The extent of adsorption of five C14-labeled s-triazines, 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine), 2-methoxy-4,6-bis(isopropylamino)-s-triazine (prometone), and 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne) from aqueous solutions by soil constituents was expressed as a distribution coefficient (Kd), which is the ratio of the amount of herbicide adsorbed to the amount in the equilibrium solution. The Kd value for a given s-triazine and exchanger remained relatively constant over a range of concentrations. The adsorption reaction was essentially at equilibrium within 1 hour. Increasing the temperature and pH resulted in decreased adsorption of simazine and atrazine. The order of increasing adsorption of these compounds by soils was propazine, atrazine, simazine, prometone and prometryne. Increased amounts of organic matter and/or clay in a soil generally were associated with increased adsorption of these s-triazines. No adsorption of simazine or atrazine was detected with kaolinite. Putnam clay, illite, and montmorillonite were increasingly adsorptive in that order. The organic materials were generally much more adsorptive than the clays. The adsorption reaction was reversible by increasing temperatures, water elution, and elution with various organic solvents. Fifty percent ethanol plus heat was very effective in eluting the chloro-s-triazines from soil.

These herbicides for vegetables in three desert areas managed under furrow irrigation exhibited extreme variability between locations in herbicide response and crop toxicity. Some treatments provided a reasonable compromise between weed control and crop injury at any one location, none met this requirement at each location. Soil-type, soil moisture at time of herbicide application, and interaction of crops and environment probably contributed to the observed variability.

Studies in New Mexico showed basal and stump applications of ester and oil-soluble amine formulations of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) to be effective for control of saltcedar (Tamarix pentandra Pall.). Trees with trunks 2 inches or larger in diameter were harder to kill than smaller trees and retreatment was often needed. Spraying the lower 2 feet was no more effective than spraying the lower foot. Cutting the larger trees and spraying the stump increased effectiveness.

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.

In 1:1 slurry, adsorption of 2-chloro-4,6-bis (ethylamino)-s-triazine (simazine) by acid soils from saturated solution varied from 13 to 90%. Percent of adsorption from more dilute solutions was approximately that from the saturated solution. The adsorption of simazine by 18 soils was not correlated significantly with soil pH, but was correlated significantly with percent clay and highly significantly with organic matter and titratable acidity. Simazine was considered to be adsorbed by soils by proton association. Using titratable acidity as a measure of H-soil, equilibrium constants were calculated which did not vary greatly as a result of changes in acidity up to pH 8.5, or as a result of concentration of simazine in the added solution. Leon, the most adsorptive of the tested soils, gave values for the equilibrium constant that were somewhat higher than for four other soils. Simazine penetrated more deeply into limed soil than into unlimed soil. Liming reduced the decomposition of simazine as did intermittent drying. Recovery decreased with time.

Experiments of two types were conducted. (1) Weeds were allowed to grow for different periods after planting sugar beets; they were then removed and the beets hand-weeded until harvest. (2) Sugar beets were hand-weeded for different periods after planting; then no further weeding was done. Weed competition reduced beet yields up to 94%. Weeds that emerged soon after beet planting reduced yields the most, but they exerted little yield-reducing competition until later than 12 weeks after planting the beets (9 weeks after beet emergence). Full-season weed control resulted when beets were hand-weeded for 10 to 12 weeks after planting. Weeds that emerged later were controlled by crop competition.

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.

During a 2-year study corn exhibited relatively good tolerance to flaming at a speed of 4 mph. Soybeans were more susceptible to injury by flaming at early growth stages than was corn. For weed control conventional cultivation and preemergence herbicides were superior to flaming. Damage to crop or weeds was influenced by morphology of the plant, size of plant, adjustment of equipment, number of flamings, and speed or length of exposure.

This study suggests that flame cultivation would not be very competitive in areas where preemergence herbicides and conventional cultivation give satisfactory control of weeds. Although cost of gas would be about equal to cost of herbicide, cost of flame cultivation equipment is about five times greater, and flame cultivation would require 2 to 4 more trips over the field. Flame cultivation may have more potential in the drier areas where preemergence herbicides have been less effective.

A Streptomyces, apparently S. viridochromogenes, was isolated from Louisiana crop areas where seven chlorinated herbicides had been used in weed control. It liberated no chloride when grown in a liquid medium containing 100 ppm of any of these seven herbicides. With a cucumber root bioassay, detoxification of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), 2,3,6-trichlorophenylacetic acid (fenac), 2,2-dichloropropionic acid (dalapon) was observed, but little detoxification was shown with 2-chloro-N,N-diallylacetamide (CDAA), isopropyl N-(3-chlorophenyl)carbamate (CIPC), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Manometric studies with 2,4-D, 2,4,5-T, and silvex showed the streptomycete was capable of adapting to the compounds after a short period, but not to 2,4-dichlorophenol, a proposed intermediate of 2,4-D metabolism. The organism did not alter the ring structure of the aromatic herbicides, and 2,4-D and 2,4-dichlorophenol showed identical absorption curves with the spectrophotometer used.

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.

(Arbutus menziesii Pursh.) trees in the field (15–20 cm diameter) xyacetic acid (2,4-D*) and 2,4-5-trichlorophenoxyacetic acid (2,4,5-T*) in blue oak (Quercus douglasii H. & A.) seedlings occurred following application of these herbicides to cuts made through the bark into the wood of stems. Downward transport was limited. C14-labeled 3-amino-1,2,4-triazole (amitrole*), maleic hydrazide (MH*), urea*, and P32-labeled phosphate translocated extensively into the roots as well as upward into the shoots. High humidity had little effect on translocation of 2,4-D* and 2,4,5-T* into the roots, but had marked effect on translocation of amitrole*, MH*, and urea*. The addition of herbicidal amounts of unlabeled 2,4-D or 2,4,5-T reduced translocation of labeled compounds into the roots. Unlabeled 4-amino-3,5,6-trichloropicolinic acid (picloram) or 2,4-D applied to cuts prevented translocation into the roots of all but traces of MH* applied to the same cuts. Treatment of blue oak or madrone (Arbutus menziesii Pursh.) trees in the field (15–20 cm diameter) with herbicidal doses of 2,4-D or picloram largely inhibited the downward movement of P32O4 applied to the same cuts at all stages of growth; such interference was less pronounced in madrone than in blue oak.

The phytotoxicities of three phenylurea herbicides applied annually to cotton at rates used for selective weed control were studied in irrigated soils of the southwestern United States. Yields of seed cotton were generally not affected by annual applications of 3-(p-chlorophenyl-1)-1,1-dimethylurea (monuron) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). Annual applications of 3-phenyl-1,1-dimethylurea (fenuron) often reduced seed cotton yields. Mild chlorosis of foliage of cotton seedlings was occasionally observed when monuron was used annually. Although diuron affected the growth of oats and barley 6 to 12 months after application, it caused no adverse effect on cotton seedlings. Monuron residues affected barley and oats more severely than did diuron residues. Accumulation of diuron and monuron from annual applications at rates used for selective weed control in cotton appears unlikely.

The control of blue oak (Quercus douglasii H. & A.) was investigated by cut surface applications of water-soluble amine formulations of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP), 2-(2,4-5-trichlorophenoxy)propionic acid (silvex); ester formulations of 2,4,5-T and silvex; potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram); and ammonium sulfamate. All phenoxy herbicides were relatively effective in controlling blue oak; the least favorable results were obtained with undiluted ester forms of 2,4,5-T and silvex, and ammonium sulfamate. Picloram was more effective than the water-soluble amine salts of 2,4-D on both blue oak and madrone (Arbutus mensiesii Pursh). Relatively favorable results were obtained on madrone by single-point applications to stems with picloram. Applications to holes 1 inch deep were more effective than when applied in deeper or shallower holes. Diluting alkanolamine salts of 2,4-D with water and butoxyethanol ester of 2,4,5-T with diesel oil had a generally depressing effect on kill (except for the first dilution of the ester). Plant kill decreased as the diameters of the trees increased. Rainwater analyses did not furnish an explanation for the marked increase in growth of the grass beneath the treated trees.

C14 ring-labeled atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) was applied in nutrient solutions. Soybeans absorbed more atrazine per g of fresh weight than corn or cotton. The amount of atrazine absorbed by the plants increased with increases in atrazine concentration, in water absorption, and in length of absorption. Less atrazine was absorbed in the second than in the first 24-period wtih occasional indications of loss of atrazine back into the solution. C14O2 evolution was not established for any plant although many different environmental conditions were tried. Degradation to C14O2 is not a significant process for these plants under these conditions.

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.

Giant foxtail (Setaria faberii Herrm.) germinated, emerged, and produced panicles containing viable seeds when sown during the greater part of the growing season. The height of the plant, size of panicle, and number of seeds produced depended on date of planting. Cutting to 2 inches at various stages of growth did not prevent further growth and reflowering but reduced the size of the panicle and the number of seeds. Mowing in May and June allowed giant foxtail to produce two crops of viable seeds.

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.

Three thiocarbamate herbicides, S-ethyl dipropylthiocarbamate, S-propyl dipropylthiocarbamate, and S-propyl butylethylthiocarbamate, applied at a depth of 1.5 inches in Tifton loamy sand were much more toxic to yellow nutsedge (Cyperus esculentus L.), sicklepod (Cassia tora L.), and Texas millet (Panicum texanum Buckl.) than when applied at 0.75 inches. The optimum depth of application may vary with different soils. Optimum subsurface placement was more effective than either soil incorporation or preemergence surface application.

Methionine-methyl-C14 administered to seedling tissue produces radioactive polymers consisting primarily of protein. Formation of polymer was inhibited within half an hour in susceptible species by 1, 10, and 50 ppm concentrations of isopropyl N-phenylcarbamate (IPC), isopropyl N-(3-chlorophenyl)carbamate (CIPC), methyl N-(3,4-dichlorophenyl)carbamate (swep), and 4-chloro-2-butynyl N-(3-chlorophenyl)carbamate (barban). Resistance to inhibition varied with plant species, and was in accord with previously observed responses in field work. Inhibition of amino acid utilization may be a fundamental cause of carbamate phytotoxicity. Formation of material tentatively described as lignin is also inhibited.

Mature yellow foxtail [Setaria glauca (L.) Beauv.] infestations, growing in rows of corn, were harvested in 3 foot segments from paired 30 foot rows of corn. Basic analyses of variance were calculated so that the variances of plot sizes involving multiples of 3 feet could be determined and compared. Precision indices were calculated for harvesting various fractions of the plot area. Loss of precision did not exceed 25 percent when only 40 percent of the total area was harvested in random samples of 1-row X 3 feet, or in multiples of this basic unit. Practical implications of the findings are related to estimates of weed yields in crop-weed ecology studies and herbicide evaluation tests.