The adsorption-desorption equilibria of chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea] in soil conformed to the Freundlich equation. Values of the constants, k and n, ranged from 4.2 to 12.3 and from 1.2 to 2.5, respectively, in eight soils. No significant linear correlation was detected between the Freundlich k values and soil texture, organic-matter content, pH, or water-holding capacity. Degradation studies were conducted using 14C-carbonyl-radiolabeled chlorbromuron in soil incubated at 18 or 32 C, with and without prior autoclaving, and with and without glucose enrichment. Degradation was enhanced by the higher temperature and glucose amendment, and it was retarded by autoclaving. Thin-layer chromatography indicated no accumulation of the monomethyl or monomethoxy derivative of chlorbromuron in any of the treatments. Chlorbromuron degraded rapidly in the incubation studies. Rapid loss of phytotoxicity was also noted in a greenhouse study with cucumber (cucumis sativus L. ‘Explorer’) bioassay. Phytotoxicity from 4 ppmw chlorbromuron had diminished to a very low level after 12 weeks.

Bromacil (5-bromo-3-sec-butyl-6-methyluracil) was much more effective in killing post oak (Quercus stellata Wangenh.) and blackjack oak (Q. marilandica Muenchh.) trees than 4-amino-3,5,6-trichloropicolinic acid (picloram) when applied to soil at 5.6 and 11.2 kg/ha in spots, bands, or by broadcasting. When applied at 5.6 kg/ha in bands or broadcast, picloram effected better crown reduction than bromacil on mockernut hickory (Carya tomentosa Nutt). Differences between rates and methods of applying bromacil were small. While bromacil was superior on the prevalent overstory species, post oak and blackjack oak, picloram excelled on the most numerous understory plants.

Two Louisiana sugarcane cultivars (interspecific hybrids of the genus Saccharum) CP 52–68 and L 60-25 were sprayed with herbicides commonly used for preemergence and postemergence control of johnsongrass (Sorghum halepense (L.) Pers.) and other weeds. The preemergence weed control treatments of 3-tert-butyl-5-chloro-6-methyluracil (terbacil) at 1.8 kg/ha and (2,3,6-trichlorophenyl)acetic acid (fenac) at 5 kg/ha were compared to a mixture of sodium salt of trichloroacetic acid (TCA) at 11 or 19 kg/ha plus 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) at 3.4 kg/ha (control). Herbicides were applied after planting in the fall, reapplied the following spring (after sugarcane emerged), and applied again in the second spring on the stubble crop (after sugarcane emerged). In the stubble crop the sodium salt of 2,2-dichloropropionic acid (dalapon) at 0, 5, or 10 kg/ha was applied as a postemergence spray over the top of sugarcane. In the factorial arrangement each cultivar received all combinations of the preemergence x postemergence treatments.

Terbacil did not injure either cultivar, but fenac injured both enough to reduce the yield of sugar in plant cane by about 10% as compared to the TCA plus silvex control. Stubble crop yields were not affected by fenac or terbacil. CP 52–68 was more tolerant to dalapon treatments than L 60–25. Both cultivars tolerated dalapon at 5 kg/ha relatively well although the yield of L 60–25 was reduced by about 5%. However at 10 kg/ha, dalapon reduced yields of CP 52–68 and L 60–25 by about 10 and 18%, respectively. Combinations of preemergence and postemergence treatments did not interact to reduce yields more than the combined effects of each treatment.

The degradation rates of 2,4-D [(2,4-dichlorophenoxy)acetic acid], dichlorprop [2-(2,4-dichlorophenoxy)propionic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], silvex [2,(2,4,5-trichlorophenoxy)propionic acid], dicamba (3,6-dichloro-o-anisic acid), and picloram (4-amino-3,5,6-trichloropicolinic acid) were determined in three soils. Herbicide breakdown was proportional to herbicide concentration, so half life of the various herbicides was calculated from linear regression of the logarithm transformed residue data. The average half life for 2,4-D, dichlorprop, silvex, 2,4,5-T, dicamba, and picloram were, respectively, 4 days, 10 days, 17 days, 20 days, 25 days, and greater than 100 days. The rate of degradation of 2,4-D was the same in all three soils, but for the other herbicides it was consistently faster in soil removed from under grass vegetation than from under trees.

Bromacil (5-bromo-3-sec-butyl-6-methyluracil) had no effect on germination but reduced growth of emerging shoots of orchardgrass (Dactylis glomerata L. ‘Virginia Common’) more than Kentucky bluegrass (Poa pratense L. ‘Merion’). Fresh weight gain and transpiration were reduced in orchardgrass seedlings at 0.125 ppmw of bromacil whereas 1.0 ppmw were required for reductions in bluegrass. Photosynthesis was inhibited in both plants; however, bluegrass recovered in 6 days. Water soluble carbohydrate content was greater and was not reduced as much by bromacil in bluegrass compared with orchardgrass. Absorption of 2-14C-bromacil from solution and translocation to shoots was directly related to transpiration rate. Bromacil was translocated acropetally from sheath and foliar treatments. Higher metabolic conversion of 2-14C-bromacil occurred in bluegrass compared to orchardgrass. Metabolites detected in plant extracts were 5-bromo-3-(2-hydroxy-1-methylpropyl)-6-methyluracil and an unknown. Traces of 3-sec-butyl-6-methyluracil and 5-bromo-3-sec-butyl-6-hydroxymethyluracil were also detected. Bluegrass tolerance involved high carbohydrate levels in tissues, hydroxylation of bromacil, and recovery of photosynthesis.

Seeds of five crop and 17 weed species were germinated with 0, 3, 6, and 10-bar water solutions of polyethylene glycol to simulate drought. With simulated drought, most weed species germinated better than soybeans (Glycine max L. ‘Hampton 266A’) but were not equal to pearlmillet [Pennisetum typhoides (Burm.) Stapf. and C. E. Hubb ‘Millex 23’] or sorghum-sudangrass [Sorghum bicolor (L.) Moench x S. sudanense (Piper) ‘SX-16’]. Prickly sida (Sida spinosa L,), sicklepod (Cassia obtusifolia L.), and Ipomoea lacunosa L. were the most tolerant weed species to simulated drought. Four species were intermediate in tolerance and four species germinated poorly under simulated drought. Hemp sesbania [Sesbania exaltata (Raf.) Cory] was the least tolerant and was similar to soybean.

Herbicides were evaluated for selectivity between three tall coarse grasses and three short fine grasses. Reed canarygrass (Phalaris arundinacea L.), quackgrass [Agropyron repens (L.) Beauv.], and smooth brome (Bromus inermis Leyss) were consistently more susceptible to amitrole-NH4CN (3-amino-s-triazole-ammonium thiocyanate) than three desirable short grasses, Kentucky bluegrass (Poa pratensis L.), creeping red fescue (Festuca rubra L.), and redtop (Agrostis alba L.). Reed canarygrass and redtop were more susceptible to dalapon (2,2-dichloropropionic acid) than creeping red fescue. Amitrole-NH4CN and dalapon combinations were more toxic to reed canarygrass, smooth brome, and redtop than creeping red fescue. Pyriclor (2,3,5-trichloro-4-pyridinol) was quite toxic to all grasses with Kentucky bluegrass showing the most tolerance. When TCA (trichloroacetic acid) was combined with amitrole-NH4CN results were similar to the dalapon combination but overall toxicity was reduced.

Nitrate reductase activity of seed leaves and the first three true leaves of tall morningglory [Ipomoea purpurea (L.) Roth] was shown to increase rapidly initially then gradually decrease. The greatest level of reductase activity of each true leaf was reached at the fourth to fifth day after unfolding. A subsequent leveling off of enzyme activity corresponded to the acceleration of leaf growth. Leaf nitrates were correlated with enzyme activity. The sum of leaf activities was used to estimate the total reductive capacity of the plant leaf tissue at each sampling date.

Seed were harvested from soybean [Glycine max (L.) Merr. ‘Cutler’] plants treated at flowering and pod filling with (2,4-dichlorophenoxy)acetic acid (2,4-D), 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB), and 3,6-dichloro-o-anisic acid (dicamba). Progeny of plants treated at flowering with 2,4-D and 2,4-DB or at pod filling with the lowest rate were normal. When higher rates were applied at pod filling, these phenoxy herbicides caused appreciable injury to the progeny in the form of reduced emergence and dry weight and malformed unifoliate leaves. Dicamba was much more injurious to the progeny of treated plants than 2,4-D and 2,4-DB. Even at low rates dicamba caused reduced germination, emergence, and dry weight and malformed first trifoliate leaves.

Chloroplasts, isolated from fresh spinach (Spinacia oleracea L.) were treated with four concentrations of each 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) or 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) to determine the influence of these herbicides on the free fatty acid content in isolated chloroplasts. The treated chloroplast solutions were sampled at 0, 5, 15, 30, 60, and 120 min following treatment. Results indicated that most herbicide treatments increased free fatty acid content in isolated chloroplasts when compared with the zero concentration treatments. The increased fatty acid content was similar for most concentrations of simazine and atrazine. Results of individual fatty acid analyses indicated that the increase in total fatty acids was a result of increases in concentration of unsaturated rather than saturated fatty acids.

Four field studies and two growth-chamber studies were used to evaluate the compatibility of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) in suspension fertilizer on corn (Zea mays L. ‘Pioneer 321’). Crop yields and tissue analyses were used to determine effects of atrazine on fertilizer availability. Visual and pictorial comparisons determined effects of fertilizer on atrazine phytotoxicity. Fertilizer-herbicide combinations compounded 230 days or sooner before application produced no change in atrazine phytotoxicity or fertilizer availability in growth chamber studies. Preplant-incorporated treatments displayed better fertilizer availability than preemergence treatments in the field. Preemergence treatments resulted in greater atrazine phytotoxicity under drought conditions. No problems of physical compatibility were encountered with the mixtures.

Isolated plant cells (Zinnia elegans Jacq. leaf tissue) and protoplasts (immature tomato fruit, Lycopersicon esculentum Mill.) were obtained by hydrolysis of pectic substances in the middle lamella and the primary cell wall, respectively. Both types of cells were stabilized in an inorganic salt solution and used to study absorption and distribution of four 14C-herbicides. Intracellular distribution within the protoplast was determined by ultracentrifugation in a discontinuous Ficoll gradient. Marked absorption of p-nitrophenyl-α,α,α-trifluoro-2-nitro-p-tolyl ether (fluorodifen) and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) by the isolated cells was observed; absorption increased with time. Trifluralin was retained within the cell more strongly than fluorodifen. Similar absorption patterns of fluorodifen and trifluralin by protoplasts were observed. Trifluralin was incorporated to a greater extent than fluorodifen by the cells and protoplasts. Trifluralin was distributed evenly between the mitochondrial and the chloroplasts-nuclei fractions; whereas fluorodifen was concentrated in the chloroplast-nuclei fraction. No significant absorption of 1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea fluometuron) or 3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea (chlorbromuron) was detected by either the isolated cells or protoplasts.

In pot culture experiments in the greenhouse, rice [Oryza sativa L. ‘Nova 66’], red rice [O. sativa L.], barnyardgrass [Echinochola crus-galli (L.) Beauv.], broadleaf signal-grass [Brachiaria platyphylla (Griseb.) Nash], northern jointvetch [Aeschynomene virginica (L.) B.S.P.], and hemp sesbania [Sesbania exaltata (Raf.) Cory] were seeded 1.3, 2.5, 5.1, and 10.2 cm deep in Crowley silt loam which was held at field capacity (24% moisture), saturation (34% moisture), or submerged 1.3 or 5.1 cm. At field capacity and saturation all species seeded 1.3, 2.5, and 5.1 cm deep emerged and grew well; seeding the plants 10.2 cm deep reduced emergence and growth. Submergence of the soil controlled all weeds effectively but reduced emergence and growth of dry-seeded rice.

The reduction in root yield (Y) of sugarbeets (Beta vulgaris L.) caused by specific densities (X) of kochia [Kochia scoparia (L.) Schrad.] was predicted by using the linear equation Y = 4.30 + 1.81 X. This equation was most accurate when the kochia density was 20 plants or less per 30.5 m of row. In 28 of 30 weed-control systems, where kochia densities ranged from 0.2 to 16.5 plants per 30.5 m of row, the predicted yield reductions were within 5% of the actual yield reductions.

Honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell], huisache [Acacia farnesiana (L.) Willd.], Macartney rose (Rosa bracteata Wendl.), live oak (Quercus virginiana Mill.), and whitebrush (Aloysia lycioides Cham.) were sprayed with herbicides alone and in mixtures. Mixtures of picloram (4-amino-3,5,6-trichloropicolinic acid) + dicamba (3,6-dichloro-o-anisic acid) at 0.56 + 0.56 and 1.12 + 1.12 kg/ha were most effective for killing honey mesquite in July. Picloram or picloram + dicamba were more effective for defoliating huisache than 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], dicamba, or other mixtures of herbicides. On Macartney rose picloram as the salt or ester was most effective, but some mixtures of picloram plus either 2,4-D [(2,4-dichlorophenoxy)acetic acid] or 2,4,5-T were as effective as picloram alone. On live oak, the most effective treatments generally contained at least 1.12 kg/ha of picloram either alone or in mixtures with dicamba or 2,4,5-T. Picloram alone killed as many or more whitebrush plants than MCPA [[(4-chloro-o-tolyl)oxy]acetic acid], dicamba, 2,4,5-T, 2,4-D, or mixtures.

Annual weeds were allowed to compete until or after each of the first three postemergence irrigations of furrow-irrigated cotton (Gossypium hirsutum L. ‘Deltapine 16’). Beds and furrows were shaped with a sectioned, rolling cultivator three times between cotton emergence and the second irrigation. Cotton boll components and fiber properties were not affected by periods of competition with annual weeds. Weeds allowed to compete after the first or second irrigations significantly reduced the 4-year average yield of cotton by 16 and 12%, respectively. Competition that began after the third or fourth irrigation, or that ended after the first, second, or third irrigation was less detrimental and did not significantly affect yields.

A 2-year experiment was conducted to determine the time interval between flowering and viable seed production in common milkweed (Asclepias syriaca L.). A high percentage of seeds harvested 6 weeks after flowering germinated. Seeds harvested 6 and 7 weeks after flowering resulted in seedlings with significantly shorter radicles and hypocotyls than seeds harvested 8 weeks after flowering. There was a close association between seed weight and radicle and hypocotyl length. Common milkweed produced viable seeds 5 to 6 weeks after flowering.

Seven herbicides were evaluated for the control of yellow nutsedge (Cyperus esculentus L.) in cotton (Gossypium hirsutum L. ‘Acala SJ-1’) in three field experiments during 1970 and 1971. The herbicides, 2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide (alachlor); 2-chloro-2′,6′-diethyl-N-(butoxymethyl) acetanilide (CP-53619); 2,4-bis(isopropylamino)-6-methylthio)-s-triazine (prometryne); 2-(α-naphthoxy)-N, N-diethylpropionamide (R-7465); S-isopropyl 5-ethyl-2-methylpiperidine-1-carbothioate (R-12001); 4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3-(2H)-pyridazinone (San-6706); and 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (methazole), were applied broadcast and incorporated 10 cm deep into the soil before the preplanting irrigation. All herbicides controlled nutsedge for at least 1 month in two or more experiments. Cotton was most tolerant to applications of 2.24 and 4.48 kg/ha of CP-53619, 3.36 and 6.72 kg/ha of prometryne, 1.12 kg/ha of San-6706, and 2.24 kg/ha of methazole. Higher rates of San-6706 and methazole and all rates of alachlor, R-7465, and R-12001 reduced the yield of cotton in one or more experiments.

Tomato (Lycopersicon esculentum Mill. ‘Campbell 17’) plant height and dry weight of tops decreased with increasing rates of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) and increased with increasing rates of phosphorus. Trifluralin and phosphorus interacted in their effects on root growth; phosphorus was less effective in promoting root growth as the rate of trifluralin increased. Phosphorus content of plant tops increased with each increment of soil-applied phosphorus at 0 and 0.84 kg/ha of trifluralin, but each increment of applied phosphorus did not significantly increase plant phosphorus content at higher rates of trifluralin. The inhibitory effect of trifluralin on phosphorus uptake diminished with time in 1969. Interactions between trifluralin and phosphorus did not occur in 1970.

The bacterially produced phytotoxin 2-amino-4-(2-amino-3-hydroxypropoxy)-trans-3-butenoic acid (rhizobitoxine) was tested for herbicidal properties in comparison with 3-amino-s-triazole (amitrole) and 4-chloro-5-(dimethylamino)-2-(a,a,a,-trifluro-m-tolyl)-3(2H)-pyridazinone (metflurazone). In postemergence tests with various plant seedlings, rhizobitoxine and amitrole were approximately equal in phytotoxicity on a weight basis, and both were generally much more phytotoxic than metflurazone. Phytotoxicity of rhizobitoxine varied markedly among grass species. Sorghum (Sorghum bicolor (L.) Moench ‘Hegari’) was very sensitive to rhizobitoxine, large crabgrass (Digitaria sanguinalis (L.) Scop.) was moderately sensitive, wheat (Triticum aestivum L. ‘Thorne’) was tolerant, and Kentucky bluegrass (Poa pratensis L.) was very tolerant. In contrast, amitrole was almost as phytotoxic to bluegrass as to large crabgrass, and metflurazone had little effect on either. In a preemergence test with mustard (Brassica japonica (L.) Coss. ‘Southern Giant Curled’) rhizobitoxine was as effective as amitrole, when compared on a molar basis, in inhibiting chlorophyll synthesis and root growth and was superior in retarding overall growth and development.