Soil samples with and without a past history of dimethyl-2,3,5,6-tetrachloroterephthalate (DCPA) treatment were obtained from New York. A third sample was obtained from a field in Colorado where DCPA had been ineffective as a herbicide. The populations of bacteria and actinomycetes in these soils were determined and the actinomycetes were more prevalent in the samples with previous DCPA treatment than in untreated samples. Subsequent treatment resulted in an increase in actinomycete population and little change in bacterial population. In pure culture and in soils, the addition of DCPA had no adverse effect upon microbial growth, and several microorganisms appeared to utilize the herbicide as a carbon source. Two degradation products were methyl-2,3,5,6-tetrachloroterephthalate and 2,3,5,6-tetrachloroterethalic acid.

Foliar treatments of 4-amino-3,5,6-trichloropicolinic acid (picloram) induced rapid procambium activity in western iron-weed (Vernonia baldwini Torr.) leaves. Increased meristematic activity was followed by destruction of the phloem parenchyma, sieve elements, and companion cells. Cell destruction in the vascular bundle was concomitant with that in the mesophyll.

The effect of 1,4-naphthoquinone, 1,4-benzoquinone, and several CI and NH2-substituted quinones has been studied on growth, chlorophyll concentration, and oxygen evolution in Chlorella pyrenoidosa Chick. (Emerson strain). Drastic decrease of the studied parameters usually was noted after 24 to 48 hr treatment at 3×10–5 M concentration. The effect of the quinones was compared with that of 6,7-dihydrodipyrido [l,2-a:2,l-c-]pyrazidinium salt (diquat) and 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron). Diuron inhibited oxygen evolution immediately after addition, but could be washed out and the effect was reversible. Diquat had no inhibitory effect on oxygen evolution and chlorophyll content but caused a slight decrease in cell number. Although some quinones have an almost immediate effect on the oxygen-evolving mechanism, it seems more likely that the overall effect of the quinones is on the total physiological activity of the algal cells. Oxygen evolution seems to affected earlier than chlorophyll destruction, and the observed long-term damage is irreversible. Most of the compounds studied could be classified as algicidal, with the exception of diuron, diquat, and 1,4-benzoquinone which may be considered to be algistatic.

Thirty herbicides were tested for possible effects upon the incorporation of radioactivity from malonic acid-2-14C into lipid by excised hypocotyls of hemp sesbania (Sesbania exaltata (Raf.) Cory). Concentrations of 1 to 20 mg/L were used. Inhibition was caused by 3-nitro-2,5-dichlorobenzoic acid (dinoben), 2-chloro-N,N-diallylacetamide (CDAA), 2-chloroallyl diethyldithiocarbamate (CDEC), 7-oxabicyclo(2.2.1)heptane-2,3-dicarboxylic acid (endothall), 2,6-dichlorobenzonitrile (dichlobenil), 3,5-diiodo-4-hydroxybenzonitrile (ioxynil), and pentachlorophenol (PCP). At 1 mg/L, stimulation was caused by 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 3-amino-2,5-dichlorobenzoic acid (amiben).

Combinations of 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron) with O,O-diethyl S-2-(ethylthio)-ethyl phosphorodithioate (disulfoton) or O,O-diethyl S-(ethylthiomethyl) phosphorodithioate (phorate) in soil resulted in synergistic phytotoxicities. These synergistic phytotoxicities persisted 21 to 27 weeks in alternately fallow-cropped soils treated with 0 to 12 ppm disulfoton or phorate and 0 to 1.0 ppm diuron where oats (Avena sativa L., var. Mark-ton) was the bioassay plant, and persisted 5 to 15 weeks in alternately fallow-cropped soils treated with 0 to 12 ppm disulfoton or phorate and 0 to 1.33 ppm diuron where corn (Zea mays L., var. US 13) was the bioassay plant. The persistence of the combined pesticides corresponded closely with persistence of the individual pesticides. Corn and cotton (Gossypium hirsutum L., var. Acala 4-42) were more tolerant than was oats to diuron and diuron-insecticide combinations.

Spring parsley [Cymopterus watsonii (Coult. & Rose) Jones] was examined for phototoxicity by chick (Gallus domesticus, Arbor Acre 50 x Vantress hybrid) bioassay, after treatment with 2,4,-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 4-amino-3,5,6-trichloropicolinic acid (picloram), and an approximate 4 to 1 mixture of 2,4-D and picloram. Spring parsley leaves treated with picloram and picloram-2,4-D were much less phototoxic to chicks than controls 4 weeks after treatment. When treatment was followed by warm weather, leaves treated with 2,4-D and 2,4,5-T were not phototoxic 4 weeks after treatment at the highest single dose that could be administered.

Absorption, translocation, and metabolism of 14C-labeled 2,4-bis (isopropylamino)-6-methylmercapto-s-triazine (prometryne) from solution cultures by cotton (Gossypium hirsutum L., var. DPL smoothleaf) and soybean (Glycine max Merr., var. Lee) were investigated. Cotton (moderately tolerant) and soybean (sensitive) absorbed essentially equal amounts of prometryne. Whereas 14C was uniformly distributed in soybean, it was concentrated in the lysigenous glands and in the root primordia of cotton. Soybean had a considerably higher concentration of radioactivity in shoots than in roots, whereas the reverse was true in cotton. The major methanol extractable 14C-labeled component in the roots and shoots of both species was prometryne. Both species converted some prometryne to the derivative, 2,4-bis(isopropylamino)-6-hydroxy-s-triazine (hereinafter referred to as hydroxypropazine), but cotton shoots had a slightly higher percentage of the latter than the soybean shoots. The concentration of prometryne in soybean shoots was about four times greater than in cotton shoots. Differential translocation of prometryne appeared to be a major factor contributing to the difference in susceptibility between cotton and soybean.

Inhibition of cotton (Gossypium hirsutum L.) and soybean (Glycine max (L.) Merr.) lateral roots by alpha, alpha, alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) was directly related to depth and method of incorporation. Root inhibition of the crop plants was reduced when trifluralin was incorporated shallowly after planting with either a power tiller or a ground-driven tiller, to a depth no greater than 0.5 in above seed placement. A bioassay of the soil showed that disking trifluralin-treated plots before bedding caused the greatest retention of the material 3 weeks later, and that retention was less when the herbicide was applied and shallowly incorporated after planting. Further studies on the relationship of soil persistence of trifluralin to depth of incorporation 6 months after application, showed no herbicide present in plots not incorporated while only minimal residues were found where incorporation was no deeper than 1 in. Residues in plots incorporated below the 2-in depth were moderate at 0.5 to 1 lb/A rates and high at the 2 lb/A rate and above.

Fall treatments with 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) as opposed to cultivation during the growing season reduced hand labor requirements more than 70% for weed control in Japanese holly (Ilex crenata Thumb. Rotundifolia Hort.). The response of Japanese holly to simazine varied from superior growth and quality to severe injury and death. Simazine plus 3-amino-1,2,4-triazole (amitrole) resulted in better control of small weeds than simazine alone in late winter or early spring. Dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA), N,N-dimethyl-2,2-diphenylacetamide (diphenamid), and 2,6-dichlobenzonitrile (dichlobenil) reduced labor requirements for control of annual weeds without any visual response on the Japanese holly. In certain instances, rotations of herbicides were effective for broad spectrum weed control.

An experiment was conducted comparing wheat (Triticum aestivum L., var. Pembina) and wild buckwheat (Polygonum convolvulus L.) grown alone in pots, in full competition, and in root competition at three levels each of soil fertility and soil moisture, and harvested at three dates.

Wheat was a better competitor than wild buckwheat when considering dry matter production. With each succeeding harvest, the dry matter production and the total nitrogen and phosphorus uptake increased more for plants grown alone than in competition. Competition caused a reduction in the nitrogen and phosphorus content of wheat and wild buckwheat at the first harvest, while reductions in dry matter did not occur until the second harvest. Wheat increased in dry matter and nitrogen more than wild buckwheat with each higher level of soil moisture when grown alone but not when in competition. When grown alone or in competition, wheat increased linearly in dry matter production with increases in fertility while wild buckwheat produced maximum dry matter with medium fertility. The total nitrogen increased in wheat and wild buckwheat with each higher level of fertility, while total phosphorus increased only in wheat.

Wild buckwheat used less water than wheat to produce a gram of dry matter and per milligram of phosphorus uptake when grown alone, while the plants in competition were intermediate in water usage to plants grown alone. Wild buckwheat and wheat used similar amounts of water per unit of nitrogen uptake when grown alone and increased their water usage when grown in competition. Water efficiency for nitrogen and phosphorus uptake and dry matter production usually decreased with plant maturity and higher soil moisture, and increased with higher soil fertility.

Labeled 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2, 4, 5-T), 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 4-amino-3, 5, 6-trichloropicolinic acid (picloram), 1,2-dihydropyridazine-3,6-dione (MH), assimilates, and phosphoric acid were absorbed and transported basipetally from the lamina into the petioles of detached bean leaves (Phaseolus vulgaris L.). Upward transport in the lamina was slight, except when the petioles were in water. In contrast, labeled 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) was not transported basipetally, but some acropetal transport did occur. Vein-loading and transport of labeled assimilates, 2,4-D, dicamba, MH, and phosphate were greatly reduced by a prior treatment with 7-oxabicyclo(2.2.1)heptane-2,3-dicarboxylic acid (endothall). Detached leaves hold promise for use in absorption and transport studies.

The depths of leaching of S-ethyl dipropylthiocarbamate (EPTC), S-propyl butylethylthiocarbamate (pebulate), S-propyl dipropylthiocarbamate (vernolate), S-ethyl hexahydro-lH-azepine-l-carbothioate (molinate), and S-ethyl cyclohexylethylthiocarbamate (hereinafter referred to as R-2063) were compared in five different types of soils contained in glass columns. The depths of leaching in mineral soils were directly correlated with the water solubilities of the herbicides. The order of leaching from greatest to the least was molinate, EPTC, vernolate, pebulate, and R-2063. With all compounds tested, the depth of leaching decreased as the clay content of the soil increased. Leaching depth also decreased as organic matter increased. In peat soil containing 35% organic matter, no movement out of the treated zone could be detected with any of the thiocarbamate herbicides tested when leached with 8 in of water.

n-Pentane was used to extract 3-(m-trifluoromethylphenyl)-1,1-dimethylurea (fluometuron) from soil-water samples. The microgram quantity of fluometuron in the n-pentane was measured at a wavelength of 242 mμ with an ultraviolet spectrophotometer and this measurement related to the fluometuron concentration in the soil-water sample. No measurable interference was noted in the n-pentane after the extraction of fluometuron from the soil-water samples. The procedure was developed for extracting and quantitatively determining fluometuron in soil-water samples.

Quackgrass (Agropyron repens (L.) Beauv.) was defoliated for 25 to 30 days with applications of 1.0 lb/A of l,l′-dimethyl-4–4′-bipyridinium salt (paraquat). Applications were more effective made prior to darkness than at midday. Phytotoxicity was increased by adding surfactants in the field, and experiments utilizing 14C-paraquat under controlled environmental conditions indicated that the surfactant X-77 increased foliar absorption by 20%. Quackgrass plants grown in nutrient solutions exhibited chronic paraquat toxicity which increased as the nitrogen levels increased. Paraquat also inhibited the growth of lateral buds on quackgrass rhizome segments cultured in the dark. Greater movement of 14C-paraquat in quackgrass leaves occurred under 6 hr of light as compared to 6 hr of darkness following application. However, a 6-hr dark period after application prior to the light period further enhanced the movement from the treated leaf.

Simultaneous treatment with certain carbamate insecticides inhibited degradation of 3-(p-chlorophenyl)-1,1-dimethyrurea (monuron) in cotton (Gossypium hirsutum L.) leaf discs. Monuron degradation was strongly inhibited by 1-naphthyl methylcarbamate (carbaryl) and 4-benzothiophene-N-methylcarbamate, but 2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate was ineffective. Effective carbamates did not prevent the metabolism of monuron to 1-(p-chlorophenyl)-3-methylurea (hereinafter referred to as monomethylmonuron), but they inhibited subsequent degradation of monomethylmonuron.

In 1965–66, we observed root development of two plant types of rush skeletonweed (Chondrilla juncea L.). Rosette bud formation on both plant types occurred on the upper 5-cm zone of the taproot after seed dispersal in the fall until flower-stem initiation the following spring. Incubation at various temperatures of lateral root sections from field grown plants showed a cyclic sprouting pattern with the highest percentage during late fall and early spring, and no sprouting during June. Bud production was most frequent at the proximal end of the sections. The earlier-flowering plant type contained an average of 6.7 and 6.0 major roots after 6 and 18 months of growth whereas the late-flowering type contained 10.7 and 16.0 major roots for the same periods of growth. The early-flowering plant roots were larger in diameter than those of the late-flowering plants. Both root types increased in diameter as distance from the point of attachment increased excluding root apex. Unattached secondary plants resulting from vegetative propagation were found of both plant types.

Under field conditions in North Carolina, yearly retreatment was required to provide reasonable soil sterility when an initial rate of 40 lb/A was used for each of the compounds 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). Lateral movement of these three herbicides was a major factor limiting their utility as soil sterilizers. Attempts to reduce lateral movement by using reduced herbicidal rates in combination with contact active additives were partially successful. The total soil sterilization performance index derived from sterility ratings and lateral movement ratings indicated that the combination of 5 lb/A of diuron and 2 lb/A of 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat) could not be excelled by diuron or 5-bromo-3-isopropyl-6-methyluracil (isocil) regardless of the rate used. When used alone, the soil sterilization properties of diuron were equivalent to those for isocil, provided that the diuron rates were two and one-half times as great as those for isocil.

Three experiments were conducted in the greenhouse to study the effect of 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat) when sprayed directly on seeds at the soil surface. Germination of alfalfa (Medicago sativa L., var. DuPuit) and red clover (Trifolium pratense L., var. Kenland) was not affected at 1 1b/A paraquat, but germination of Kentucky bluegrass (Poa pratensis L., var. Newport) and perennial ryegrass (Lolium perenne L., var. Linn) was severely reduced at that rate. A protecting layer of soil approximately 0.25 inch thick was completely effective in protecting the seeds from the effect of paraquat. Germination of seven other grass species was reduced by 0.5 1b/A paraquat.

Oxygen uptake and oxidative phosphorylation were inhibited by 10–4 M of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) in isolated mitochondria of corn (Zea mays L., var. Dixie 18), Sorghum (Sorghum vulgare Pers., var. Early Hegari) and Soybean (Glycine max L., var. Lee). Little or no inhibition was detectable at 10–5 and 10–6 M in corn and sorghum. Data for 4-(methylsulfonyl)2,6-dinitro-N,N-dipropylaniline (nitralin) were more variable but similar. The effects on these processes do not seem to be related to the selectivity of trifluralin since it caused a greater reduction in oxygen and phosphate uptake in resistant species (soybean) than the susceptible species (sorghum).