Optimum temperature for bud activity and shoot growth of quackgrass (Agropyron repens (L.) Beauv.) occurred between 20 and 27 C. CO2 and O2 gas concentrations normally occurring in soil air were not found to affect bud activity and shoot growth appreciably.

In agar cultures 1-naphthaleneacetic acid (NAA) reduced bud activity of quackgrass (Agropyron repens (L.) Beauv.) rhizomes, while indole-3-acetic acid (IAA) had little effect. Gibberellic acid (GA) acted antagonistically with NAA. Maleic hydrazide (MH) had less effect on bud activity than isopropyl N-phenylcarbamate (IPC), 2,3,6-trichlorophenylacetic acid (fenac), or phenoxy compounds at high rates. GA or its active metabolite was translocated throughout the plant. 2,3,5-Triiodobenzoic acid stimulated bud activity on intact rhizomes.

Polychlorobenzoic acids (PBA), 2,3,6-trichlorobenzoic acid (2,3,6-TBA), and 2,3,6-trichlorophenylacetic acid (fenac) sprays were applied safely for the eradication of perennial weeds at not over 20 pounds per square inch in winds less than 11 miles per hour in and near cotton. Use of these herbicides near soybeans was hazardous because very small quantities of them caused leaf deformities and some loss in seed yield.

Herbicidal control of tall larkspur, Delphinium occidentale Wats. was investigated in the Sawtooth National Forest near Oakley, Idaho. When larkspur was in a prebud stage, 4 and 8 lb/A of the propylene glycol butyl ether esters of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) gave good control, with significant increases in yield of native grasses. At the bud and flower stages neither herbicide gave satisfactory control at 12 lb/A. Granular silvex at 400 lb/A total product (80 lb/A ae) killed all larkspur with only slight injury to rabbitbrush, sagebrush, and native grasses. A chlorate-borate (25%–75%) mixture gave a complete larkspur kill at 1740 lb/A.

Smooth bromegrass, Bromus inermis, and red fescue, Festuca rubra, were sown in 1952 on a fertile soil severely infested with yellow toadflax, Linaria vulgaris Mill., in the Peace River section of Alberta. Annual applications of 2,4-dichlorophenoxyacetic acid (2,4-D) were made at late flower-bud stage at nil, 1, 2, 3, and 4 lb/A acid equiv. In 1958, the average per cent of toadflax in the brome was 1, 0.5, 0.5, 0, and 0, respectively. Red fescue had 6 to 0.1% of toadflax. All rates of 2,4-D prevented seed production. The sods were broken in 1959, and toadflax re-established strongly on all plots from dormant seed and residual plants. In 1961, the brome, rejuvenated by breaking, strongly suppressed toadflax, while fescue failed to compete with it.

Twenty-nine s-triazines were evaluated as subsurface and surface preemergence sprays for the control of crabgrass in corn, grain sorghum, soybean, and cotton and as directed postemergence sprays in cotton. In preemergence experiments corn was tolerant to most chloro-alkylamino-s-triazines but was severely injured by most methoxy- and methylmercapto-alkylamino-s-triazines. 2-Chloro-4,6-bis(isopropylamino)-s-triazine [propazine], 2,4-bis(ethylamino)-6-trichloromethyl-5-triazine, and 2-chloro-4-isopropylamino-6-methylamino-s-triazine were about equally effective for selective preemeregnce weed control in grain sorghum. 2,4-Bis(ethylamino)-6-trichloromethyl-s-triazine and perhaps 2-methoxy-4,6-bis [(3-methoxy)propylamino]-s-triazine were sufficiently active and selective to suggest additional evaluation as preemergence herbicides for soybeans. Cotton exhibited tolerance to certain methylmercapto derivatives; 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine [prometryne] as a preemergence and as a directed postemergence spray appeared especially promising for control of weeds in cotton. Generally methoxy- and methyl-mercapto-alkylamino-s-triazines as preemergence and postemergence sprays were more effective for controlling crabgrass than corresponding chloro-alkylamino-s-triazines. The initial and residual toxicities of 14 of the more promising s-triazines were compared in four soils of the southern United States. Initial effective levels of the methoxy and methylmercapto derivatives varied more among soils than those of corresponding chloro derivatives. In most cases methoxy s-triazines were more toxic to the fifth oat crop than corresponding chloro s-triazines whereas chloro s-triazines exhibited the greatest initial toxicities. Certain methylmercapto derivatives appeared fairly persistent also.

Techniques were developed for evaluating herbicides on submersed, floating, and emersed aquatic weeds. Among 75 herbicides evaluated on three species of submersed weeds only 1:1′-ethylene-2:2′-dipyridylium (diquat); 1:1′-dimethyl-4:4′-dipyridylium (paraquat); di-N,N-dimethylcocoamine salt of 3,6-endoxohexahydrophthalic acid (endothal); and acrylaldehyde (acrolein) gave 85 percent or better control at 1 ppmw in still-water tests. Only acrolein and the di-N,N-dimethylcocoamine salt of endothal were effective on submersed weeds at 1 ppmw in the limited-exposure test. The evaluation of 17 herbicides on three species of floating aquatic weeds indicated that diquat was effective when applied at rates of 1 or 2 lb/A. The tertiary fatty acid amines of 2,4-dichlorophenoxyacetic acid (2,4-D) were more effective on floating weeds than an ester of 2,4-D. Many of the 78 herbicides evaluated on alligator-weed (Alternanthera philoxeroides (Mart.) Griseb.) killed the tops, but only two retarded the sprouting of underwater nodes longer than 6 weeks. Applications of 20 lb/A of 2-(2,4,5-trichlorophenoxy)-propionic acid (silvex) in two formulations retarded sprouting of underwater nodes for 8 weeks.

Treatment of woollyleaf franseria, Franseria tomentosa Gray, with 2,4-dichlorophenoxyacetic acid (2,4-D) at three locations in Nebraska showed that June treatments were much more effective in reducing the stand than those made in July and August. The isopropyl ester and butoxyethanol ester of 2,4-D were somewhat more effective than the triethanolamine salt. Rates of 2 and 4 lb/A gave the most consistent results.

The toxic effects of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) to barley were avoided by feeding plants treated with 1.5 lb/A of simazine, sucrose, glucose, aspartate, and maltose. Shoots from plants fed glucose and maltose contained more soluble carbohydrate than the check. Plants fed glutamine and asparagine were higher in total nitrogen content than the check. Plants fed sucrose and maltose increased their nitrogen content over the check, but plants fed glucose did not. The harmful effects of simazine occurred primarily in barley shoots exposed to light. Plants grown in the dark showed a very small decrease in weight of shoots and soluble carbohydrate content as the level of simazine increased, while the weight of the shoots and soluble carbohydrate content of treated plants grown in the light decreased sharply. Simazine had little effect on root growth of plants grown in the light or dark. The data on root respiration showed that barley roots metabolized the added substances differently and that simazine differentially influenced their metabolism by the roots.

Dalapon (2,2-dichloropropionic acid) was applied as basally directed sprays to field grown cotton (Gossypium hirsutum L. var. Acala 4–42). Herbicidal rates of dalapon applied after heavy boll development (approximately 105 days after planting) were noninjurious; earlier applications appeared hazardous. Three or six pounds of dalapon per acre applied during early square or full flowering caused no noticeable injury symptoms but delayed maturity and reduced cotton yields in proportion to dosage. Analysis of eight seed and fiber properties showed no significant differences among treatments except for minor shifts attributable to dalapon-induced changes in maturity. Germination of seed from treated cotton was measurably retarded but final viability was not reduced. The retarding influence persisted for more than two years in storage. Accumulation of 8 to 21 ppm dalapon in the seeds was demonstrated by colorimetric and isotope dilution methods of analysis.

The interaction of soil applied phosphorus and soil applied herbicides was investigated in field, greenhouse and controlled environment chamber studies. A previously reported diuron-phosphorus interaction could not be repeated under all conditions studied. Amitrole was consistently more toxic to plants grown under high phosphorus levels than under low phosphorus conditions. The phytotoxicity of ten other herbicides was not influenced by the phosphorus content of the soil.

Measurements of C14-labeled 2,4,5-trichlorophenoxyacetic acid absorbed and translocated from treated leaves of blackjack oak (Quercus marilandica Muenchh.) showed that absorption and translocation were highest in early spring and decreased during May and June, so that there was a minimum at about the first of July. Absorption and translocation increased during July, August, and September. Measurements of soil moisture did not reveal a correlation of water stress and translocation rates. Extensive variations in the respiration rates of the leaf tissue occurred during the growing season. The trends in respiration rates generally paralled the trends in translocation rates.

Field studies at three locations across Nebraska showed that 2,3,6-trichlorobenzoic acid (2,3,6-TBA) leached readily into the soil profile. The herbicide was lost from the surface soil much more readily in central and western Nebraska than in eastern Nebraska even though rainfall was about twice as much at the last location. Volatilization was suggested as a possible reason for this loss of 2,3,6-TBA. There was a definite, but not complete, loss of 2,3,6-TBA from the three soil profiles between May 1960 and September 1961. Soybeans proved to be an acceptable bioassay plant for this herbicide in soil at 2,3,6-TBA concentrations of ½ to 2 ppmw.

Rough pigweed (Amaranthus retroflexus L.) on the average emerged 2 days earlier than yellow foxtail (Setaria glauca (L.) Beauv.) The heading and maturity of both weeds seeded in corn was delayed for 3–4 days. The interval between emergence and maturity decreased progressively as seeding dates were delayed. The tallest plants and the highest yields were produced from the early spring seedings. Competition from corn depressed yields of both weeds more than their heights. Height and yield of foxtail seeded during July were most affected. In later seedings foxtail tolerated corn competition much better than pigweed.

The toxicity to bluegill sunfish (Lepomis macrochirus, Rafinesque) of 3 to 21 commercial 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-(2,4-DP)], and 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) was determined. The variations among formulations of the same herbicide were much greater than those among different herbicides. Variations in toxicity of a single formulation were also noted. Formulations of each herbicide were reported as either safe or unsafe for aquatic applications. Amine salts were generally less toxic to fish than esters. The formulation selected for use should be assayed prior to field application, using the receiving water.

Herbicide experiments conducted on flowering size gladiolus corms over a four year period have shown that 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at 1 lb/A pre-emergence and 1 lb/A at lay-by; ethyl N,N-di-n-propylthiolcarbamate (EPTC), 6 lb/A preemergence and 6 lb/A at lay-by; or 3(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) either 1 lb/A preemergence and 1 lb/A at lay-by or 2 lb/A at lay-by appear to be safe and effective herbicides for weed control on varieties Spic & Span, Valeria, Hopman's Glory, Spotlight, Elizabeth the Queen, Friendship, and White Excelsior.

The effect of mono-and dichlorophenyl analogs of N-phenyl-2-methylpentanamide (PMP) and N-(3,4-dichlorophenyl)-alkylamides on the photolytic activity (Hill reaction) of chloroplasts isolated from turnip greens (Brassica spp.) was studied. Photochemical activity was measured potentiometrically with ferricyanide as the electron acceptor. PMP inhibited the Hill reaction by 50 percent (I50) at 4.5 × 10-5 M. Monochlorination in the meta and para ring positions enhanced the inhibitory activity whereas chlorination in the ortho position negated inhibitory activity of the parent chemical (PMP). N-(3,4-dichlorophenyl)-2-methylpentanamide (3,4-DCPMP) was the most inhibitory of the 6 dichlorinated isomers (I50 = 5.8 × 10-7 M). Replacement of the imino hydrogen of 3,4-DCPMP with a methyl group reduced inhibitory activity below that of the unsubstituted parent compound (PMP). Of the straight-chain N-(3,4-dichlorophenyl)alkylamides studied, the propanamide expressed maximum inhibition. 2-Methylalkylamides were more inhibitory than the corresponding straight-chain alkylamides. Maximum inhibition in the branched series was obtained with 3,4-DCPMP. Kinetic studies performed with 3,4-DCPMP at different light intensities indicated that both light and dark reactions were inhibited. However, the light reaction was more sensitive to the effects of the chemical.

Most of the elongation responsible for barnyardgrass seedling emergence occurred in the first internode. The developing foliar leaves within the coleoptile were the consistent site of EPTC injury. Injury symptoms were never observed in the roots. The first internodes of EPTC-injured seedlings seemed to function normally, although they were sometimes kinked into zig-zag patterns. This kinking was a secondary rather than a direct effect of EPTC injury. Seed germination was not affected by EPTC. Injury occurred after germination. Exposing the seed and primary root to EPTC did not lead to injury, whereas exposing the shoot or only the coleoptile did. It was concluded that leaf tissue is the main site of EPTC uptake in barnyardgrass as well as the prime site of injury.

Foliar applications using volumes of 100 to 500 ml per acre were used to determine the effect of droplet size on herbicide toxicity to five plant species. Several types of plant response were used to indicate effectiveness. Herbicide toxicity increased as the particle diameter decreased from 0.3 mm to 0.1 mm.

Isopropyl N-(3-chlorophenyl)carbamate (CIPC), 2-chloroallyl diethyldithiocarbamate (CDEC), ethyl N,N-di-n-propylthiolcarbamate (EPTC), sodium 2,4-dichlorophenoxyethyl sulfate (sesone), and N-1-naphthylphthalamic acid (NPA) controlled Amaranthus palmeri S. Wats., (Palmer amaranth) Echinochloa colonum (L.) Link, (junglerice) and Sorghum vulgare Pers. var. sudanense Hitchc. (sudangrass) more efficiently when applications were followed by overhead irrigation, except in a few instances where weeds were controlled regardless of the irrigation method. More CIPC, sesone, CDEC, and EPTC penetrated below ¼ inch into soils, and they penetrated deeper with overhead irrigation.