorbromuron) was investigated in tolerant corn (Zea mays L., var. N.J. 9) and susceptible cucumber (Cucurbita sativus L., var. Marketer) in a time-course study. The major metabolite found in corn shoots and roots was the nonphytotoxic 3-(3-chloro-4-bromophenyl)-1-methoxyurea. Evidence of “binding” was found in both shoots and roots of corn. No evidence was found for the metabolism of chlorbromuron in cucumber; however, some binding occurred in both shoots and roots.

Total foliar fatty acid and hydrocarbon content of sicklepod (Cassia obtusifolia L.) treated with 0, 0.14, 0.28, 0.56, 1.12, 2.24, or 4.48 kg/ha S-ethyl dipropylthiocarbamate (EPTC) was measured by gas-liquid chromatography. Total leaflet fatty acid content increased at sublethal rates of the herbicide, but qualitative composition of the fatty acids was not affected. Percent of long chain alkane (≥ C28) content decreased as EPTC application rates increased. Palmitic (23.9%), stearic (9.1%), oleic (3.8%), linoleic (13.6%), and linolenic (33.2%) acids accounted for 83.6% of the total leaflet fatty acid content of sicklepod. Leaflet cuticle thickness of upper and lower epidermal layers decreased 15 and 20%, respectively, as herbicide concentration increased.

The growth of soybean (Glycine max (L.) Merr.) seedlings was retarded when treated with either methyl 3-amino-2,5-dichlorobenzoate (amiben methyl ester) or α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) when compared with soybeans treated with either 3-[-p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) or 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea linuron. Seedling growth of soybeans also was retarded when treated with amiben methyl ester alone or applied in combination with O,O-diethyl S[2-(ethylthio)ethyl] phosphorodithioate (disulfoton). Insecticides did not influence growth of soybeans. Linuron applied in combination with O,O-diethyl S-[(ethyl-thio)methyl] phosphorodithioate (phorate). or methyl-N-[(methylcarbamoyl)oxy] thioacetimidate (methomyl) and amiben ester applied in combination with phorate produced significantly lower seedling vigor during only 1 year than when each pesticide was applied alone. Soybean stands were significantly lower only in 1 year when linuron was applied in combination with methomyl. None of the pesticides applied alone or in combination caused significant differences in date of maturity, lodging, seed yield, seed size, or seed quality during either year.

Sixty percent of the roots of sugarbeets (Beta vulgaris L.) at harvest were aberrant in the zone of the hypocotyledonary neck when 0.84 kg/ha of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) was sprayed primarily on the hypocotyledonary tissues of seedlings in the 10 to 12-leaf stage, compared to 7% when soil surrounded most of the hypocotyledonary tissues at the time of application. Trifluralin did not reduce the yield of roots or kilograms of sucrose per hectare in either treatment. Sucrose content and purity were lower, and total nitrogen was more than twice as high in sections of neck and root tissues where the aberrations were the most severe as compared to normal sections of neck and root tissues from the untreated plots. In the greenhouse, trifluralin inhibited the growth of primary and lateral roots in sugarbeet seedlings.

The uptake and release of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) by green sunfish (Lepomis cyanellus Raf.) were measured during a 3-week exposure to either non-labeled or symmetrically ring-labeled 14C-simazine. Exposure was by feeding (3 and 10 mg/kg body wt) or bath (1 and 3 ppm). To determine the retention of simazine, treated fish remaining after exposure and sampling were placed in fresh water for 4 weeks. This water was changed weekly. Fish in the bath absorb simazine in amounts directly proportional to the concentration in the water: i.e., 0.95 and 2.29 ppm total residue after 3 weeks exposure to 1.0 and 3.0 ppm, respectively. Little or no simazine was found in feed-exposed fish 72 hr after feeding. Almost all of the residue was in the viscera. No simazine residue was detected in fish from the water bath exposure after they had been in fresh water 7 days.

Interactions between carbamate and growth regulator herbicides were antagonistic both in whole plants and in plant segments. When combinations of isopropyl m-chlorocarbanilate (chlorpropham) and (2,4-dichlorophenoxy)acetic acid (2,4-D) were applied to the foliage of either redroot pigweed (Amaranthus retroflexus L.) or pale smartweed (Polygonum lapathifolium L.), the severe twisting effects of 2,4-D were greatly reduced. This interaction did not involve differential movement or metabolism of either herbicide. The induced elongation of soybean hypocotyl sections by the three growth regulators 2,4-D, 3,6-dichloro-o-anisic acid (dicamba), and 4-amino-3,5,6-trichloropicolinic acid (picloram) was inhibited in the presence of either chlorpropham or S-ethyl dipropylthiocarbamate (EPTC). Similarly, curvature tests using soybean (Glycine max (L.) Merr.) hypocotyl sections showed the curvature induced by the growth regulators to be almost completely eliminated by the presence of the carbamates.

Total nonstructural carbohydrate (hereinafter referred to as TNC) storage in roots and utilization of TNC by yellow rocket (Barbarea vulgaris R. Br.), white cockle (Lychnis alba Mill.), and hoary alyssum (Berteroa incana (L.) DC) was studied through a 1-year life cycle in plants seeded July 8, July 22, and August 5, 1966. For yellow rocket, TNC storage was most rapid during September and reached maximum levels by November 2. Younger plants stored TNC more efficiently than did older plants, but total grams of TNC per plant were greater for older plants than for younger plants. No plants bolted during the seeding year. Rapid declines in TNC of the roots began in late March, and minimum TNC levels coincided with the completion of flowering in mid-June for all plants the year after seeding. For white cockle, TNC storage was most rapid during September and early October, and reached maximum levels for all plants by November 2. There was no apparent winter injury to any of the plants. Total growth in 1967 was greatest for plants seeded July 8 and least for plants seeded August 5. Flowering began June 2 and seed were mature June 29. Adventitious buds were present on the roots of all plants on all sampling dates from September 7, 1966, through July 7, 1967. Minimum levels of TNC during spring growth were reached in mid-June. For hoary alyssum, TNC storage was most rapid during late September and October and reached maximum levels by the middle of November. TNC levels were higher in plants seeded July 22 or August 5 than in those seeded July 8. Plants seeded July 8 were flowering profusely by the middle of September, those seeded July 22 were flowering October 6, but those seeded August 5 did not flower in the seeding year. In 1967, all plants were in full bloom May 26. Minimum TNC levels were reached at full bloom and there was no accumulation of TNC as of July 7.

Cotton (Gossypium hirsutum L.) grown at two locations in Alabama from 1966 to 1968 produced maximum yields when kept free of annual weeds for approximately 8 weeks after emergence. Weed control for longer periods failed to increase yields. When initial weed control measures were delayed until 6 to 7 weeks after emergence at one location and 4 to 5 weeks at the other location, cotton was not injured. Prolonged weed competition past the critical periods usually resulted in drastic cotton yield reductions. Plant height and stem diameter of cotton were reduced by some of the weed competition treatments.

We measured some of the more important biologic and microclimatic parameters of the functional environment of downy brome (Bromus tectorum L.) communities during the establishment period of seedlings of intermediate wheatgrass (Agropyron intermedium (Host) Beauv., var. Amur). These measurements were made in relation to weed control and seeding treatments. Weed growth and establishment of replacement vegetation were directly related to available soil moisture and favorable temperatures in the immediate environment of growing plants. Lack of available soil moisture during critical periods of the growing season was the major deterrent to seeding success. The limited precipitation stored as soil moisture was available to perennial grass seedlings where weeds were controlled. Without weed control, growth of downy brome preempted the effective precipitation, and moisture became limiting for growth of perennial grass seedlings. Seeding in furrows, along with weed control, further improved moisture conditions for the seedlings. Also, use of furrows enhanced seedling growth by lowering maximum air and soil temperatures in the seedlings' immediate environment.

In the greenhouse, we examined approximately 2,700 strains of soybeans [Glycine max (L.) Merr.] for response to 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), a herbicide which inhibits photosynthesis. Duration of survival when grown in soil containing 0.84 kg/ha was the initial selection criterion. Strains thus selected as most tolerant and most susceptible were grown then for 3 to 3 ½ weeks in soil containing 0.45 kg/ha of atrazine. The dry weight of shoots expressed as a percentage of each strain's own untreated check was used to measure the strains' tolerance of atrazine. Tolerance, thus measured, generally increased as seed size increased. Regression analysis indicated that 80% of the variation in response was attributable to variation in seed size. We suggest the possibility of minimizing soybean injury from atrazine (and perhaps other herbicides) by planting large seed.

We applied (2,4-dichlorophenoxy)acetic acid (2,4-D), (2, 4,5-trichlorophenoxy)acetic acid (2,4,5-T), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) alone and in various combinations by aircraft on arborescent species in Texas and Puerto Rico. Paraquat defoliated trees rapidly but did not give long-term control. Picloram defoliated a greater number of species than the other herbicides and defoliation extended over a longer period. No treatment killed all trees in the mixed forest or prevented regrowth and secondary succession for a period of more than 1 year. Higher herbicide rates were necessary to defoliate woody plants in tropical Puerto Rico than in subtropical Texas.