Toxicity to oats of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), monuron (3-(p-chlorophenyl)-1,1-dimethylurea), and fenuron (3-phenyl-1,1-dimethylurea), exposed to sunlight on soil surface for 25 days was significantly decreased even when surface soil temperatures did not exceed 120 F. Only atrazine and monuron exhibited significantly less phytotoxicity after 60 days exposure than after 25 days. Simazine phytotoxicity also was significantly reduced when held on soil in the dark for 60 days. With the exception of fenuron, there was no difference between treatments within compounds when soil temperatures reached maximums as high as 180 F. Under these conditions, phytotoxicity of the herbicides was reduced 65 to 97 percent by all exposures.

The various descriptive names used in the literature for each bulb type of wild garlic are reviewed and a suggested standard system of bulb nomenclature is presented. The life cycle of the species is briefly reviewed, with emphasis on cycles between plant and bulb types. The morphology, anatomy, ontogeny and physiology of the common bulb types are compared.

Combinations of 3-chloro-2-methyl-p-valerotoluidide (solan) with 1,1′-dimethyl-4,4′-dipyridylium cation (paraquat) were used postemergence in transplanted tomatoes (Lycopersicon esculentum Mill.). Addition of .05 lb/A of paraquat to 2 or 4 lb/A of solan resulted in more effective control of crabgrass (Digitaria sanguinalis (L.) Scop.) than did doubling the rate of solan. The combinations were synergistic on crabgrass but only additive or more often antagonistic on tomato plants. The herbicides dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA) and sodium 2,4-dichlorophenoxyethyl sulfate (sesone) were applied for preemergence weed control in strawberry beds. Velvetleaf (Abutilon theophrasti Medic.) was resistant to both DCPA and to sesone, but was quite susceptible to the combination. Combinations of 4,6-dinitro-o-sec-butylphenol (DNBP) with 2-methoxy-4,6-bis(ethylamino)-s-triazine (simetone) were highly synergistic on tomato plants. This synergism was more pronounced at low rates of herbicides.

Preemergence applications of DCPA (dimethyl 2,3,5,6-tetrachloroterephthalate) controlled germinating seedlings of largeseed dodder (Cuscuta indecora Choisy) in alfalfa, and the control continued throughout the season. Applications of DCPA were necessary prior to germination of dodder seed. Under California conditions, applications of DCPA made during early winter (December) provided early season control but not satisfactory control throughout the season as was accomplished with the March treatments. Autoradiographic studies showed only limited movement of tracer in alfalfa plants.

Mugwort (Artemisia vulgaris L.) was controlled by soil applications of potassium azide at 100 lb/A and equimolecular amounts of sodium azide in greenhouse studies. Rooted Artemisia plants exposed to exponential concentration ranges of these herbicides in ¼ strength Knops nutrient solution showed lethal effects at 10-3 M of either the potassium or sodium azide. Vapors of the potassium and sodium azides caused leaf injury at relatively low rates. Bioassays indicated dissipation of 100 lb/A of the azides in the soil in 6 weeks under greenhouse conditions.

Root moisture extraction profiles varied from 20 square feet for Kochia scoparia (L.) Schrad, (kochia to 44 square feet for Xanthium pennsylvanicum Wallr. (cocklebur). Weeds within the extremes with increasing root moisture extraction profiles were Eragrostis pectinacea (Michx) Ness (tufted lovegrass), Solanum rostratum Dunal. (buffalobur), Digitaria sanguinalis (L.) Scop. (large crabgrass), Tribulus terrestris L. (puncturevine), Salsola kali L., var. tenuifolia Tausch (Russian thistle), Amaranthus palmeri S. Wats. (Palmer amaranth) and sorghum.

Canada thistle [Cirsium arvense (L.) Scop.] infestations were treated with 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) at 10 rates ranging from 5 to 160 lb/A. Depths to which monuron leached were determined annually by bioassays with flax, peas and wheat. Toxicity at all rates continued for 3 years. The low sand, high clay, and high organic matter contents of this soil combined with cool or dry climatic conditions inhibited leaching and prolonged the toxicity of monuron.

In greenhouse tests, temperature, humidity, drought stress, and concentration of surfactant influenced the foliar activity of spray mixtures containing a dodecyl ether of polyethylene glycol (Surfactant WK) and 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (diuron) or 3-(3,4-dichlorophenyl)-1-methoxy-1-methyl urea (linuron). In comparisons with other commonly used surfactants, Surfactant WK gave a superior performance when used in conjunction with diuron, linuron, and 5-bromo-3-sec-butyl-6-methyl uracil (bromacil). Increased water solubility of these herbicides in the presence of surfactant is only one factor among many involved in the enhanced activity of such combinations. Surfactant WK facilitated the deposition of high concentrations of linuron on leaf surfaces of Johnsongrass. Once a gradient was established, subsequent rapid movement of the herbicide into the leaf was noted.

The effect of temperature and relative humidity on root and foliar uptake of C14-labeled atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) in quackgrass (Agropyron repens (L.) Beauv.) was studied in a controlled environment growth chamber. Uptake and translocation of root-fed atrazine increased as temperature increased. Greater uptake and translocation of root-fed atrazine occurred under low relative humidity than under high relative humidity. Slightly greater uptake and translocation of foliar-applied atrazine occurred as temperature was increased from 60 to 80 F.

Lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and white mustard (Brassica hirta L.) were highly susceptible to 2-methyl-4-chlorophenoxyacetic acid (MCPA) regardless of the pretreatment light exposure to which they were subjected. These broadleaved weeds were slightly more susceptible to MCPA applied after a prolonged period of darkness. Neither total carbohydrate, reducing sugar, protein, nor amino acid contents at the time of spraying were associated with the susceptibility of mustard plants to MCPA. Floral bud development on Canada thistle was greatly reduced by MCPA applied at any time of the day to plants 9 and 12 inches tall and was prevented on plants 3 and 6 inches tall. The susceptibility of broadleaved annual weeds and Canada thistle to MCPA was not affected by variations in temperature and humidity at time of spraying.

In greenhouse experiments high levels of phosphorus tended to suppress growth of soybeans, oats, and foxtail in the presence of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) as compared to controls containing no simazine. However, this relationship was not significant, varying with the soil used in the experiment. Emergence of the seedling was delayed and the concentration of ions in solution increased as phosphorus applications were increased. Mineral uptake by soybean shoots was unaffected by phosphorus or simazine alone, but markedly disrupted in the presence of both simazine and phosphorus. Changes in mineral uptake were typical of effects produced by phosphorus toxicity, indicating that simazine reduced the amount of phosphorus required to produce salt injury.

Anionic and cationic surfactants differentially enhanced the phytotoxicities of four herbicides to corn and soybeans in relation to variations in their structure. Thirteen ionic and two related nonionic surfactants were studied in sprays containing water-soluble forms of 2,2-dichloropropionic acid [dalapon], 2,4-dichlorophenoxyacetic acid [2,4-D], 4,6-dinitro-o-sec-butylphenol [DNBP], and 3-amino-1,2,4-triazole [amitrole]. Effects of surfactant structure, type, and concentration on two other spray properties—surface tension and specific conductivity—were measured at three pH conditions.

Appreciable enhancement of herbicide toxicities occurred only at the highest concentration, 1.0 g per 100 ml (1.0 percent). With straight-chain isomers of an alkylbenzenesulfonate (ABS) anionic surfactant, enhancement of all herbicides increased as the position of the benzene ring was moved to the mid-chain (C5 and C6) carbons of an n-dodecyl alkyl group. DNBP toxicity to both species and surfactant toxicities to soybeans were increased progressively in separate odd- and even-carbon series, i.e. a C1,3,5-series and a C2,4,6-series. Other ABS variations which provided marked enhancement were use of a highly-branched dodecyl alkyl and substitution of an ester oxygen atom for the benzene ring. Among ethoxylated alkylamine cationic surfactants, variations in alkyl structure affected differentially the toxicities of the various herbicides at alkaline, neutral, and acid pH. Surfactants caused marked modification of physical-chemical properties of sprays in relation to their structure and concentration. However, no one of the properties studied could be correlated consistently with the herbicidal effectiveness of a spray. Results suggested that spray performance of herbicide formulations can be improved by using more effective surfactants to achieve other desired formulation characteristics. The increased toxicity of 2,4-D in certain alkaline sprays also suggested that the conditions necessary for absorption of 2,4-D should be examined more critically.

Structural characteristics of surfactants and a herbicide were incorporated in the same molecule by forming long-chain alkylamine salts of 2,4-dichlorophenoxyacetic acid [2,4-D]. In water sprays, all of the 2,4-D salts showed surface activities characteristic of surfactants. The application rate of 2,4-D was held constant at 1/16 lb ae/A; salt concentration was varied by varying spray volume. Seventeen salts were herbicidally active on soybeans at a high concentration (1/16 lb ae in 10 gpa of spray) and a few were also active at a lower concentration (1/16 lb ae in 40 gpa). The remaining thirteen salts were relatively inactive in water. Structural features associated with water-active salts of 2,4-D were those which contribute to hydrophilic characteristics of surfactants. Lipophilic structural features contributed to inactivity in water.

The 2,4-D toxicity of fourteen water-active and water-inactive salts of 2,4-D was maximally and equally elicited in one or more of six water and oil spray systems. Differential activities of the salts permitted their classification into six distinct classes—three hydrophilic and three lipophilic. No one of five solution properties—surface tension, interfacial tension, turbidity, specific conductivity, or pH—could be correlated with herbicidal toxicity of a spray. However, a combination of three properties—interfacial tension, turbidity, and specific conductivity—provided some indication of the relative hydrophilic or lipophilic character of a salt and of the 2,4-D toxicity in different sprays. Data suggested that herbicides move into plants by two distinct pathways—one hydrophilic and the other lipophilic.

Castorbeans (Ricinus communis L.) are extremely tolerant of the rotary hoe. Its timely use plus cultivation gave effective weed control in castorbeans. The preemergence herbicides, used either alone or in combination, that appeared most promising for selective control of weeds in castorbeans were: 2-chloro-N,N-diallylacetamide (CDAA), dimethyl-2,3,5,6-tetrachloroterephthalic acid (DCPA), ethyl N,N-dipropylthiolcarbamate (EPTC), N-1-naphthylphthalamic acid (NPA), 2,6-dinitro-N,N-dipropyl-alpha, alpha, alpha-trifluoro-p-toluidine (trifluralin), and propyl dipropylthiolcarbamate (R-1607). The most dependable weed control practice in castorbeans was the use of preemergence herbicides in combination with rotary hoeings plus cultivation.

Soybeans treated preemergence with carboxyl-labeled C14 amiben (3-amino-2,5-dichlorobenzoic acid) were harvested at 7-day intervals. The C14 activity per gram of dry plant matter decreased with later harvest dates but the activity per plant increased over the period. The cotyledons had considerable radioactivity. Both rates contained the same amount of C14 amiben but the soybeans exposed to 6 lb/A contained a significantly higher C14 count than did those exposed to 3 lb/A. All of the identifiable C14 components were amiben.

Most of the activity in soybeans from seed imbibed with C14 amiben remained in the cotyledons. That which did translocate was evenly distributed. Most (98.1%) of the radioactivity in plants grown in treated nutrient solution remained in the roots. Translocated C14 amiben appeared about 8 days after exposure and was evenly distributed in the top of the plant. Plant-respired CO2 had no radioactivity present.

An apparatus for trapping the vapors of ethyl N,N-dipropylthiolcarbamate (EPTC) and other herbicides froms soils under field conditions is described. The herbicide vapors were collected in cooled traps along with ice crystals, identified by gas chromatography and determined quantitatively. The amount of EPTC lost and trapped in 30 minutes ranged from 22 to 38 % of that applied to the surface of six different types of wet soils. The amount lost from dry soils was much less than from moist soils. Letting the surface of six different types of wet soils. The amount lost from dry soils was much less than from moist soils. Letting the surface of freshly worked moist soil dry out to depth of ½ inch before spraying with EPTC, greatly reduced the loss by vaporization. Immediate incorporation prevented any loss of EPTC from dry soil and greatly reduced the loss from moist soils. After spraying EPTC on dry soil, sprinkling with small amounts of water increased the loss. Comparison of several thiolcarbamate herbicides showed that n-propyl N,N-di-n-propylthiolcarbamate (R-1607) and n-propyl ethyl-n-butylthiolcarbamate (PEBC) were lost by vaporization at a slower rate than EPTC, and S-ethyl hexahydro-1-H-azepine-1-carbothioate (R-4572) was lost at a much slower rate than the other herbicides tested.

The disappearance of EPTC (ethyl N,N-di-n-propylthiolcarbamate) from soils was studied by steam distilling the remaining EPTC from the soil samples and analyzing the distillates. The most important factor affecting the loss of EPTC from soil was the amount of moisture in the soil. During the first 15 minutes after spraying on the soil surface, 20% of the applied EPTC disappeared from dry soil, 27% from moist soil and 44% from wet soil. The loss was 23, 49, and 69% after one day and 44, 68, and 90% after six days on dry, moist, and wet soils, respectively. No significant loss of EPTC occurred the first few hours after applying granular EPTC to dry soil or soil containing 4 to 6% moisture, but on soil at 15% moisture the loss from granules was 60% in two hours. There appeared to be a critical moisture level for each soil, above which large losses of EPTC occurred after application to the surface or after shallow incorporation. Depth of incorporation was the second most important factor in EPTC loss from soils. Incorporation to at least 2 to 3 inches was necessary to prevent large losses of EPTC when light rain or sprinkler irrigation followed treatment. EPTC was lost at a faster rate on sunny days than cloudy days. Increasing the temperature from 32 to 60 F, increased the rate of EPTC vaporization from moist soil but had no effect on the loss from dry soil.

The sensitivity of giant duckweed (Spirodela polyrhyza (L.) Schleid), common duckweed (Lemna minor L.), Wolffiella floridana (Smith) Thomp., azolla (Azolla caroliniana Willd.), and watermeal (Wolffia columbiana Karst.) to diquat (6, 7-dihydrodipyrido [1,2-a:2’,1′-c] pyrazidiinium salt) and paraquat (1,1′-dimethyl-4,4′-bipyridinium salt) was in that order (most to least sensitive). The rapidity of chlorosis in giant duckweed was directly related to the light intensity. The light quality having the most effect on the activity of diquat and paraquat on duckweed was red (600+ millimicrons), and green (510–560 millimicrons) had the least effect.

Downy brome (Bromus tectorum L.) control by 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat) was increased from 12% without surfactant to 73 to 94% with 17 of 22 surfactants. Paraquat toxicity was greatest at 0.06 and 0.12% surfactant concentrations and decreased at higher concentrations. The less effective surfactants were less water-soluble and more lipophilic than related, more effective ones.

S-propyl-1-C14-N,N-ethyl, n-butylthiolcarbamate (PEBC-C14) residue was generally higher in the roots than in the corresponding above-ground portions, and also greater in plants receiving a higher rate of treatment The concentration decreased as a function of time after treatment. The average values of PEBC residue in the fresh foliage, during the first two weeks after receiving a lay-by treatment at blooming stage, were 0.098, 0.465 and 0.860 ppm for 1, 4 and 8 lb/A rates respectively. No PEBC residue was found in fruits from plants receiving any rate of treatment at blooming stage. A small amount of the residue was found in fruits from plants treated at early fruiting stage and this decreased rapidly to zero level after four or five weeks.

The metabolic breakdown of PEBC in the tomato foliage and fruits is a first-order process. The rate constant for PEBC breakdown seemed to depend upon the tissue as well as the stage of growth.